A mind-set that admits to things like logic and intuition; not necessarily those things by our definitions, but things like them.
At least some resemblance to living things with which we are familiar. They eat, sleep, reproduce, etc.; they are clearly organic beings, or else Mechanical Lifeforms.
Sometimes, however, they are too alien and their language, mind-set and culture remain incomprehensible to humans. Often (particularly if the beings can't communicate easily with humans) they will be presumed to be evil by the human protagonistswithout any actual proof. But in accordance with We Come in Peace — Shoot to Kill, starfish aliens who run across innocent, open-minded humans are themselves known to do beyond-horrible things to them, then excuse themselves later with an explanation that they were only trying to communicate with or greet us in the way they know how. Usually, their language and communication are so different from ours that if there is to be any communication between our species and theirs, it must be done by technological means of translation or them taking on a form humans can interact with.
Given the long, strange history of life on Earth (a given house includes such a bewildering variety of life as humans, houseplants, pets, spiders, molds, bacteria, etc.), it's likely if we ever actually encounter alien life, it might fit in this category. Species that evolve naturally would have adapted to solve similar basic problems: obtaining food/necessities, negotiating natural disaster, adapting to new circumstances, avoiding contamination by pathogens, competing with other species, competing with themselves, and so forth. So we would expect to find at least a few familiar aspects to their psychology as opposed to sheer indecipherable mystery... if they evolved in similar conditions as us.
When a story is told from the point of view of Starfish Aliens, and other decidedly non human creatures it's Xenofiction.
Aliens that don't look like humans, but still have basically the same body type are Humanoid Aliens, or Intelligent Gerbils, if they're obviously based off a particular Earth animal. Insectoid Aliens effectively split the difference.
These are much more common in animation, video games, and literature than they are in live-action media, due to the likelihood of Special Effects Failure. They are located towards the "hard" end of the Sci-Fi Hardness Scale.
Prone to enter Grotesque Gallery. May speak a Starfish Language.
See also Bizarre Alien Biology, Starfish Robots, and Our Monsters Are Weird. Compare Eldritch Abomination (both tropes have some overlap). For the first time mentioned in H.P. Lovecraft's At the Mountains of Madness, written in 1931. Here the author directly describes the Old Ones as "starfish aliens."
The Data Overmind in Haruhi Suzumiya is some kind of non-corporeal, out-of-phase "data-lifeform." note It's a concept based on an old theory that states that in its most basic form, the entire Universe is merely quantifiable information that can be manipulated; the Overmind is supposed to be a gestalt consciousness born of that information. What exactly it/they is/are, or how it/they think/thinks is never really explained, instead we get a lot of Techno Babble. Important to know is that its/their mind vastly differs from that of humans and that it/they does/do not communicate through language and therefore created the Interfaces (Yuki, Asakura, Kimidori) as its/their mediums. It appears that the entity/entities has/have different "voices" in itself with different opinions. The majority of them wishes to maintain the status quo and observe Haruhi safely. Oh, and they can hack reality. Playing up on their godlike nature, in one short story Kyon is contacted by an old school acquaintance who had fallen in love with Yuki at first sight and now worships the ground she stands on. It turns out that he had the minor power to see her connection to the IDE which consequently overloaded his brain, as no mere mortal could possibly comprehend its true form.
In the later light novels, another entity similar to the Data Overmind is introduced, the Sky Canopy Domain/Macrospatial Quantum Cosmic Existence. While having a similar non-corporeal, reality warping nature as the Data Overmind, its mindsets and motivations are so different they are alien even to the Overmind itself. They are so alien to each other that despite knowing of each other for millennia they are totally unable to communicate, and the little contact the two entities have had is through a coincidental meeting of Yuki and Kuyou Suou on Earth, the latter being the Domain's human interface, and one much worse at fitting in than any of the Overmind's.
And of course, the Quintessons from Generation One, and their Expy Alpha Q from Transformers Energon.
All of the Mushi in Mushishi are pretty much these.
The Angels of Neon Genesis Evangelion appear to be these, or at least the ones that don't cross into Eldritch Abomination territory. While Adam, Lilith and Sachiel are humanoids, the others have some bizarre appearances: Armisael is a double helix-shaped loop that forms into a tentacle; Ramiel is a regular octahedron who does some impossibly cool shapeshifting; Iruel and Bardiel are sentient nanoviruses etc.
Voices of a Distant Star - the Tarsians possess a starfish-like structure. In addition, miscommunications between them and humanity is implied to be one of the reasons why humans are fighting a war with them.
The ELS (Extraterrestrial Liquid-metal Shapeshifters) in Gundam 00: A Wakening of the Trailblazer. Their name alone should give you an indication of how bizarre they are. For one thing, they appear to live in gas giants, they are basically massive hunks of metal that can take on any shape they wish, they can assimilate other forms of life and technology into themselves, and they have no concept of communication beyond their own Hive Mind; when they encounter something unknown, their first instinct is assimilation to understand it. That includes everything from planets to complex machinery to human flesh.
The Gauna from Knights Of Sidonia are a sort of space fetus with a central body/core of some sort, with the ability to rapidly change and adapt. Humanity has been unable to communicate with them in any way beyond violence. The eponymous ship contains humanity's last remnant.
The aliens in Tsuritama are literally fish aliens. They have human and fish forms, require water to live and can communicate through it. Whenever they try it with humans though, it ends up as Mind Control.
The Green Lantern Corps has Bzzd (an insectoid), Medphyll (a plant being), Chaselon (an intelligent crystal), Cario and Dkrtzy RRR (an intelligent equation), Leezle Pon (a superintelligent smallpox virus). Mogo (a sentient planet), Rot Lop Fan (who, being from a sector of space where no light exists, is under the impression that he is a member of the F-Sharp Bell Corps), a race of hivemind spores, and the Black Mercy, a Hive Mind Planet/fungus thing that can alter gravity.
Legion of Super-Heroes has had a few members who fall into this trope. Tellus is the best example from the original continuity. Gates from the rebooted and current continuity. The Gil'dishpan race vaguely resemble psychic purple tubeworms with club-tails floating in water-filled orbs.
The Marvel Universe also includes the Brood, a blatant Alien ripoff ... er, nonhumanoid insectoid race that implant their young in unwilling humanoids.
There's also the Technarchy, a race of "techno-organic" creatures that think and speak more like machines than organic creatures, change shape and look like random masses of circuitry in their natural forms, and eat by infecting other creatures with a virus that makes them techno-organic also and then draining the life energy out of them. Their Hive Mind offshoot the Phalanx would also qualify.
Mojo of the X-Men books is the most visible representative of a race of pseudo-anthropomorphic slugs who use exoskeletons and motorized platforms to get around.
During Alan Moore's legendary run on Swamp Thing, the eponymous hero encountered a sentient biomechanical planetoid, which proceeded to rape him.
Matt Howarth did an entire series about ?sexual Life Partners Konny and Kzu, neither of whom looks remotely human-like — in fact, there are no humanoid aliens in the strip and books.
Also, the comic set as fiction in that 'verse, The Mighty Virus — a superheroic virus colony, complete with a cape hanging off of its flying environment globe.
Valerian has alien species ranging from simple Rubber-Forehead Aliens to things that definitely belong in this category. Giant, telepathic worm-things? Gelatinous shape-shifting prostitutes? Jellyfish-like mammalian math geniuses? And that's just the species that are categorized as people; the "animals" are even weirder. No wonder the creators have published a whole book dedicated just to their aliens.
Top 10's Vigilante from Venus is a giant worm/insect/jellyfish nightmare in her true form. No wonder she poses as a Green-Skinned Space Babe to make adult films — although some of her porn work involved her natural form. *Squick*
Aliens in The Far Side are usually depicted as semi-humanoid blobby creatures with numerous tentacles with eyes on the ends growing out of their bodies. They're almost invariably huge, capture humans like bugs (to which they are the size of), and speak random gibberish (unless understanding what they say is necessary for the joke).
Empowered has (at least) one race of them. They're huge (their liver weighs 700 kilograms alone!), have three eyes, and their veins seem to be on the outside of their bodies.
In Marvel Comics, the symbiote that makes up half of Venom is basically a black blob of slime. It's rarely depicted as so, however.
Planet Hulk introduced the spikes; a race at least superficially similar to the above-mentioned symbiotes; masses of slime. In their natural state, they're peaceful creatures that float through the vacuum of space feeding off cosmic radiation. When confined to a terrestrial environment, however, the atmosphere starves them to the point of madness, and they're forced to latch on to native life forms and infect them like parasites, causing spiked protrusions (hence their name) to jut out from the victim's flesh, essentially turning them into Parasite Zombies.
Eugenesis goes into some detail about the Quintesson (See Western Animation below), and their origins. Since they're neither fully organic or fully mechanical, they aren't born in the traditional sense, and tend to be born via budding. Mention is made of some of the original Quintessons being rolled like dough from Unicron's surface.
The two-part National Geographic Speculative DocumentaryExtraterrestrial (aka Alien Worlds) has fairly alien creatures. Species include gulp-hogs (wingless-bird-type hunters that evolved from squid-like creatures), mudpods (hexapodal stalk-eyed amphibians), skywhales (exactly what it says), kites (tentacled aerial predator shaped like its namesake), helibugs (almost-literal starfish aliens with three-point radial symmetry), stalkers (another triradial species, with an insect-like social structure and collective intelligence), etc.
Star Wars has the Hutts, specifically the famous Jabba the Hutt, a slug with a face and arms.
The aliens from 2001: A Space Odyssey are so alien that they can't even be shown on screen. The novels imply that they started as Starfish Aliens, but later transformed themselves into Mechanical Lifeforms, and eventually into Energy Beings. The author felt like showing the aliens would inevitably diminish their impact; in a supplementary book called Lost Worlds of 2001, the author records failed experiments with writing about both Human Aliens and worlds filled with Starfish Aliens, before he finally decided to have the monoliths be the last relics of an unseen, long ago vanished civilization.
The aliens in District 9 have two functional arms, two legs and a central head, but that's about where their resemblance to humans ends. They're all 'worker drones' who, without a queen, have little initiative of their own, with digitigrade limbs, an additional pair of tiny arms on their stomach, chitinous exoskeletons, antennae, claws, mandibles, tentacles, and all number of other insect- or crustacean-like attributes. The human residents of Johannesburg even call them "prawns". In a deleted scene, it is explained that the prawns have one gender and reproduce asexually. In that scene the humans claim that prawns have no attachment to their offspring, but this is shown to be a lie in the film, one of the many human attributes posessed by Christopher Johnson.
Astro Boy has one pop up for Astro to challenge just before the cut to credits, likely as a nod to his alien-fighting ways in the original.
The alien in question is the Artificial Sun (which was a man-made creation in the original anime,) and is basically a small (at least compared to the actual Sun) one-eyed sun with Combat Tentacles.
The Alien invader in Panico en el Transiberiano / Horror Express is an entity of thought or very mean Energy Being. It can take over people's minds—several at a time, be they dead or alive. Those it possesses have their minds cleaned out by removing the wrinkles in the brain so they can't think. The only telltale clue is that those possessed by it eyes glow red in dim light.
Red Planet sorta counts. Sure, the surprise aliens look very familiar (They closely resemble Earth cockroaches or crickets, but are considerably larger, quite more aggressive, are omnivores (eating one of the astronauts as well as most of the algae the humans had bombarded Mars with in an attempt to terraform the planet), photosynthesize, have chameleonic abilities and, to top it off. They live on Mars, en-masse!
The alien from the low-budget Invader was distinctly nonhumanoid, even being able to reconfigure its form - not by shapeshifting, but rather by unfolding, extending and withdrawing parts of its body.
The Thing (1982). There really is not a word other than "The Thing" to call it, because no one even really knows what it is. It is capable of perfectly replicating anything it has ever come in contact with, and every single cell of its body is a separate, hostile organism. It's so utterly alien that people aren't even sure if it has a true form or not, even the huge, grotesque monstrosity it forms in the end.
In The Thing (2011), the original version of the film, the "pilot version", shows the alien pilot of The Thing's ship. Words quite literally can't convey how weird it is, and since it committed suicide, it wasn't corrupted by the monstrosity, which first appears as a rather unimpressive giant bug.
The invaders in Battle: Los Angeles appear to be this. They look vaguely humanoid, but their bodies are some form of cybernetic and biological construct that is grown to specific battlefield needs, and their primary interest in Earth is its water supply and habitable conditions.
The xenomorphs from the Alien film series seemed surprisingly human for the first two films, considering their life cycle. In Alienł, however, we see what happens when one hatches from a dog...and it looks like a dog. The second Alien vs. Predator film features a xenomorph that hatched from a Predator. While it was still humanoid, it was significantly larger than the common human-hatched xenomorphs and had additional physical characteristics modeled after the Predators, such as a set of four mandibles around its mouth and head appendages that resembled a Predator's trademark dreadlocks. This implies that a xenomorph's physical characteristics are based on the species it hatched from and the common humanoid xenomorphs are only what they look like when they incubate in a human. We've never seen their native form. This would seem to raise questions about the humanoid-but-fifteen-foot-tall Queen, until you recall the Space Jockey from the first movie, which might explain why his ship was full of eggs when the species reproduces like ants. This was confirmed in Prometheus, which reveals the modern Xenomorph to be the result of a "goo"-infected human impregnating a woman, with the resulting creature then impregnating an Engineer. The chain of DNA is still ongoing; since the Xenomorphs evolved through artificial means, their genes are apparently still co-dominant with other lifeforms.
The alien in Dark Star, which looks like a beach ball with eyes and feet.
