While such things as spike-shelled turtles do exist — like the black-knobbed map turtle or the alligator snapping turtle — their spikes are more like blunt knobs and are certainly not capable of seriously injuring anybody. In fiction, spikes on a turtle shell can be used as a weapon that can seriously injure somebody.
If the spikes are custom added to our anthropomorphic turtle, then expect them to have either been glued on or being a custom-made Removable Shell. If the spikes are natural, then the turtle is most certainly a made-up species, being either a mutant or an alien.
As mentioned above, turtles are the most common animals to be given this trait in fiction, but other shelled animals have also been portrayed this way, such as snails, crabs (especially those of the giant enemy variety), beetles, and armadillos. It's a bit more plausible with snails, some of which really do have impressive and sharp spikes on their shells.
A common trait of The Spiny if their spikiness is related to their shell.
- Anguirus from the Godzilla franchise is an Ankylosaurus-like giant monster with a carapace covered in spikes which grant him protection from his enemies and which he can use to attack his enemies by jumping backwards at them to hit them with the full force of his spines.
- The Ankylosaurus in Jurassic Park III and Jurassic World are depicted with armor resembling bony shells adorning spikes, even though the real animal wasn't particularly spiky and had flattened osteoderms embedded into thick skin.
- Tokka from Teenage Mutant Ninja Turtles II: The Secret of the Ooze is a mutant alligator snapping turtle who gains prominent spikes on his back when he is mutated.
- Harry Potter: Streelers are some kind of snails with spikes on their shells that are poisonous. They are first introduced in the video games, where they appear as giant orange snails.
- The Masked Singer: Season 3's 2nd place contestant was the Turtle, who sports a shell adorned with large silver spikes. Downplayed as it's a singing competition, and the spikes are for aesthetics rather than combat: the Turtle goes for a punk-rocker theme, dressed in all black leather with silver studs and the spikes on his head shaped like a mohawk. Unmasked in the finale and revealed to be Jesse McCartney.
- "Steel Shell" is an equip-spell card that takes the form of a turtle's carapace covered in large spikes. It can only be equipped to WATER-attribute monsters and while it increases attack points by 400, it decreases defense points by 200.
- "Monsturtle" is a WATER-Attribute, Aqua-type monster portrayed as a giant turtle with sharp teeth and spikes on its shell.
- There exists a Spiked Black-Red Shell Backpack made by the manufacturing company Bioworld.
- Crash Bandicoot 2: Cortex Strikes Back: In the first few beach levels, one of the earliest enemies Crash can encounter are turtles with spikes on the sides of their shells, which prevent Crash from knocking them aside with his