The titular creatures in the British sci-fi film Monsters(2010).
The creatures from The Abyss definitely qualify. They're classed as aliens by fans of the film even though they come from underwater instead of outer space (as far as we know). They're certainly strange in appearance and they are able to completely manipulate water - the Director's Cut reveals they caused the storm on the surface and created tidal waves ready to bury most of the world's cities - and in one case one alien creates a huge long strip of solid water and is able to morph it to resemble Lindsey's face.
The title character in Starman - we only see his true form at the very beginning, which looks like a giant glowing ball. He can only interact with other species by cloning a temporary body for himself (sort of an environmental suit). The cloning proceedure itself can be a bit unnerving, although the alien is quite friendly once you get to know him.
Forbidden Planet had the Krell - we never see them, there's no surviving record of their appearance, but their triangular door shapes and headsets that could accommodate a really large head imply something vastly different from humans.
Two examples come up in Ancillary Justice. The Rrrrrr are described as snake long, furred, and multi-limbed, and speak in growls and barks. While certainly alien, they at least seem to be relatable. The Presger aren't described physically, but they are implied to be even weirder and are explicitly stated to use a completely alien logic.
H. G. Wells' The War of the Worlds was the Trope Codifier, particularly for the common "cephalopod alien" variant. Wells designed his Martians by starting out with a humanoid, then eliminating all organs (limbs, digestive tract, etc) that he felt advanced technology would render useless and/or inefficient.
"A big greyish rounded bulk, the size, perhaps, of a bear, was rising slowly and painfully out of the cylinder. As it bulged up and caught the light, it glistened like wet leather. Two large dark-coloured eyes were regarding me steadfastly. The mass that framed them, the head of the thing, was rounded, and had, one might say, a face. There was a mouth under the eyes, the lipless brim of which quivered and panted, and dropped saliva. The whole creature heaved and pulsated convulsively. A lank tentacular appendage gripped the edge of the cylinder, another swayed in the air. Those who have never seen a living Martian can scarcely imagine the strange horror of its appearance. The peculiar V-shaped mouth with its pointed upper lip, the absence of brow ridges, the absence of a chin beneath the wedgelike lower lip, the incessant quivering of this mouth, the Gorgon groups of tentacles, the tumultuous breathing of the lungs in a strange atmosphere, the evident heaviness and painfulness of movement due to the greater gravitational energy of the earth—above all, the extraordinary intensity of the immense eyes—were at once vital, intense, inhuman, crippled and monstrous. There was something fungoid in the oily brown skin, something in the clumsy deliberation of the tedious movements unspeakably nasty. Even at this first encounter, this first glimpse, I was overcome with disgust and dread."
Michael Swanwick's novella "Slow Life" describes an encounter of a human expedition with a hive intelligence underneath a methane lake that is bewildered to encounter a mind separate from its own: "Are you me? Why? Why aren't you me?"
In Revelation Space universe, every alien is a Starfish Alien. The Pattern Jugglers are semi-sentient algae-like aliens that inhabit water worlds, and function like a living library. The Grubs are grublike aliens that hide between solar systems in tiny ships to avoid extinction by the Inhibitors. The Inhibitors are 'post-sentient' Transhuman Aliens which wipe out all space faring races in order to save the galaxy during the Andromeda galaxy collision in a few billion years. Humanity is exactly the kind of problem that the Inhibitors were designed to solve, ergo, all of the non-starfish (i.e. similar to human) species that do things like build cities, launch colony ships, etc now exist only as fossil records have been wiped, while the ones with radically different physiology, psychology or both often still exist since they don't fit the criteria. Thus, outside of us, it's pattern jugglers and shrouders all the way down.
The Oankali in Octavia Butler's Xenogenesis/Lilith's Brood trilogy...some of whom have been genetically altered to be more-or-less humanoid in outline. In their original state, they more closely resemble giant sea cucumbers.
In Sheri S. Tepper's works, one of the odder aliens and alien lifecycles occurs with the "Foxen" in GRASS, the first book of the Arbai trilogy.
The Outsiders from Larry Niven's Known Space series are unaging, near-incomprehensible, Helium-3 creatures that can only survive in deep space at near zero kelvin. Many other aliens are this way, such as the starfish-like Jotoki who start life as a group of five wormlike swimmers and merge head-first to grow a single brain while maturing; the Grogs, cone-shaped beings who are immobile and use telepathy to lure small animals into their mouths; Pierson's Puppeteers, a race of innately cowardly herd animals with three hoofed legs, a brain in their backs, and two snaky heads who use their mouths and tongues as "hands"; and the Jinxian Bandersnatch, a limbless sentient slug the size of a freight train.
This is practically Larry Niven's trope. He has the Draco Tavern short stories, all the Known Space aliens, and the asymmetrical Moties from The Mote in Gods Eye (which he co-wrote with Jerry Pournelle).
The Taurans in Joe Haldeman's novel The Forever War. Their minds are far more alien than their vaguely-humanoid bodies.
Many of the Cthulhu Mythos creatures were, basically, aliens so alien to human comprehension that they became almost mind-snapping by default. Some really were deity-level beings, but others were recognizably just aliens, with cultures and societies akin to humans, just... really not. These include the Mi-Go, the Great Race of Yith, The Flying Polyps, the Star Spawn of Cthulhu and the Elder Things from At the Mountains of Madness. Lovecraft tended to play on the assumption that human sanity isn't strong enough to deal with confronting creatures from other worlds or dimensions.
The Elder Things are quintessential starfish aliens, resembling a tentacled barrel with five pterodactyl wings and a head at one end resembling, you guessed it, a starfish, but in the end even they are seen as relatively "human", at least when compared to the Mi-Go. The Shoggoths, their Servant Race, are just plain terrifying, while the unrevealed Ultimate Evil behind the even bigger and more insane mountains beyond their realm is something even they were horrified of.
Mi-Go are bat-winged multi-limbed fungus-crustaceans, Yithians as usually depicted wearing — and reproducing in — the bodies of towering, trumpet-shaped tripod beings that already lived on Earth when they immigrated via mass mind-swap. Of all of them, only the Elder Things and the Yithians are made of "ordinary" matter; the Polyps aren't fully visible, the Mi-Go don't show up on photographic film and Cthulhu and his ilk are capable of quickly regenerating from any sort of damage.
The Flying Polyps, historical enemies of The Great Race of Yith, are something of a species of Eldritch Abominations. They come down on planets in order to feed, and are described as having "temporary lapses in visibility" by virtue of not being wholly material. They're also Nigh Invulnerable to physical harm; the Yithians defeated them with energy weapons. As for the Star Spawn, the fact that they are merely slightly scaled-down versions of bona fide Eldritch Abomination Cthulhu speaks volumes about their abomination status.
The most extreme of these would be the eponymous "colour" from The Colour Out of Space, an extraterrestrial so alien that nobody realized that it was alive until it finally departed.
Very consciously applied in Wayne Barlowe's illustrated novel Expedition. Barlowe is vocally sick of Human Aliens and Rubber-Forehead Aliens and set out to create the most genuinely alien creatures he could think of. It helps that Barlowe has a background in biology, and he describes the ecology of the world in Expedition in detail. Very few of them have the number of legs one would expect, only one named creature has eyes (and it is a single, atrophying eye at that; the creature seems to prefer keeping it retracted into a special chamber anyway), and only one named creature has anything resembling a conventional head with a "mouth" and "jaws" - and it turns out that the lower jaw can separate from the upper one and that it functions more like a mosquito's proboscis. And yet, he still keeps them familiar enough in subtle ways. There is also an alien of humanlike intelligence — and it is humanoid in only the most subtle of ways. An Eosapien looks more like what would happen if an octopus hitched a ride on a hot air balloon.
Barlowe also painted portraits of many fictional alien races in his Guide to Extraterrestrials and Guide to Fantasy, focusing on very alien aliens including the Elder Things and Velantians mentioned on this page.
Alex Ries, a fan of Barlowe follows this with similar alien designs, one set based on nematode physiology with multiple limbs, you can check out his work at his online portfolio.
Nemo Ramjet (who, by the way, has the best name any sci-fi illustrator could hope for) is another Barlowe fan and has created the very alien ecosystem of Snaiad. Most Snaiadi 'vertebrates', have 2 'heads'. The upper head, the one that looks more like a head, to Earth-based perceptions? It's their genitals. The lower head, which looks like a set of genitals is actually their "mouth".
Korean illustrator Dong Hwa Moon (dilblo) does lots of these in 3D using ZBrush, see more at his blog.
The last book of the His Dark Materials trilogy had a species from an alternate version of the Earth called the "Mulefa" who have a diamond shaped skeletal structure instead of a spine. They also evolved to have elephant like trunks and the hooks on their feet to allow the use of what are essentially giant pea pods as wheels on their front and rear legs, since the viewpoint character for this subplot notes that it's impossible for a species to evolve wheel-like appendages. (If this is hard to visualize, here◊.)
The latter books of Ender saga (once you get past the Child Soldiers part) are pretty much all about the intricate moral distinctions between incomprehensible starfish aliens and Human Aliens - so much so that the series uses its own terms for the two: varelse and ramen respectively. The first species humanity encounters, the "Buggers", seem like clear-cut Hive Mind evil varlese - until it turns out that they only genocided half of humanity because they didn't realize mankind was sentient. Later, in Speaker for the Dead, the "piggies" have such an alien biology, it starts an interplanetary incident before the xenozoologist protagonists figure out what's going on. Also, in Xenocide, it is revealed that the piggies, after dying, become father-trees, and in order to do that, they absolutely require the "descolada" virus, which is lethal to humans (although the "recolada", the crippled version, works just as fine).
There are so many of these in the Old Man's War series that new recruits for the Colonial Defense Forces have to be specifically warned that non-humanoid doesn't mean evil. Revisited and played with in the later books of the series.
The single-celled, collectively intelligent, abyss-dwelling Yrr from the novel The Swarm. The novel goes out of its way to enforce this trope, in fact.
The scramblers in Peter Watts' Blindsight are starfish-shaped, with a reproduction cycle inspired by jellyfish (not surprisingly, Watts is a marine biologist). Their metabolism is similar to that used by anaerobic bacteria (except part of it involves quantum tunneling), they have no DNA, and evolve by selectively killing off individuals that cause problems for the rest. The best part? They're extremely intelligent, but not self-aware.
The T'ca, giant snake-worms with five-part radial symmetry. They speak in "sentences" which consist of a rectangle of words five columns across and an arbitrary number of rows down. The same "sentence" can be read horizontally, vertically, and diagonally, with all three readings be equally valid at the same time. This is because they have five brains; the relation between words on the matrix seems to represent the interaction between their brains to create a unitary consciousness.
The Chi, hyperactive bundles of neon-yellow sticks.
The Knnn, snarls of black hair mounted on spider legs. None of the oxygen breathing aliens have figured out even the tiniest portion of their language, forcing them to use the T'ca as translators. Not that having translators seems to be much help, since the Knnn are so alien that they have yet to be made to understand such simple concepts as "you're going the wrong way down a one-way street". They used to force their way onto dock and take what they wanted; through painstaking negotiations with t'ca intermediators, the concept of 'trade' was conveyed to them. Now they force their way onto dock, take what they want, and leave some other randomly chosen item behind.
In Uplift, few aliens are bipedal. There's one species that looks like a stack of wax doughnuts, another with five-point radial symmetry, and one species that has wheels. The other orders of life are much stranger, including quantum entities and intelligent memes.
The Creapii in The Dark Side of the Sun, which are "sexless, octopoid", need a lot of heat to survive, and travel around in small egg-shaped exoskeletons when they want to interact with humans. They're good at that. And a rather hospitableplanet-sized semiconductor-based brain, with proportional intellect, multitasking ability and energy supply.
Both the Creapii and the planet are classified in-universe in terms of humans, as are phnobes and drosks. Dom briefly mentions other races like the Spooners and Jovians, who are so far removed from humanity that there can be barely any meaningful discourse with them. And of course, there are the Jokers.
Near the end of the book, Ig hints that there are stranger things still in the depths of interspace:
"How blithely you use the word alien; you have no idea how alien a thing can be."
Strata references this - though the protagonist's Kung and Shand alien friends are civilized, and can speak English, they are still alien no matter how familiar they look. Played more straight with the Efht race, which both look and sound like stereotypical Starfish Aliens.
The Trolls in Discworld kind of fit, because while they 'look' like Humanoid Aliens their physiology is geological rather than biological. The troll brain is silicon, so they get stupider in warmer climates and more intelligent in colder ones, and they view the past as being "in front" of them because you can see it, so people travel backwards through time.
There's a bit in Lords and Ladies about how strangely elves perceive the world, apparently via a sensitivity to magnetism.
Various alien species in E. E. “Doc” Smith's Lensman series, including but not limited to the Palainians, who lived on Pluto-like planets and had metabolic mechanisms which extended into the fourth dimension in order to work, the Rigellians, who looked like large barrels on legs with 4 multiply-subdivided tentacles equally spaced around them, and the Eastern dragon-like (to an extent - they have an undetermined number of eyes (but more than eight), each of which is on a stalk, among other oddness) Velantians.
A group of entities indescribable by, or to, man stood, sat, or slumped around a circular conference table. Though they had no spines, they were something like porcupines; though they had no tentacles, they reminded one of octopuses; though they had no wings or beaks, they seemed similar to vultures; and though they had neither scales nor fins, there was definitely something fishy about them.
Diane Duane loves including this trope in her Star Trek novels, adding such members of the Enterprise crew as giant snowflake-shaped silicon creatures, a bipedal catlike being who doesn't comprehend past tense, two-meter-long lizards, a Starfleet captain who is basically a giant slug, a glass spider with twelve legs who wrote the laws for a universe, and —yes— a Horta lieutenant (basically a sentient lump of rock that looks like a giant pizza). The Federation gets a lot more multi-cultural when she's writing. And that's just in Starfleet - she also introduces such species as sentient rocks who can manipulate time, creatures who are basically intelligent amoebae, and trees with a consciousness.
See also her Young Wizards series. The first book involves an intelligent stellar body and things get crazier from there.
The novel The Leaves of October by Don Sakers mostly revolves around a race of sentient, telepathic (but not epileptic) trees that can influence the evolution of other life forms by blowing themselves up. They can also communicate by altering the coloration of their leaves, which humankind does eventually learn to translate.
The Sarlacc is further elaborated on. Scientists argued on it being an animal or a plant, eventually settling on crustacean. It colonizes alien planets with spores launched into outer space. The Tatooine one is a titanic sessile predator that manages to survive the sparse ecosystem of a desert environment by digesting prey unbelievably slowly. It keeps its swallowed prey on messy biological life-support while it digests them, so it can literally feed upon their psychic and physical torment and pick out the choicest neurological morsels to absorb into its consciousness, which it generates from the collective minds of its captive nourishment. It has a nightmare digestive system that rather neatly encapsulates the concept of hell as a living organism.
That giant space slug that ate the Millenium Falcon in The Empire Strikes Back? Xenobiologists believe the Exogorth was once the dominant life form in the galaxy and that the ones they see today are the last remnants of this once-great race. No one has any clue where they came from or what happened to cause them to fall. To quote Arkoh Adasca:
"They're the last remnant of a species that predates history—an unlikely being, if ever there was one. No one knows how or why they evolved—just that we have found a number of them in the galaxy, going about their business... Time has no meaning for such a creature... We thought for a time that they might have once been plentiful in the galaxy—and the ones we find now are the only ones left."
Another notable Star Wars example would be the Shard, a race of sentient, luminescent, immobile crystals that communicate exclusively via some kind of electromagnetic resonance. They grow in clusters and share a kind of group mind, spending their unmoving existence immersed in deep contemplation. However, it's possible for a single Shard to be cut free from its "siblings" and live as an independent organism with a droid body, after which they begin to rapidly develop individuality and more "human"-like personalities.
Galaxy of Fear has a planet that somehow, thanks to mad science, is alive and eats people. Elsewhere there's another living planet, but D'vouran is much less human, for lack of a better word, than Zonoma Sekot. It never communicates in words, but seems to have a degree of intelligence: it takes prey slowly and carefully, hides evidence so they won't be spooked, and supports the symbiotic/parasitic Enzeen so that they'll do whatever they can to induce more people to visit and stay.
The Cheela in Dragon's Egg, by Robert L. Forward: small sentient slugs with twelve eyes on stalks, living on the surface of a neutron star. Their bodies are made of degenerate matter, so despite having about the same mass and physical complexity as a human, they are only about as large as a sesame seed. Because nuclear reactions happen much more quickly than chemical, time passes for them much, much faster than for humans. For all of that, their history and psychology have many similarities to humanity's.
The Tralfamadorians from Slaughterhouse-Five experience time in a non-linear fashion, and as a result have an entirely different concept of literature, which details many unrelated moments, and is ultimately incomprehensible to humans. They're also shaped like plumber's friends topped by hands, each with a single eye in the palm.
In David Gerrold's The War Against the Chtorr novels, mysterious plants animals and viruses from another planet are choking out and dominating the Earth's own ecology. The only reason humans call them "Chtorrans" is because that's how we perceive the sound made by the most dangerous of the new ecology: The giant furry man-eating gastropedes. The protagonist experiences quite a bit of this mysterious new ecology firsthand, including a "storm" of fibrous spores that covers part of California in what looks like 15 feet of cotton candy.
The Sector General novels have an entire alphabetized classification system to describe the tremendous variety of metabolisms, body types, and environments of alien species. And even then, they often run into lifeforms that defy classification.
Jack L. Chalker's Well World series had numerous beings ranging from those that looked like Mix-and-Match Critters (the last set of creators ran out of ideas and cribbed from each other), to the totally alien. The creators of the Universe resembled giant human hearts with tentacles. The Dreel are the Hive Mind of a sentient disease. The North Zone species ...were far weirder than that.
And then there's the colorful collection of aliens from his Quintara Marathon novels, particularly an actual race of Starfish Aliens, the Durquist.
Chalker also has fun with technically non-alien post-humans in the Rings of the Masters series. A Skynet-like AI has conquered humanity and used genetically modified humans to colonize the galaxy. Even though they are technically human, some of them get very weird, including elk- or cattle-like people that grow horns and become quadrupedal when pregnant to protect their stomachs.
The aliens from Robert Forward's Rocheworld series are very nonhuman — the Flouwen are aquatic blobs who love math and surfing and can compress themselves into rocks to think more effectively, the Gummies are elephant-sized five-limbed creatures who put down roots during the dry season and shed an arm during mating, and the "green giants" from the less than spectacular "Marooned on Eden" are mobile trees with detachable birds for eyes and racoon-like "gatherers" for hands.
There are also sentient colored fungal mats with eyestalks. The humans are puzzled by their seeming lack of reproduction (their population grows because the aliens often find feral individuals out in the tundra and bring them back to society), until they finally piece together how it works. A common species of shark swims about the ocean and moves towards volcanic vents near the end of their life cycle. Their corpses are blasted onto the tundra (the world is covered in ice, with oceans underneath) and then their ovaries develop into sentient fungal mat creatures. The sharks are born when the fungal mat creatures find a shark corpse on the tundra, eat its ovaries (a rare delicacy), and a few days later they get violently ill and dump their fertilized sewage into the ocean.
In Stanislaw Lem's Solaris, the eponymous alien is not only a planet and a liquid, but also his thoughts are so different from humans', that the scientists investigating it are going crazy. Also, presumably, various phenomena occurring on the planet are its mind processes, leaving the question of how do the scientists not mentally injure the planet by doing research. It is also possible, that in fact the planet does investigate humans.
In Lem's Fiasco an interstellar expedition which spares no expense, even causing the break up of a moon of Saturn, goes to another star system to contact a race at a similar technological level than them, but they're so alien that communication is extremely difficult. By the end of the book you have a better idea of what the aliens look like (living mounds, maybe colonies of insect-like beings), but it's still not completely certain.
The Strugatsky Brothers occasionally introduce very, very alien aliens, notably a sort of planet-wide microbial colony that has drastically changed the biosphere of its planet and endows its human child captive with the ability to faithfully reproduce any sound that he has heard.
The Nar of Donald Moffitt's Genesis Quest resembled two starfish on top of each other, had five-sided symmetry, communicated by feeling each others' cilia (although they had a verbal "small language" for less-complex distance conversations), and lived a thousand years before changing sexes and reproducing underwater. Their difficulties in understanding human psychology is what leads to the violent climax of the story.
Moffitt's The Jupiter Theft featured the trilateral/radial, brutally utilitarian, and effectivelyall-female Cygnans. And an unnamed race that looked humanoid (and cute, and harmless) ... but, while more sympathetic than the Cygnans, was nonetheless dangerous. Aside from being predatory and having needle-sharp teeth, they could kill by causing acute allergic reactions.
Legacy of the Aldenata has the Posleen, described as hermaphrodite crocodilian centaurs, the Tchi... erm, crabs, which bear a very superficial resemblence to the earth arthropods they're nicknamed after (because the real name isn't really pronounceable with a human mouth), as well as the Himmit, which are basically double-ended frogs with a natural Invisibility Cloak.
Karl Schroeder's Permanence has aliens so weird, they can't talk to humans or other species without an artificial intelligence. This applies to writing as well, and the translations are never anything close to perfect. In the backstory, one intelligent species inhabited an entire planet, forming all living things there. The animals, plants, fungi, bacteria, etc were all one species, and had identical DNA. The scientists thought this was odd, until they found some human babies with the same DNA! (The babies basically had a human mind and an alien mind, which didn't communicate with each other.) When they managed to communicate to the aliens that they were sentient, the aliens responded violently, as they felt no species had the right to alter their environment. The humans had to quickly evacuate and nuke the planet. Other nearby planets were also inhabited by the aliens, and the human colonists there had to leave really slowly before the aliens could catch on to what was happening. Creepy.
In Poul Anderson's Starfarers, one of the sentient species is an intelligent layer of star. Not the whole star, just part of its skin.
Diaspora features several very strange Starfish Aliens. In particular, the first aliens encountered by the descendants of the human race - floating algae mats whose method of reproduction produces, as a side effect, what amounts to a huge biological computer (based on a real type of formal system), simulating a 16-dimensional universe inhabited by sentient squid-things.
A second example from Diaspora is Orlando's story. A professional translator, he has to have himself cloned and modified multiple times, each version of himself translating for the next, to communicate between the post-humans and the first sentient aliens they encounter.
Schild's Ladder features another Universe that contains life. Said life, ranging from non-sentient fauna to sentient beings with their own civilization and technology, exists at the Planck scale. (Mind-bogglingly tiny, for those of you not familiar with the term.)
The people in Orthogonal live in a universe with different physics (you make energy by emitting, rather than absorbing, light), and their biology is similarly weird: they reproduce by fission, they extrude extra hands as needed, and the only thing they need an atmosphere for is to avoid overheating.
Isaac Asimov's novel The Gods Themselves is unusual for an Asimov book in that it does feature aliens, instead of just humans and robots. There are two species, living together on a planet in a parallel universe, known as hard ones and soft ones. Neither are physically described in much detail, but the soft ones are apparently amorphous or gas-like, have three genders, and appear to be photosynthetic. The hard ones are three soft ones united during sex, acting as an independent being. Asimov joked he created them because someone complained there wasn't enough sex in his stories, so he made three.
Asimov seemed to love this trope. Let's see: 1) Horse descended aliens which need hydrogen cyanide in the air they breathe, and who cannot understand marriage. ("Hostess") 2) Sulfur based life forms which cannot understand how humans can have more than one government. ("In a Good Cause—") 3) Chlorine based creatures which evolved from something like insects, who cannot understand how a group of humans found together can be anything but a social group connected more deeply than a family. ("C-Chute") 4) A Hive Mind which can design parts of itself to look like anything, including pieces of wire, and which is desperate to make Earth similar to itself. ("Green Patches") 5) Tentacle horrors from a dying planet who are seriously disturbed by the fact that humans can feel emotional connection to their children. ("The Deep") 6) Bug eyed monsters who cannot understand the idea of sexual reproduction. ("What is This Thing Called Love?")
In Gregory Benford's The Sunborn humanity discovers strange alien gas-bags on Pluto when some of them start feeding off of the heat given off by their probe. Said alien gas-bags have sapient intelligence. And then a bunch of robotic drones descends on Pluto apparently eating said aliens. These robotic drones turn out to be the equivalent of microscopic instruments used by what is apparently an intelligent race of electromagnetic waves.
Benford's Against Infinity has an alien entity called the Aleph, which is even weirder.
The short story The Very Pulse Of The Machine by Michael Swanwick has a lone human astronaut on Io who begins hearing voices in her radio. She may be hallucinating but it's strongly suggested that they're real, and if they are, Io itself is alive and talking to her via electric currents in its crystallised-sulphur surface.
In Robert J. Sawyer's Calculating God, the first alien met by the main character is a big spider-sphere thing. That alien also takes a few shots at the Rubber-Forehead Aliens on Star Trek, when he is being introduced to human culture.
Iain Banks' The Algebraist has aliens that resemble tumbleweed, pure energy beings, sentient nebulae, and a several species of creatures that live in the atmospheres of gas giants, some living for billions of years.
The Tangled Strings of the Marionettes by Adam-Troy Castro has the Vhlani, who resemble black spheres with eight whip-like tentacles. Humans have great difficulties understanding their language, which consists of "dancing". Some humans are trying to learn the language via extreme body modification, but as the title alludes, they only have limited success.
A Fire Upon the Deep has the Tines, a race of seal-headed dog creatures that communicate through ultrasound that is so fast and complex that it might as well be telepathy. Each individual Tine is nonsapient, but when four or more combine they become an intelligent individual. However, the ultrasound interferes if too many Tines get close together, so when the number of single Tines in a group exceeds eight they start to get dumb again. As a result a civilization of "individual" packs of around 3-8 Tines has grown. Some individuals live for hundreds of years as they gradually replace members that die (and if both parents of the new member also belonged to its new collective, the collective's personality is supposed to stay exactly the same). A lot of plot points hang on their unique physiology. For example, one of the villains attempts to escape his enemies by literally splitting himself, murdering parts of some of his dupes and merging his constituent Tines into the remnants of their collectives, intending to recombine them back into himself, once out of the danger zone. He succeeds... partially.
There's the Skroderiders, sentient sea-lily creatures with no short-term memory that ride around on computerised wheelchair-like skrodes.
There are also the Powers - beings who live in the Transcend, and have crossed The Singularity (a term of Vinge's coinage). By definition, they're like Starfish Aliens, minus the anthropomorphism. In the Beyond, school kids study them in Applied Theology.
In A Deepness in the Sky, he created the Spiders of the On/Off Star, giant arachnoid aliens that hibernate every few decades when their star goes into a cool period. They are more human psychologically than the Tines though, or, at least, they seem so, because the spider sections of A Deepness in the Sky are supposed to be texts written by human researchers, who used Translation Convention, while Tines interact with humans directly from the beginning.
One of Vinge's greatest alien races are the Shimans from the story "Original Sin". They are kangaroo-like in appearance and highly intelligent, but they only live for two years before they become asexually pregnant with voracious babies that eat their way out of their parents. They retain that incredible hunger all their life and have a terrible time building a civilization without eating their coworkers. The only way they succeed at all is that they are smarter and more energetic than humans. One of them remarks to a human that humans are lucky because they are naturally good, whereas Shimans have to work very hard to be good.
In Anne McCaffrey's Petaybee series, the planet Petaybee was 'awakened' through the terraforming methods used to make the planet habitable by humans and communicates with its inhabitants through hallucinations that are given through a network of special caves. The first several books hinge around the Company who terraformed the planet trying to recoup its investment and the inhabitants' efforts to convince them of the planet's sentience.
In Animorphs, you have the Taxxons, which are essentially gigantic worms with a zillion rings of teeth, extra-long prehensile tongues, and a buttload of claws and legs. Their mouth structure makes it impossible to speak the common language of the galaxy, and they are beholden to an uncontrollable hunger that will result in them eating even themselves if they are injured. They are played in a more sympathetic light after Ax and Tobias both morph into them at one point, and ally with Jake as part of his final strike against the Yeerks in exchange for morphing technology in order to trap themselves in forms that aren't enslaved by their hunger: large, Amazonian snakes.
The Yeerks, a race of parasitic slugs that burrow into the ear of their hosts to infest and take over their brains, feed off of energy from their home sun, and reproduce though some sort of fusion/fission ritual that kills all three of the parents. In their natural state they're completely helpless and have no form of communication outside of their own species, despite being intelligent and entirely sentient.
The Andalites have no mouths, eat by absorbing food through their hooves, speak using telepathy, have four eyes, can see in multiple spectrums, have incredibly precise internal body clocks, and have three hearts.
The vast majority of the alien species in Animorphs. Leerans (psychic giant yellow frogs with 4 tentacles instead of arms who can easily survive half of their brains being removed and go on to regrow them), Hork-Bajir (7 foot tall 'walking salad shooters' with blades everywhere who eat tree bark, the Arn (a race of hyper-intelligent things that look sort of like squirrels, with gemstone eyes and wings), Skrit Na (aliens who go through two life cycles, the 'skrit' where they look something like giant cockroaches and then the 'na', where they take on a more conventional appearance, that of the stereotypical alien 'grays'), Veelek (a combination of microscopic creatures who travel in swarms), the Nesk (intelligent alien ants who swarm together to create constructs that look a little more conventional), the Helmacrons (each about 1/16 of an inch high, who have 4 legs and triangular heads and whose brains are absorbed by the rest of the species when they die)...
Also by K.A. Applegate, the Remnants series features different alien species, of which the Squids are the most normal. The Blue Meanies/Children are described as looking like giant cats with tentacles they use for sign language, the Riders have two different-looking heads (one is basically just a mouth), and the Shipwrights look like starfish, but with transparent skin. Squick.
A third Applegate series is Everworld. While a fantasy novel, two "alien" species are mentioned: the Coo-Hatch and the Hetwans. The Coo-Hatch are a weird race specializing in metallurgy; the large adults are often followed by strange little bugs which the characters guess may be their larval forms. The Hetwans are like giant flies whose males rip their partners apart during sex, the babies somehow being born during the process. (Also, they worship an Eldritch Abomination who wants to eat all other gods.)
The StarBridge series of young adult novels by Ann C Crispin has any number of these aliens. The dominant (though peaceful) aliens of the galaxy are giant snakes, which preside over a menagerie of alien forms. The strangest one is most likely the race of amorphous blobs that communicate only through vibrational pulses, although the blanket-sized telepathic fungus alien that remained a major recurring character for most of the series got more screen time.
Bruce Coville loves these. His best-known series, My Teacher Is an Alien, features a cucumber-like alien that communicates by popping scent-filled pimples, and the ship's captain was an intelligent crystal formation. His Rod Albright series has Tar Gibbons (member of a multi-gendered species), Phil the Plant, and Edgar/Seymour (member of a symbiont species which splits into two bodies as part of its life cycle). On the psychological side, Captain Grakker uses a computerized implant to experience moods.
Frederik Pohl's The World At The End Of Time features plasma-based aliens who live inside stars and don't care much for "slowlife" like biological beings.
Eric Nylund's A Game of Universe features some weird aliens, like an alien who is a colony of several insect species living in symbiosis, or beings who live in molten rock and protect their mineral resources by magically exploding any mining ship to approach their planet.
The Black Cloud by Fred Hoyle is about a sentient nebula-sized entity made of ionized gas.
Then there are the sandworms of Frank Herbert's Dune series, which are gigantic (as in up-to-half-kilometer-long) wormlike creatures that live in the desert. They begin life in several larval forms; starting out as a microbial "sand plankton," called "Little Makers," that serve as food for the adult worms. These eventually grow into a small, roughly diamond-shaped form called Sandtrout. The Sandtrout are later revealed to seal away all water on the planet, making them highly toxic to the hydrophobic adult form, and secrete the precursors to the addictive and Psychic Powers-granting spice, Melange.
Most of the aliens in Mark Crilley's Akiko books are simply cartoonish humanoids, but one of the recurring characters, Poog, is a purple-skinned floating head with extremely powerful Psychic Powers.
All of the aliens in T. Jackson King's Retread Shop are starfishy. One of the main characters is a many-tentacled, many-eyed, telepathic plant alien. The villain is a Tet, a four-armed giant salamander. Other species include the Dorsellians (a species of flying manta ray-like beings), the Hecamin (which resemble lions with manipulatory tentacles for manes, and have some sort of insufficiently-explained Bizarre Sexual Dimorphism), the Bareen (numerous furry, spherical beings that combine to form "clumpings"), the Melanin (another species of Plant Aliens, this one photosynthetic and resembling a levitating shrub with one eye and an elephant-like trunk) and the Chellaquol.
The Bible describes angels as having bizarre appearances or as being easily mistaken for humans, never anywhere in between. The former cases (eye covered wheels being among the most mundane) are apparently horrific they introduce themselves with "be not afraid". Some having hundreds of hands along with multiple layers of heads, speaking fire, talking winds, "amber/electrum coloured" lights or beings so bright they have to be covered with multiple pairs of wings to prevent Earthly onlookers from dieing.
Ben Jeapes' "Commonwealth" triolgy has the First Breed, dubbed the Rusties - four-legged aliens with tentacles near their mouths. Their language sounds like someone being strangled, so they use translators instead. Untranslated Rusties Language has the emotion in square brackets first, then the sentence in double triangle-brackets. [Explanatory] <<Like This.>> They have no imagination - they were raised from primitive cattle beings by the Ones Who Command, who treated them as labour and cannon fodder. The Ones Who Command accidently sterilized themselves with a virus, and now only the Rusties are left. They have weird ideas about leadership.
The Xenocide Mission has what are known by humanity as XCs, short for "Xenocide" as there used to be another species in their home system, but as soon as they discovered their existence they nuked the planet to hell. They have four arms and two legs, can share memories by cutting off "shareberries" that grow from the back of their necks and eating them, and hibernate for half the year after which they temporarily lose their sentience until they kill and eat something. For obvious reasons the Rusties crossed them off their list of potential replacement Ones Who Command. Then the protagonists meet remnants of the neighboring species and discover that they telepathically drain sentience from XCs, when their planets came close to one another the XCs would fight brutal wars with one another, the xenocide was in self defense.
The Quarn in In Fury Born (an expansion of Path Of The Fury) are almost literally Starfish Aliens, being described as "a radially symmetrical cross between a hairy, two-meter-wide starfish and a crazed Impressionist's version of a spider". No matter their physical appearance, they get along with humans quite well. This is mostly due to the facts that both species 1) find the other's planets all but uninhabitable (helping prevent territorial warfare), and 2) share a love of biological/reproductive humour.
Tais Teng's aliens tend to fall squarely within this category. Examples of note include various species of organic spaceship, the Wessyn Engineers (something like bus-sized beetles, but with technology that allows them to build on a stellar scale and slip into a two-dimensional state), a species thriving on planets where the surface temperature approaches zero K, and the giant Lespadin who are used by another alien species as walking cities. It is implied that the few species really worth meeting have already achieved Enlightenment, becoming superior beings that mere humans cannot communicate with. What remains of the universe is "just another ghetto".
The alien species in Paul Harland's Water to Ice. Some are so strange and ancient that nobody has a clear idea of what they are at all. The Kysx, for instance, are flying balls of fuel and fire, said to have arrived in spaceships half a meter in diameter and two kilometers long. The Rrith have the body of a ray and communicate by shifting the pattern of the fur on their back. The Ftott are big sponges whose limbs are blades of bone; they "talk" by hacking specific parts off their opponents...
The Sten series features occasional wildly nonhumanoid creatures, such as the peaceful race of floating jellyfish, or a ring of sentient polyp creatures that appear to be permanently installed in a ring inside a large Customer Service desk. There's also one literal example of a Starfish Alien, and it's nightmarish for three reasons: it's as tall as a man, it runs through waist-deep water as quickly as a man can on land, and it's got a thresher maw in in its center. The creature, called a "gurion," is only encountered once in the series but remains one of the most memorable and horrific of all the alien entities Sten fights.
Robert A. Heinlein's Stranger in a Strange Land is a little vague about the nature of Martians, but they seem to be giant, globe-like fur-covered creatures who have go through a multiple-stage full body metamorphosis several times in life before eventually becoming just disembodied psychic entities. Their mode of thought is so different from that of humans that the Martian-raised protagonist's struggle to understand even the rudiments of human mentality are the nucleus of the book's entire conflict.
A Martian's life has four stages: egg, nymph, adult, and Old One. All adults are male, all nymphs female: like some Earth fishes and amphibians, all Martians go through both sexes. Competition and rivalry happen solely among nymphs; the adult stage are so pacifist that even an awkward social situation might cause them to discorporate, shedding their bodies and becoming disembodied Old Ones. Oh, and all adults and Old Ones are incredibly powerful telepaths and telekinetics. And cannibals.
The Martians in Red Planet are similar in nature and lifecycle. The description of those in The Rolling Stones is less detailed since they are incidental to the plot so it is hard to determine their similarity.
While Heinlein did do humanoid aliens, he also mixed it up with stranger ones:
Between Planets: Venusian "dragons". Giant, intelligent, six legged dinosaur like creatures with manipulation tentacles from their necks. The Martians are more humanoid with the description fitting that of The Greys.
Citizen of the Galaxy: While a member of Sisu, Thorby encounters two alien races. The descriptions of the races make it clear they're not remotely humanoid. Their cultures and philosophies are also very alien, to the point that Sisu doesn't even interact directly with one race.
The Masters, the antagonists who drive The Tripods, are tall cone-shaped creatures with three eyes, three legs and three tentacles. Physically they breath thick, green fog, have a low tolerance for ethyl alcohol (which becomes a major plot point later), and an extremely sensitive area between their respiratory orifice and ingestive orifice, making the lightest brush extremely painful. They breathe a thick, greenish gas that is deadly to humans, bathe in near-boiling water several times a day to keep moist, have their own form of drugs, and seem to have only one disease. Psychologically, they are incapable of lying and cannot grasp the concept of fiction or exaggeration (though at least one of them gains a firm understanding of sarcasm), are incredibly tolerant of hardship and difficulty (to the point of becoming ill if they don't work hard), drink gas bubbles as an intoxicant, and die if they're put in a situation they feel they can't escape from (as one master innately committed suicide when captured by the White Mountain Resistance in The Pool of Fire.)
Frank Herbert's ConSentiency series have the Taprisots (sentient telepathic logs which function as a communication system), the Gowachi (semi-humanoid frogs with a legal system so complex it literally defies description), the Wreaves (semi-insectoid humanoids who take insults very personally), the Pan Spechi (who actually live through five different bodies, one at a time) and the Caleban (vast and massively powerful aliens that appear as sentient stars, and it is strongly suggested that every star in the universe is the visual manifestation of a Caleban)
The Host contains the "Souls", a Puppeteer Parasite species. The main character actually comments on how no species they have taken over has been exactly the same. Other species mentioned are basically giant intelligent dragonflies, intelligent flowers, and seaweed with eyes and a psychic connection to the entire species
The Ra'zac are revealed to be Starfish Aliens in the second Inheritance Cycle book. They are unrelated to any other living thing. They have humanoid shapes, exoskeletons, Black Eyes of Evil, and beaks. They are only the larvae of an even worse creature: the Lethrblaka, a huge pterosaur-like creature with the same strange eyes.
The Hrangans, powerful psychics and masters of massive slave armies composed of beings of varying intelligence, of George R. R. Martin's Thousand Worlds Science Fiction stories. They were apparently so alien that communication between then and humans was basically impossible. Even human psychics weren't able to get anything from Hrangans but mental static. At any rate, the Hrangans didn't feel like talking, they were much more interested in conquest.
The short story "Epinikion" by Desmond Warzel features the Squids, militaristic cephalopod-like aliens with unusual funerary rituals and natural weaponry that spells a hideous end for anyone who loses to them in close combat.
Ted Chiang's short story "Story of Your Life" is about a human team's attempts to study and communicate with an alien species. Eventually, the linguists realize that the alien written language is nonlinear because the aliens don't have our idea of time. Learning the alien language enables the linguists to perceive the future, but not to change it.
Polish sci-fi writer Jacek Dukaj has a couple examples in his writing.
The adynatosee in "Different Chants" (an Alternate History with Aristotlean physics and metaphysics) come from outside the sphere of constant stars. In the book every object and beeing has a morph (form) which influences the morph of other objects/beeings near it. Their form is so alien, that people start melting miles away from a city they built in Africa.
Lute (the ice angels) in "Ice" are another example. Looking like a combination of a jellyfish with an ice sculpture they move by melting old parts and frozing new ones. The question whether they are even alive is never answered (though most people think of them as such) but leads the main character to the conclusion that he doesn't exist. Also they seem to have an aura of boolean logic - no uncertainities, quantum mechanics, wave-particle duality or even believable lies around them.
The dragonlike reptilian aliens - just known as "dragons" - in The Pit Dragon Chronicles are not particularly weird to look at, but they're telepathic and communicate in incomprehensible patterns of color, and it's very hard to tell how intelligent they are. So what do the descendents of penal colonies dumped on that world do? Capture them, pen them, and force them to breed and take place in bloody ritual fights, of course! Though this is said to have saved the dragons, as apparently they were dying out, surviving ones being too viciously territorial to know when to stop, and they were carefully bred to be less aggressive. It's still very hard to tell how their minds work and how intelligent they are, even in A Sending Of Dragons, where the main characters can perceive their sendings as words. Then thirty years later came Dragon's Heart, which had Series Continuity Errors to the point where dragons are clearly clever but not mysterious or weirdly insightful at all, and distinctly limited.
David Alexander Smith's In The Cube virtually lives on this trope, with such beings as Koltsoi (huge hideously-ugly beings that "see" heat and move with incredible grace via hydraulic extension of limbs), Targives (never-seen genetic engineers who'll graft new abilities onto people, but always take something unexpected away in exchange), and "popcorn aliens" (oddball traders whose freaky grammar makes them all but incomprehensible). Even the Pfneri, small beaver-like beings who seem superficially familiar, speak a Starfish Language with no verbs, have senses so keen that they can Sherlock Scan and mime events that happened centuries ago, share a Hive Mind collective memory of their ancestors' experiences, and regard death as merely the completion of a story, hence something to find contentment in rather than grief.
The Leviathans living on Jupiter in the novel of the same name by Ben Bova are giant (as in kilometers-wide) conglomerations of independent parts, living in an ocean of liquid water suspended several thousand kilometers deep in Jupiter's atmosphere, feeding on organic molecules formed higher up in the atmosphere. They reproduce by going off on their own, away from the pack and 'disassociating' - splitting into their individual cells, which then split themselves and reform into two new conglomerations, each with identical memories to the original. And they're intelligent.
Star Maker has literal Starfish Aliens: an intelligent species that evolved from starfish-like ancestors. It also features beings that resemble living ships, intelligent insect swarms, and most alien of all, intelligent stars and nebulae.
The denizens of Flatland aren't that difficult to relate with in psychological terms. However, they are physically extremely different. For starters, they are two dimensional objects, consisting entirely of various polygonal shapes. Flatlander men and women are segregated in society due to the fact that female Flatlanders have very sharp edges, and accidentally running into one can result in getting disemboweled. A big chunk of the story results when the narrator ends up encountering their own equivalent of a Starfish Alien; a three-dimensional sphere, which exhibits the ability to move in and out of the two dimensional realm at will and can do such things as poke the insides of our square protagonist.
Most of the aliens in the Star Carrier series qualify. Of the ones revealed in the first two books, the Turusch evolved to live in Venus-like atmospheres and exist as pairs of cylindrical organisms with a Starfish Language wherein each body speaks a separate line and the harmonics between the two lines of dialogue create a third. The H'rulka are colony organisms (think Portuguese man o' war) that form a Living Gasbag averaging 200 meters long and evolved in the upper atmosphere of a gas giant. The most human-like psychologically are the Agletsch, a Proud Merchant Race of spider-like aliens that get drunk off vinegar and treat eating as an intensely private act (which is good, because their method is Nausea Fuel for humans).
Janusz Zajdel's short story "Iluzyt" (about a science-fiction writer who finds a drug which gives a string of story ideas) includes a description of "solipses", plant-creatures which are sapient, but are unable to perceive anything properly with their senses; and so, none of the individuals is even aware of the existence of anything beyond its own mind, regarding all sensory input as hallucinations. Their consciousness also stretches a couple of feet around their bodies, which means that anyone who gets nearby enters a sort of a mind-meld.
Sergey Lukyanenko's The Stars Are Cold Toys duology features anything from Human Aliens (although those are revealed to be cousin races all originating from a common source) and Petting Zoo People (e.g. the rat-like Alari and the mantis-like Hiksi) to truly alien creatures. For example, the Torpp are sentient plasma clouds encased in magnetic bubbles living in star coronas and able to move through space without ships (although it's not clear if they're capable of independent FTL travel). At least two races are worm-like in appearance. One specializes in mining for the Conclave given their natural affinity for burrowing. The other has a mouth with large teeth at each end and doesn't appear to have anything resembling a head or even the concept of "front" and "back". There's a race of living computer lizards (they're revealed to be artificial constructs) and Hive Mind symbiotes able to meld with nearly any biological species and act as Translator Microbes.
Lukyanenko's Spectrum also features some strange races. One is a sentient race of 3-foot amoebae whose homeworld is covered by a layer of water with such a high surface tension that other races can walk on it. However, if they spend more than a day on that planet, they will die from their own body fluids adopting the local surface tension (i.e. blood can't flow anymore). Members of another race live only for six months and die shortly after giving birth (which implies that they can never have a positive population growth). Additionally, they give half their memories to their offspring. Another race looks like The Reptilians, except only their males do. Their females are non-sentient, are much smaller, move on all fours, and are usually treated as pets.
In S.A. Swann's Terran Confederacy universe, the Paralians are described as 'squid-dolphins'. The Helminth are meter-long worms which have technology and build cities, but human scientists are largely unable to communicate with them. The Race are colorless amoeboid blobs.
Some Discworld books have Things from the Dungeon Dimensions, which apparently look like "a cross between an octopus and a bicycle". They're used for Lovecraft Lite storylines, especially in earlier books.
The blob-like rock-burrowing Horta which appears in the "Devil in the Dark" episode of the Star Trek: The Original Series. The episode was written around the already-existing creature-prop, after the operator demonstrated how dramatically effective it could be. The Excalbians from "The Savage Curtain" (different rock monsters), the superheated crystalline Tholians, the huge hundred-tentacled Kelvans in their native form, and the Companion from "Metamorphosis" (a sentient gas cloud) also apply. And the Medusans: Friendly Neighborhood aliens, who get along fine with human beings as long as the human beings don't accidentally look at the Medusans and go raving mad as a result.
From "Ensigns of Command" come the Sheliak, who seem not so much bipedal as merely "upright", featureless except for shiny triangular scalelike extrusions on their skin. The extraordinarily complex treaty they have with the Federation was codified in their language (which appears on-screen as layers of pictograms drifting by at different speeds), since they find Federation languages imprecise. They honor their agreement with the Federation despite the implication that they see humans as idiot vermin.
Armus, the creature that killed Tasha Yar, was a "skin of evil" cast off by a race of "titans." Tricorders and sensors couldn't make sense of it it. It presented itself as a shapeshifting black liquid which could absorb humanoids, use teleportation and other psychokinetic attacks, and inflict serious damage with energy discharges (this is how Tasha was killed). The entity was pitifully dependent on sadism for its own entertainment, and clearly distraught when it learned that it was to be stranded on a barren planet forever.
The cytoplasmic lifeform in "Nothing Human". The Universal Translator can't understand its language, the tricorder can't comprehend its biology, it controls a spaceship via biochemical secretions, can leap through a forcefield in a single bound, and uses B'Elanna Torres as an emergency life-support system. What a guy...err...bug!
Kid Chaos in "The Fight", an entity from a completely incomprehensible reality where the laws of physics are in constant flux. Even with it and Voyager desperate to communicate with each other, Starfleet's best have to make vast intuitive leaps just to deduce its existence, and it can only communicate with them by slowly driving Chakotay insane and then splicing together fragments of his visions.
The ship eating lifeform in "Bliss", the sentient nebula in "The Cloud", and the non corporeal life forms in "The Haunting of Deck Twelve", "Coda" and "Twisted" should probably count as well. Oh, and the Caretaker.
The Q are so different that even the two Q who had spent the most time among humans had to have a discussion on how they were going to represent their realm in terms humans could understand. And even then, the metaphorical representation of the realm was a bit strange (at least it was the first time). They were able to convey the basic point that their society had stagnated and that Quinn felt he'd done everything he could as an immortal cosmic being.
Quinn: I traveled the road many times, sat on the porch, played the games, been the dog, everything! I was even the scarecrow for a while.
Q: Oh, we've all done the scarecrow, big deal!
Star Trek: Deep Space Nine's Changelings were sentient beings made of liquid who lived on a planet, connected together, as one, resembling a living ocean. Odo, however, takes a humanoid form when dealing with humanoids...and resides in a bucket as a liquid for 8 hours a day. The only Starfish alien main character in Star Trek history, though mostly he resembled a Rubber Forehead Alien and rarely shifted in early seasons due to budget limitations and the wonders of 1993 CGI.
The Bajoran Prophets, "non-corporeal" aliens (that is, with no physical form whatsoever) who resided in a stable wormhole and are worshiped as gods by the Bajorans. They communicate to Sisko only through visions in which they appear as people he knows. They exist at all points in time simultaneously, and have difficulty with concepts like "future" and "past". Later seasons also introduced evil counterparts called the Pah Wraiths, which had been expelled from the wormhole.
Star Trek: Enterprise has the Xindi Aquatics, Avians, and the web-like symbiotic organism which temporarily assimilated various crew members in order to provide the collective harmony it needed to survive.
Despite the improbably large number of Human Aliens, Doctor Who also has its fair share of Starfish Aliens, the most prominent of which are the Daleks, who are basically brains with tentacles living inside Powered Armor that resembles floating pepper shakers. Especially the Imperial Daleks, who, amongst other things, had two brains, an exposed spine, and had their organs in a separate chamber. Here, have a look.◊
Whatever they were dealing with in "Midnight": on a planet that cannot support life as we know it, a tourist gets possessed by something that acquires language skills by repeating other people, until it speaks at the same time as them, then before.
"The Eleventh Hour" gives us the Atraxi. They resemble large eyeballs fixed at the center of a large, crystalline web, and are able to travel through space without any trouble. They have incredibly deep, scratchy voices, the ability to hack into electronics, and they hold their prisoners in alternate dimensions. Now that's an alien police force!
The TARDIS herself, a multi-dimensional being of near-godlike power who zips around the time-space continuum whilst disguised as an old-fashioned British police box. Her entire species appears to be cyborgs, raised from coral, able to make psychic links with their users, communicate not in words but feelings, and have their senses distributed throughout the fourth dimension.
On a related note, the House from "The Doctor's Wife." It's an extrauniversal Genius Loci the size of an asteroid that eats TARDISes.
The Fendahl from "Image of the Fendahl": a hive-like, partially noncorporeal alien which included a possessed skull, a floating golden woman and invisible life-sucking slug things amongst its aspects. Other particularly bizarre aliens include the Rutans (glowing tentacled blobs, first seen in "The Horror of Fang Rock") and the Ogri from "The Stones of Blood" (a giant mobile rock that makes a constant heartbeat-like noise).
The weirdest may well be The Shift from the Eighth Doctor novelAlien Bodies, which is a sentient concept who communicates by inducing minor hallucinations (the pattern of bricks in a wall suddenly looks like words, for example).
Other examples from the novels include sentient crystal creatures who shatter their limbs and grow new ones to suit their current surroundings, multiple living planets, a sentient virus that makes humans immortal, and non-humanoid squid aliens who carve obscene graffiti across the surface of the moon after they invade Earth. Also, a tentacle-monster body shape is stated to be the most common in the known universe (including more common than humanoid).
Torchwood: Children of Earth introduces the Four-Five-Six. They're only seen in brief glimpses through a toxic fog, their preferred means of communication seems to consist mainly of shrieking and spraying bodily fluids (their English is spoken through translators), and they bind prepubescent humans to themselves to use their hormones as drugs.
The Stargate Verse is generally very good about making aliens that could not possibly be humans in monster suits. If it is not outright human, then it is about as far from it as you can get, with the only real exceptions being the Nox. They were, of course, were Rubber-Forehead Aliens due to budget constraints in the first few seasons. For a few examples:
The Goa'uld fit this trope to a tee, but you would never know unless you saw the first few episodes until later on. This makes them incredible spies.
SG-1 had the Reetou, who had spider-like lower bodies, eyestalks, and existed out-of-phase from human atomic reality (in real terms, that means "they're invisible without the gadgets the gang invents mid-episode.")
The Unas are Lizard Folk that may be this, depending on the episode and season.
Later on in Atlantis we learn the true origins of the Wraith, which makes them this, rather than the Humanoid Aliens they were.
It also has a non-corporeal black entity in the first season which feeds on energy. As in, ANY type of energy: electricity, body heat... It only appears once and is never explained just how intelligent it is; it's apparently smart enough to recognize a trap.
Stargate Universe introduces two. The Ursini have monkey-like physiology, but that is as far as it goes. The other is the Blue Aliens (the Nakai) that keep trying to take the Destiny.
In The Outer Limits TOS episode "Cry of Silence", a couple encountered a group of aliens who possessed various objects (such as tumbleweeds) and human beings. They tried to communicate with the aliens, but ultimately failed because the aliens' thoughts were just too different.
Occasional characters on Babylon 5, such as the insectoid, methane-breathing crimelord (who was created to try to address complaints about TV sci-fi only having Rubber-Forehead Aliens, but unfortunately the puppet broke). The Vorlons are tendril-covered Energy Beings, and the Shadows, when visible, resemble the praying mantis. In-universe, this isn't really co-incidental thanks to the Vorlons messing with the evolution of most of the younger races.
Farscape has The Pilot, an insectoid literally rooted to Living Ship Moya. The Han-jee, an insectoid creature with tentacle like eyestalks and removable eyes with natural wi-fi. The Proprietor, a giant vaguely crustacean-like creature with lots of claws and fangs. The Ancients, multiarmed, vaguely insectoid. Jotheb of the Consortium of Trao, a green and black, multi-larynxed intelligent being with traits of both a cephalopoid and an insectoid. The Hynerians who are vaguely humanoid but adapted for an aquatic environment (despite being air-breathers) making them amphibious (though whether or not they are amphibious naturally or only with technology like hover-sleds is an open question). The "Serpent" that dwelt inside wormholes. The rather Lovecraftian-looking glimpses of the Interdimensional entity from "Through the Looking Glass". The metallic Boolite, and many, many more.
Blake's 7 had some kind of corrosive life form composed of goo-ish matter bearing an uncanny resemblance to vomit, and a Living Planet that raised some very interesting questions about evolution, metabolism and reproduction.
As does the series Earth 2, which also features symbiotic creatures which are technically humanoid but with a Starfish Psychology. They were underground dwellers who burrowed through the soil like Sand Worms, emitted a trilling starfish language, had scolexes instead of mouths, and were at various times said to either resembles plants more than animals, or to be virtually indistinguishable from the geological composition of their (living) homeworld.
The Future Is Wild: The 200 million years future era features "squibbons", intelligent tree-dwelling land squid that backflip between branches, which may be "the forerunners of a future civilization".
Zini from the German children's series Spaß am Dienstag (Fun on tuesdays). A "Wuslon (pronounced: "Voozlon") from the family of electroids", Zini essentially was a computer-generated yellow-orange circle which would move over the TV screen during the show, dragging a slowly fading "shadow" along. A human speaker lent him his (electronically somewhat distorted) voice, which allowed Zini to interact with the various human co-moderators (no Translator Microbes needed). Later, Zini could also change his size, shape and/or color. See also here.
the Children's TV show "Yo Gabba Gabba" on Nickelodeon in the episode "Superheroes" had an alien named Starsky that the gang help get home with the help of Mos Def.
The Solomons from 3rd Rock from the Sun, despite never seeing their true forms (something about purple tubes). They have no concept of human emotions, culture, or thought processes, which is where all of the comedy comes from.
An episode of Carl Sagan's Cosmos: A Personal Voyage speculates on what aliens might look like if they evolved in the atmosphere of Jupiter. There were the microscopic "sinkers" that rode the wind currents, the "floaters" who were kilometer-wide balloons who fed on the sinkers, and the "hunters" who fed on the floaters and who looked like pterodactyls with bizarre heads.
Anything in the "Unknowns" category of Mortasheen that isn't a flat-out Eldritch Abomination is this, with the strangest being the Meteor Series, which aren't even technically "alive".
The Hivers of Traveller are vaguely starfish-like aliens with nonhuman physiologies, biologies, psychologies, society, and which reproduce by budding. Considered a challenge to role-play. Despite the name, they are not a Hive Mind, nor are they Bee People. The tag "hivers" was hung on them by a human who thought their buildings looked like beehives.
The worm/salamander-like Syllix, the insectoid centaur Vrusk, and various other species, as well as the Kliks and ke'kekt from their other sci-fi property Star*Drive.
Yazirians are arguably Petting Zoo People, but the Sathar and Dralasites might fit. Sathar are sentient, humanoid invertebrates who seem to be a human - sized cross between an earthworm and a squid, and due to their nonhuman psychology are an NPC-only race. Dralasites have surprisingly humanlike personalities but are physically the strangest of all, being fully sapient amoeba-like multicellular organisms, and reproducing by budding.
The Tyranids are a Horde of Alien Locusts with an endless series of bizarre forms and even more bizarre Living Weaponry. The creatures aren't actually individual beings, but instead mere extensions of the collosal single organism that is the Nid's Hive Mind; when separated from it, a Tyranid creature becomes a mindless animal.
Orks look like, well, Orcs at first glance, but are actually closer to sapient, humanoid fungi. They reproduce through spores, are missing several organs vital to most species, are mildly photosynthetic, and every orkoid creature - from the tiny Gretchin to the collossal Squiggoth - are all technically the same species.
Many species that serve the Tau Empire, including the Kroot and the insectoid Vespid. The Kroot are especailly strange, as they evolve by consuming the flesh (and genetics) of other species, assimilating and collecting their traits to direct themselves towards a particular path. The entire animal ecosystem of their homeworld Pech is composed of nothing but Kroot derivatives.
Medusae, an HQ choice for the Dark Eldar, are parasitic creatures that resemble a "collection of brains and spinal cords that are stacked on one another" and use emotional trauma as a weapon.
The saruthi from Eisenhorn are at home in Alien Geometries, have no symmetry, and move in ways that make the title character physically ill just to look at. However they may not have started out this way, as they've spent millennia being corrupted by an Artifact of Doom.
The background material lists several not seen in any armies, such as the Thyrrus, which resemble more pulsating bags of meat and tentacles than anything else, and the Umbra, which are essentially black orbs filled with goo, and are suggested to be simply "parts" of a larger interdimensional creature.
The Hrud, who are apparently evolved from a worm-like creatures, resemble a set of interconnected spines in a vaguely humanoid shape. They can "walk" more or less vertically on two of these spines, use the other two as arms, are relatively pacifistic until disturbed (they usually infest lower levels of the imperial hive cities) and have a very advanced and enlightened religion that worship a deity, parts of which might be the aforementioned Umbra.
The only humanoid aliens from the boardgame/rpg Battlestations are the humans.
The 3.5 Edition supplement "Lords of Madness" describes aliens of forms various and sundry. These include: the Aboleth, hermaphrodite catfish/eel/squid spawn of the Far Realm with Genetic Memory; Illithidae, a genus of creatures related to the iconic mind flayers, a group that includes gigantic, pulsing, psionic brains and the deceptively innocuous mind flayer larvae; Tsochari, a parasitic lifeform from a cold and distant planet who enter and control the bodies and minds of spellcasters for some sinister purpose; the Silthilar, an ancient race of wizard-scientists who have transformed themselves into hive-minded swarms in response to a particularly virulent magical plague; and the Beholderkin, insane levitating spheres with many eyes in disturbing places.
It also includes the "Fleshwarper", a prestige class which allows one to acquire traits from such creatures, eventually undergoing a transformation into a minor Eldritch Abomination.
Other D&D examples include many, if not most, extraplanar creatures. Most elemental entities (with the possible exception of genies) would qualify, as do most Outer Planes denizens.
Most of the Alluria Publications "Remarkable Races" series for 4th Edition are humanly comprehensible and fairly easy to play, but the Squole and Relluk ... sentient oozes who only have personalities because they're imitating the fact that humans do and reproduction-obsessed ancient robots ... yeah.
The Migou from Cthulhu Tech. Semi-fungoid, hyperintelligent insects who don't feel human emotions...except, of course, for the "fear-born genocidal hatred of anything that looks like it could be half as advanced as they are" part. Actually, scratch that. It's an insult to human assholes everywhere.
GURPS: Space spends quite some time on how to design really weird aliens. The starfishiest designs are the various "exotica" such as living nebulae or sentient magnetic fields.
Eclipse Phase features the Factors, sentient creatures that evolved from something resembling slime mold. It also features the Exhumans, humans who have effectively turned themselves into Starfish Aliens through radical modifications. EP specifically advises that if you're creating a new alien race, you should keep them alien, rather than just Rubber-Forehead Aliens. There are enough rubber foreheads among the transhuman population as it is.
Flumphs in the Pathfinder setting are silly-looking intelligent floating jellyfish monsters from the Dark Tapestry (outer space, with Cosmic Horror Story influences). Unlike many Dark Tapestry creatures, flumphs are friendly to terrestrial life.
Brethedans are large, intelligent floating creatures that resemble a cross between a blimp and a jellyfish, native to gas giant worlds. They don't favor technology, but can reshape their physiology to meet the demands of different situations.
The Exalted shard Heaven's Reach has the Kranix, who are described as a hard-shelled octopus.
In classical Exalted, the demons known as agatae are enormous, incredibly beautiful rainbow wasps with inhuman mentalities.
Starfleet Battles features (in addition to all the starfish aliens that could be found in TOS and TAS — but not the movies or later series) the Hydrans as a major race. They are a three-armed, three-legged, three-gendered methane breathers — though they are surprisingly human-like in thought and society despite that (and in Starfleet Command the universal translator outputs their speech with a plummy British accent).
The 2008 European live tour of The Rocky Horror Show- ie, a fully staged live performance, not just the movie and Audience Participation- had this as a twist ending. Riff Raff and Magenta reappear toward the end as twelve-foot-tall monstrosities with human upper bodies mounted on long robes concealing God-only-knew what, thus making their (and Frank's) human appearances throughout the rest of the show nothing more than A Form You Are Comfortable With. This opens up all kinds of new implications about Frank's addiction to human sex, his building a human, the declaration that "[his] lifestyle's too extreme", and Riff and Magenta's eagerness to return to their home planet.
SimEarth: Can literally happen if starfish evolve to be sentient.
Achron has the Grekim. A race with 3 genders that by and large resemble giant cyborg squid. Known to be masters of time travel.
Star Control 2 is absolutely crammed full of these species: the Slylandro (gas giant dwelling bubbles), the Umgah (blobs with various tentacles, mouths and eyes scattered about), the Ur-Quan (Giant tentacled space centipedes), the Talking Pets/Dnyarri (sentient psychic frogs), the Ilwrath (giant spiders), the Chenjesu (silicon-based crystalline lifeforms), the Zoq-Fot-Pik (three allied races who resemble a mutant houseplant, a purple clam, and a blue radiator), the Mycon (fungus), the Supox, the Spathi (one eyed clamlike mollusks)... and most especially those happy *campers* , the Orz (tentacled parrotfish), who, it is hinted, are the *fingers* of an Eldritch Abomination. Most of the aliens are humanoid enough in psychology to communicate with, at least — except the Orz and the Mycon.
Star Control 3 also introduces some new really aliens: the Owa, the K'Tang (underneath their power armour), the Yorn, the Lk, the Precursors and the Eternal Ones's along with bringing back many of the aliens in Star Control 2.
Command & Conquer 3: Tiberium Wars has the Scrin, though it's entirely possible that the none of the Scrin units we see are actually the Scrin themselves, just bio-robots or piloted bio-machines.
Perfect Dark, opposite the benevolent Maians, aka The Greys, has the evil Skedar, which are squid-like Starfish Aliens, although equipped with anthropomorphic Powered Armor.
Waking Mars features the Zoa, and the Sentients, which look like balls of extraterrestrial spaghetti.
Most notable species in Metroid games are Humanoid Aliens, but there are plenty of sea stars. The Ing of Metroid Prime 2 and the X of Metroid Fusion are two sea star species that do influence the plot a great deal.
A more obvious example would be the titular Metroids themselves, being floating jellyfish on the border of Energy Beings. The games give us a few different ways for Metroid to develop into uglier forms too.
Mass Effect has a number of unusual alien species that cover the whole range from slightly strange to completely bizare.
The hanar look something like dog-sized pink jellyfish with seven feet long tentacles, speak through bioluminescence (using Translator Microbes to communicate with other species), and have the tendency to refer to themselves as "This one" (because to the hanar, using one's name in public is egotistical).
The rachni are big, venomous creepy crawlies who at one point in the past were the most powerful alien species in the galaxy. While individual rachni drones appear like mindless beasts, under the telepathic control of a queen they can build faster than light spaceships and threatened to defeat the combined forces of the Citadel Races.
The elcor resemble elephants without trunks that have been crossed with gorillas and stand about two meters tall at the shoulder. As their communication relies heavily on body language and pheromones (both too subtle for other species to decipher), they lack the ability to talk in anything but a flat monotone, which they compensate for by beginning their sentences by stating the emotional state of their statement, even when it is "With barely contained terror: Fine have it your way.". However, except for their body size and unusual speech, they appear perfectly normal when interacting with other species.
On the edge between Starfish Alien and Eldritch Abomination lies the Thorian. Described as a plant, it resembles more a giant growth of fungus that has lived for thousands of years and can use its spores to take telepathic control of other creatures and even produce crude humanoid spawns to defend it. As it can absorb the memories of creatures it consumes, it has seemingly limitless knowledge about the galaxy.
The geth look humanoid in shape, but that is because they were designed to work in homes, factories, military installations, and hospitals made for the humanoid quarians who built them. However, the bodies are actually just mobile server platforms for the actual geth, which are relatively simple computer programs that can move between platforms at will. An average platform houses a few hundred of these runtimes, making every geth a Mind Hive.
And then there are the Reapers, looking like a kilometer-long armored cuttlefish with Glowing Eyes of Doom... even though they borrowed that appearance from the Leviathans, the race that created them. The Leviathans themselves have the same body shape but a more organic and somewhat insectoid appearance with a gray, chitinous-looking shell instead of black, metallic armor. Oh, and the Reapers can Mind Control organic beings while the Leviathans can mind control REAPERS.
It should be noted, however, that the vast majority of Mass Effect species are Starfish Aliens in biological structure only - their psychology, on the other hand, is very compatible with human psychology. The asari, turians, salarians, quarians and batarians are more or less humans in a psychological sense, just with different bodies. Even the krogan and vorcha exhibit many human stereotypes. The only notable exceptions are the rachni, geth, the Thorian, the Reapers, and the Leviathans.
Also note that the only humanoid species that seems to have alien psychology are the drell. They believe that their bodies and souls are completely separate from each other and that sometimes their bodies are not under the control of their free will. This colored their psychology to the point that some of the drell we see can be forgiven for atrocities through that belief (Heel-Face Revolving Door is perfectly understandable, attempted murder can be forgiven under the clause of "battle-sleep," etc).
The Combine Advisors, which look like giant brown-grey larvas the size of a van. The only exterior feature seems to be a small 'face' in the front that is nothing more than a mouth from which they can extend a long tentacle tongue, which they jam into the brains of captured humans, possibly to read their memories. Otherwise, they move and interact with their environment purely by telekinesis.
Vortigaunts are about human size but have one huge red eye and multiple smaller ones, as well as a third arm on their chest. They are also telepathic and in constant contact with any others of their race within at least several dozens of miles, and can produce very powerful blasts of electricity. Indicated by Episode One, they exist in multiple dimensions at the same time and can create interdimensional barriers without the use of any visible technology, and in Episode Two revive a fatally wounded human after several hours without any medical treatment. They also believe in souls, reincarnation, and a kind of afterlife, which based on their telepathic abilities and multi-dimensional nature might even be true.
Half-Life has the Controllers, who have an almost identical body to the Vortigaunts, but can levitate, have giant heads (that flop open to show their brains are crystals), and shot balls of energy from their hands.
Pokémon are (in and out-universe) theorised to be aliens from a distant planet. Some thusly qualify as Starfish Aliens, and some don't:
The most alien would probably be Ghost-types, due to the fact that they're translucent, phaze through walls and can feed on the emotions of others. However, they still breed and lay eggs like all other Pokemon.
In a literal example, Staryu and Starmie are hinted to have come from outer space. They flash their crystals to the night sky, emitting strange radio waves. They also have No Biological Sex, despite being fully organic and non-legendary.
Deoxys, who is not only explicitly stated to be an alien, but who lacks a mouth, nose, has tentacles, shapeshifts, and is shown in the movie it stars in to communicate via pulses of light from a crystal which acts as its brain.
Heading back to the generation that brought you Deoxys is a pair of peculiar alien Pokémon, Solrock and Lunatone. Given their appearance and typing they can be considered living hunks of stone shaped like, respectively, the Earth sun and the Earth's moon. They levitate in the air, and if the supposedly reliable Pokédex is to be believed, Solrock radiates intense light, gives off heat, absorbs power from the sun, and reads the emotions of those around it... meanwhile, Lunatone's red eyes paralyze foes with fear, its power "ebbs and flows with the lunar cycle", and brims with power under the light of the full moon.
The Zerg from Starcraft have completely monstrous forms (until they start assimilating humans), a hivemind-based society and "hive clusters" made of "buildings" that are actually huge, sedentary living Zerg creatures. They reproduce by larvae that are born from one such living building.
The buildings are technically more like organs than creatures, given their specialized functions and dependence on the Creep (an undifferentiated mass of flesh/hide/circulatory system which covers Zerg-infested terrain) to exist. How cute.
The zerg-protoss Hybrids (hinted at in Brood Wars and shown outright in some parts of Wings Of Liberty) qualify: gigantic blue or purple aliens with tentacles and spikes. Some of them float. All of them have defenses equivalent to most buildings. They also may or may not be similar to the Xel'naga Precursors.
The alien from the original game (also appearing in the expansion) that just happens to be the entire planet. Well, most of the plant and animal matter on the planet anyway.
The aliens from Crysis are fluke-like beings with translucent bodies who live in zero gravity, and probably couldn't survive outside of their ship on their own. Their Mecha-Mooks and Powered Armor are also distinctly inhuman, resembling the robotic squids from The Matrix films rather than the standard bipedal robots.
In Crysis 2 they are aptly named Cephalopods (or Ceph for short). They now use agile bipedal robots, piloted by a tentacled organic mass on their backs (which may or may not be an actual alien).
One of the crewmembers in Unreal II: The Awakening was an alien whose body was some sort of liquid or energy, and who interacted with everyone using a suit of humanoid-shaped Powered Armor with a large transparent dome in the chest where his "face" was. With only a tenuous understanding of human culture, he was also the Funny Foreigner.
Later you visit a living planet, a planet covered by one giant organism.
The S'pht from the Marathon games usually fly around in powered armor, but appear to resemble brains with an eye and arms◊. This is because they are all cyborgs from birth, with both the biological and mechanical halves reproducing at once, making them Mechanical Lifeforms to one degree or another. Some information in the games indicates that the S'Pht wouldn't be sentient without their cybernetic parts, which were first grafted on by the Jjaro.
While most of the aliens in Shadow the Hedgehog appear to be vertebrates, Doom's Eye is a floating purple starfish with one eye. Basically. The Black Arms' spawn are also tiny slug babies, and Black Bull looks more like a one-eyed grub meets Clefairy from Pokemon. There are also massive hints that the aliens are Bee People with a Hive Mind, especially when Black Doom tries and fails to control Shadow with his mind.
Several of the Twilight Cage aliens from Sonic Chronicles: The Dark Brotherhood also count. You've got the Voxai, a race of manta-like psychic beings, who form a Hive Mind if their leader is oppressive with his psychic suggestions of purpose; and the N'rrgal, a Hive Mind race of slime beings led by a queen, who manifests when enough drones merge together. The Zoah and the Kron are more humanlike, though the Zoah are all giants in what appears to be Powered Armor, and the Kron are made of rocks.
The vast majority of the Covenant species in Halo are to one degree or another humanoid in structure, excepting the Hunters/Mgalekgolo. Though outwardly they look like humanoids, in reality each Hunter is a collection of hundreds of eel-like organisms (the Lekgolo) gathered together into an individual Hive Mind that operates as a single sapient being, formed into a humanoid shape by their battle armor.
The Drones/Yanme'e, insects that have a hive mentality and strange eyesight.
The Flood and The Gravemind. Pure Forms especially, as they seem to have their own uniquely engineered anatomy, and can change from a spider-like "Stalker" to either the lumbering bear-bug "Tank", or the really odd, bulbous, porcupine-like "Ranged" form.
It gets even crazier in The Forerunner Saga, which shows that Flood biomass could take all sorts of crazy forms. Additionally, the Flood themselves are revealed to be the most recent form of a previous species of Starfish Aliens, the Precursors, who were basically god-like beings that could assume any form they wanted to (both physical and immaterial) and were responsible for seeding life on many galaxies. They're also apparently older than the universe itself.
The Engineers/Huragok, who resemble large pink tentacled slugs that float above the ground using two gas-bags. Their tentacles have the ability to split into millions of thread-like cilia, which they use to fix or build just about anything. The Engineer equivalant of sex is a couple (sometimes even a trio) working together to actually build their child. Their psychology is a little strange too. They don't seem to care if they're helping the humans or the Covenant, so long as they have something to fix. Indeed, they weren't even produced by natural selection, originating as basically biological robots built by the Forerunners.
In City of Heroes, the playable "Kheldian" aliens are formless energy creatures who can extend their lives by symbiotically combining with other intelligent lifeforms, who gain energy powers and the ability to transform physically into any of the Kheldian's previous hosts. The two alternate forms in game are the "Nova" (a floating tentacled creature) and the "Dwarf" (a huge armor-plated biped). Their EvilCounterparts are the Nictus, who are basically vampire Kheldians. Apparantly, turning evil gives the Kheldians powers based around dark energy, which do not disapear if they redeem themselves.
Freespace has the Shivans, which can best be described as gigantic five-legged spiders. Their bizarre shape is apparently due to them having evolved in zero-g: they are incredibly agile and acrobatic in such an environment. The list of strange attributes about them is too long to list here, but it's been stated that they can survive prolonged exposure to vacuum (one cutscene dropped from the game had them jumping out of their ships onto a space station to board it... without any kind of suit). Furthermore, their means of communication is, for most of the games, completely unknown to the Terrans: and since Shivans seem to exist only to blow up things that are not Shivan, they were named for Shiva, the Hindu god of destruction.
Escape Velocity Nova has the Wraith, a race of living ships with an innate cloaking ability, and the Krypt, a mysterious Hive Mind which considers itself to be the only form of life in the universe.
While in Master of Orion 2 was primarily populated by Rubber-Forehead Aliens, Master Of Orion 3 seemed to want to embrace this trope by cutting out most of the old aliens and reimagining the ones they kept. The reptilian and insectoid species became less humanoid in general, the previously "humanoid rock" Silicoids became intelligent crystal fractals, they added a new category of gas giant dwellers that seem to resemble jellyfish, etc. Also along these lines, they changed the terraforming system from "creating a more perfect world" to the more realistic "adjusting the world to suit the inhabitants." Which has the annoying (but presumably realistic or at least internally logical) side effect that conqering one species' "Gaia" is likely to give you a useless hellhole.
Numerous X-COM alien varieties fit this description. From UFO Defense come the Celatids and Silacoids-a floating kidney bean and a silicon lifeform, respectively; from Terror From The Deep hail the Lobstermen, Calcinites (blobs of protoplasm inside diving suits), and Tenatculats (aquatic brains with tentacles and a single eye), and all the aliens from Apocalypse.
Arguably the Chrysalids in XCOM: Enemy Unknown can be this, with them no longer being humanoid biomechanical aliens, like in the first X-COM and instead being something of a cross between a spider and a crustacean. They still have a vaguely humanoid torso though so YMMV.
Enemy Unknown has probably one of the weirdest aliens of the series, the Outsider. They only show up when an alien ship is shot down, and appear first as hovering crystals that suddenly create humanoid forms, complete with plasma rifle. What they are is anybody's guess, as Doctor Vahlen describes them as "almost made of pure energy" and hypothesizes that their function amongst the alien armies is as a communication device. At the final mission, when the Uber Ethereal is explaining the various origins and functions of the alien races, it does not talk about the Outsiders at all.
The Cover Based Shooter spinoff The Bureau: XCOM Declassified also plays this fairly straight, with the aliens being weird, symbiote-esque blobs who travel via giant, floating black cubes in the sky.
While most alien species in Anachronox are Rubber Forehead Aliens, the Time Minders are large, white, insectile aliens who perceive time non-linearly. Naturally, they function as the game's save points.
The Cocytans from the 1995 adventure game The Dig, which look like the 9 feet offspring of a rooster and a llama.
The TYPES in Tsukihime, which are actually something like the manifested power and will of the planets themselves. The most well known one (besides TYPE-Moon, Crimson Moon Brunestud and Arcueid's father) is TYPE-Mercury, by far the most powerful Dead Apostle. It's so bizarrely alien that it lacks a concept of death. This doesn't make it unkillable, merely that as its concept of death is completely alien to the way life on Earth dies, Shiki can't kill it... despite being able to kill parts of the Earth (or possibly the whole thing at once if he knew where to stab) and inanimate objects.
Meteos is flooded with these. Majority of the playable planets are chock-full of aliens that are anything but humanoid, from the jellyfish-like Oleanans to the gas-composed inhabitants of Brabbit/Aetheria to the insectoid race of Gigagush/Vortina to the snake-shaped Arodians.
World of Warcraft has some pretty weird creatures on Outland, such as marsh striders. The Scourge faction has some very weird flying spider-bat combination things that screech unnervingly and never fail to give you the creeps. The naaru could also count, though they are energy beings, they lack faces and bodies and limbs as we know them.
The Many from System Shock 2 is/are another extremely disturbing example. It/they is some sort of hive mind which consists of many separately-moving creatures (including humans who are mind-controlled by worms that latch onto their bodies) but also of at least one gigantic, living and presumably sentient mass of living matter.
The Einst from the Super Robot Wars series are a hive mind of creatures that seem to be able to take any form, though they stick to a few specific ones such as skeletal monsters, vines wearing robes, or empty suits of armor. They exist in an alternate universe, only occasionally coming to a world occupied by humans, and most of them can only communicate telepathically to specific people who have a connection with them. (And still... Talk... Like this...) They are, or at least believe themselves to be, the eternal guardians of the multiverse that existed since the dawn of time, and have no personal issue with humanity except that our free will and hotblooded}}ness is slowly eroding away the foundations of the universe.
Owing to the amazing procedural generation of Spore, a good deal of the species you create or encounter can be this. The most famous Spore creature, the Willosaur, is a tripodal reptile/dinosaur-thing with three eyes and a prehensile tail. And that's one of the more normal creatures you'll find.
The Lumas in the Mario series. They aren't exactly as bizzare as others on the list, but they're body shape is literally that of a star. They can be found anywhere and consume peculiar objects called Star Bits.
The Centaurans in Otherspace resemble floating crystalline jellyfish, with radial symmetry, over twenty eyes, telepathic communication, tentacles for manipulation, and a mechanical device to convert air into something breathable. Oh, and they consume any of their race who shows any hint of psychotic thoughts.
''UFO: Aftershock'' has the Starghosts, strange aliens that appear later in the game. The Starghosts use "pet" creatures that range from animated shuriken to giant spiders. However, aside from psionic projections, the true form of the Starghosts is never seen.
The Boron of the X-Universe look like Rubber-Forehead Aliens over comms, but you only see them from the neck up. They actually look like this◊. They're an aquatic species that evolved on an ocean world with an ammonia atmosphere, and have three genders. Meanwhile the Kha'ak are so alien that the Commonwealth races are physically incapable of communicating with them. They're Bee People that have characteristics of both birds and insects, are roughly 75 centimeters in size, and communicate by gestures and pheromones.
The BETA from the Muv-Luv series are made up of a collection of non-sentient drones, controlled by one sentient being per population. The sentient being communicates with the other units telepathically, instructing them to construct hives and, if necessary, to fight strategically. None of the various strains of BETA drones have any apparent physiological relation to each other and the sentient being, itself, resembles a pod with six eyelike constructs and several tentacles. They are unable to recognize carbon-based life-forms, such as humans, as sentient organisms, as silicon is viewed by them as a primary component of all life.
The Necromorphs from Dead Space. Some look like they're human, right up until they try to eat your face, while others are vaguely human if you take away the vestigial limbs and built-in swords, while still others are nothing more than a nest of Combat Tentacles growing out of a ball of meat.
Dead Space 3 has an interesting take on this. Tau Volantis had alien life that was decidedly dissimilar from human life. It was so different that when scientists discovered what appeared to be frozen corpses of these aliens, they were greatly surprised when they came back to life once thawed. They tried to communicate, but the aliens attacked instead. The reason being that they were actually Necromorph'd alien corpses, not the actual alien species, which was long extinct. The humans couldn't tell the difference.
Shockwave has the Bruntshen; four-legged with big bugged-out eyes, giant teeth and antennae on their heads. They nonetheless evolved on a remarkably Earth-like planet.
It's first hinted, and later stated outright, that under his Mobile-Suit Human(oid) exterior, Sam Starfall of Freefall is not remotely humanoid in form. Word of God states that without his suit Sam vaguely resembles a boneless stick-man made of tentacles. Once his "arm" was shown without suit; it was a bunch of tentacles strapped together to vaguely resemble a human arm.
While the Walkyverse's native Purple Aliens and permanently imported Melotians and Zinoboppians are classic diminutive humanoids (even though the Aliens are quite monstruous under their armor), the Martians are enormous tentacled monstrosities best described as a cross between a mantis and an octopus.
Unicorn Jelly starts as a basic Final Fantasy-like world, with Jellies and Slimes, Orcs, Witches, etc. Eventually it is described as "putting the same level of detail than Tolkien's works, but to astrophysics instead of society". For example:
The universe itself. It has no atoms, but a set number of "tratons", that are "polihedral forms made of dimensional energy", as opposed to our spheres of mass surrounded by energy. The tratons cannot be transformed into one another, and there is a set number of each, from the start to the end of the times. When the humans arrived, in an event that may or may not have destroyed our universe, their matter was "translated" into the closest possible alternative, but since it wasn't exactly equal, they need constant doses of a plant/animal, quite strange on itself, called Vlax (it's by the bottom). Also, the gravity equivalent pulls from space, rather than from matter, so there's an absolute up and down (walk to the other side of the world and you fall into space, etc). An object sufficiently large stops being affected by it, so they have "worldplates", that are large, plain, triangular worlds, arranged in triangular patterns that make them look like a recursive Triforce, but it gets weird when you look at the 3-D model. It also has the "finite yet unbound" thing our universe has (we think), that if you walk too far in one direction you end up coming back home from the other side. Including falling so far down that you pop up from above. And therefore, when the humans destroyed one of the worlds, the pieces stopped being immune to gravity, fell, and destroyed further worlds, creating an ever-growing pillar of debris that is eventually going to engulf the entire universe. Of course, it will eventually settle and reform in the triangular worldplates again, as shown by an aeons-old relic from an obviously non-human nor local civilization.
Next, as per their adaptation to the above, the Humans themselves are starfish aliens. When the smartest girl ever born there finds some ancient astronomical charts from our world, she finds out that they had come from a universe "dominated by the geometry of the sphere", and deduces that "The society must have been terribly hierarchical, with the rich and powerful dominating the top of the world-domes, and the poor dammed to live in the slippery end, where the lose of life to the curvature of the world must have been a constant dread. This world must have been like a paradise to them, with endless extensions of safe, plain land."
And lastly, a bit on the locals. The Crystal Dodo and the Dodofruit Domes. Each worldplate has exactly 303 Crystal Dodos, each living in a patch with 303 Dodofruit Domes each. Unless humans arrive and kill some of course. Both are immortal, incapable of reproduction, and the Dodo goes around its patch, eating only the topmost fruit of each one and leaving. By the time it goes back, the fruit has grown back. Sounds nice? The Dodo is a mindless pair of legs with a mouth between them. It moves the exact number of steps between each Dome, eats the fruit, and starts walking again, forever. No two Dodos overlap each other's path, and all the native creatures instinctively avoid these areas, even the sentient Jellys, though the Dodo has no mind, no sensorial organs at all, and no possible means of defending itself. It's a fruit eating automathon. As of the Domes, they are highly intelligent and sentient beings, though incapable of reacting to its various and delicate sensorial inputs. And the fruits are actually highly sensitive eyes.
Other native creatures are quite strange. For example, the crystal basilisks don't have musculature, they walk by growing new legs in front, moving them down their bodies, and then breaking them off at the back. As awkward as it sounds, they're a fast, dangerous apex predator, and very dangerous to humans. They reproduce by injecting their prey with self-assembling crystals, which eat them from the inside out.
Schlock Mercenary has a fair few, although also plenty of Rubber-Forehead Aliens and everything in between. The titular Schlock is perhaps the best example, being an 'amorph' that is frequent described as looking like (and being mistaken for) a pile of crap.
Aliens in Buck Godot: Zap Gun for Hire range from fairly humanoid to extradimensional beings who can't even be percieved by, let alone communicate with, humans. A special place is reserved for the Uligb, who exist in 13˝ dimensions and love popsicles. Which they stuff and mount. They also look a little like the bastard son of a jellyfish and a Klein bottle, with clusters of eyes added to the mix. Another particularly weird one is the Teleporter, who more or less looks like a whole bunch of free-floating hexagonal windows, with pale hands coming out of almost all of them, and a dopey, buggy-eyed head coming out of the last one, and believes a species hasn't achieved true intelligence until it can teleport whole planets around.
Except for a one-strip crossover with Zeera the Space Pirate, all of the aliens in The Inexplicable Adventures of Bob! have been shown to be nonhumanoid, at least in their true forms. These include the Ipecacians, who resemble lobsters; the Fleenians, who are rubber-limbed centaurs with giant eyeballs for heads; and Ahem, who resembles a three-legged jellyfish. The butterfly-like Nemesites such as Princess Voluptua and Fructose Riboflavin frequently use shapeshifting technology to appear human, however.
Aylee (short for "alien", natch) from Sluggy Freelance started as an obvious Alien homage, but periodically mutates in an ongoing attempt to adapt to the alien (for her) terrestrial environment. Each form is radically different, and some are dramatically non-human.
The Action Hero's Handbook: the chapter on communicating with extra terrestrials assumes that any aliens you're lucky (or unlucky) enough to encounter would be these, but holds out the hope that they would still be able to recognize concepts like numbers and shapes. (The book reasons that any life form capable of the level of technology necessary for interstellar travel would at least have the alien equivalent of astrophysics.)
In Spacetrawler, most of the aliens are humanoid or based off some Earth animal, but there are a few more unusual specimens: Krep is a quadruped and has six tentacles on his face for manipulating objects. Luunock resembles a cross between a caterpillar and a venus fly trap. And a bartender who shows up for only one page has arms growing out of his mouth.
The story Three Worlds Collide features two alien species designed to be radically different from humans. One of them is sentient silicon-based, and has evolved a reproductive mechanism involving spawning billions of extra young and eating most of them (whilst semi-sentient) - as such their concept of 'good' literally translated as 'eating babies'. The second are powerfully hedonistic tentacles for whom pretty much everything evolutionarily advantageous is extremely pleasurable. They introduce themselves with a video they created featuring themselves in a childbirth-related porn film, repeatedly putting a baby back in to a woman; The story deals with the ethics of interaction with these two alien species.
Snaiad is an ongoing xenobiology project by Nemo Ramjet which covers the biosphere of a fictional extrasolar planet as catalogued by human colonists. A short list of the differences between Snaiadi and Terran vertebrates: Their skeletons are carbon-based rather than calcium based (making fossils rather hard to find, and bones an excellent source of fuel); a portion of their musculature structures are hydraulic instead of contractile, i.e. they push instead of pull; they have two heads, one for eating and one for reproduction; and a number of aquatic species move by way of biological jet engines, a quality they share with Earth octopuses, though still unique as far as vertebrates go. Front legs are optional.
Alpha Centaurians in The Pentagon War are shaped like a cross between xorns from Dungeons & Dragons and R2-D2 from Star Wars. They have muscle-powered wheels in their feet, a 360 degree eye stalk, and four mouths spaced evenly below and between their four shoulders.
The SCP Foundation has an alien CD; based on data retrieved from it, the designers are fundamentally different to humans (for example, taste is their primary sense, and electromagnetism is lethal to them). Also, we are starfish aliens to them.
There's also SCP-163, which is cylindrical, has 8 legs, 4 pairs of arms with different functions and a single compound eye with 360 degree field of vision that sees mainly in ultraviolet. It's also one of the more harmless SCPs and clearly homesick.
And now there is SCP-1701, a race of sentient naturally-occurring nuclear reactors with a mathematic language whose society primarily consisted of philosophical debates. Somewhat subverted as said reactors evolved and went extinct here on earth many millenia ago.
S T R A N G E R S is a sort of catalog of starfish critters: the eponymous strangers have no bones, brains or other internal organs, yet behave like living things. When dissected, they're revealed to be either hollow or stuffed with random objects and substances, such as calligraphy ink and various trash. The information page openly states that no one understands exactly how these creatures work or why they exist in the first place.
The Transformers did this a lot, especially in season three when the focus moved away from Earth. There are the five-faced tentacled Quintessons, the energy-based Tornedron, the living planet of Torkulon and its motley inmates, and in the sequel series Beast Wars we got the extradimensional Vok.
The Quintessons deserve further elaboration. They have five faces, but no actual 'head', just a cylindrical body. They have no arms or legs, and instead get around via floating on an energy beam. If they do need to carry something, they use the tentacles that hang around near the bottom of their body. In their initial appearance, in Transformers: The Movie, they drag anyone they find into a courtroom setting and invariably feed them to their 'pets', the Sharkticons, but they never explain why they're putting up with these trials. Later appearances explain it that they're just jerks, who gladly ruin whole civilisations For the Evulz.
The Transformers themselves are perhaps the limit of how humanoid mainstream aliens can be- Mechanical Lifeforms about ten times our size who can reconfigure their bodies at will to mimic machinery. Most of them happen to have two arms, two legs, and a head, but they sure as heck don't look human.
And "most" doesn't mean "all." Sky Lynx is a space shuttle that turns into a bird and cat, both bodies being equally 'him' whether working together or in two entirely different places. Don't tell him how cool that is; he's well aware of his unparalleled greatness.
G1 Reflector was three largely identical beings in one alt mode (a camera). It's unclear how separate their personalities are. Often referred to in singular pronouns on the wiki.
The Men In Black cartoon series kept up the traditions of the film.
Futurama has fun with this trope. Civilized gut-worms, anyone?
Dr. Zoidberg may look humanoid now, but while going through his developmental stages he resembled various deep-sea creatures. Likewise, humanoid Kif Kroker started life as a tadpole and will eventually age into a swarm of flying hookworms. And both species reproduce rather differently than humans.
The balls from "War is the H-Word".
The anime segment of the Reincarnation episode had a race of mouthless aliens that could only communicate with body language.
The animated miniseries Red Planet, a reworking of the Robert A. Heinlein novel, had "bouncers", sentients the size of soccer balls, and the "locals" of New Aries. They are actually the same race. The bouncers are the juveniles and the locals are the adults.
Though packed with humanoids, Justice League and Justice League Unlimited also showed a few non-humanoid aliens, mainly as background characters.
The snail-like Lacterns. In a stange inversion of live-action, the Filmation's animators found starfish aliens (especially those with no pesky arms or legs) to be much easier and less tribble to animate than human beings.
And several minor ones, like the pillbug-like Em/3/Green, known as a Nasat in the Expanded Universe.
While plenty of aliens in Invader Zim are humanoid, including the title character, there are also plenty that fit this trope, ranging from Energy Beings that resemble amoeba to a floating purple cone with a face.
In mental terms, this article reflects upon the profoundly alien possibilities extrapolated from our own minds, while breaking down each factor that could possibly make alien minds different from human minds.
Scientist speculate that life may exist on Jupiter's moon Europa where there may be a sea under the ice. If they do, they'll probably live very deep down, surviving off geothermal energy. Thus, they would possibly look similar to Earth's own deep sea creatures.
Its also worth noting that deep sea life evolves in one of the most extreme environments on Earth, with very little sunlight, nearly no photosynthesis and extremes in pressure and cold. This radical difference from any other environment on Earth creates very alien forms of life that simply cannot exist elsewhere. Its very little wonder, then, that a number of speculations on life on other planets tend to take inspiration from deep sea life.
Scientists constantly discuss the limits of where life could develop, but the reality is that those limits only apply to the kind of life we're used to. Technically, as long as there is enough chemical diversity, there is the potential for what could be defined as life, regardless of temperature, specific chemical environment, or gravity. This could mean some really bizarre lifeforms are waiting out there.
On our own planet, only the smartest of animals can count for starfish alien status: whales, elephants, chimps, gorillas, dolphins for sure, octopi maybe. Ants, bees and wasps might qualify if we stretch the "sentient" requirement.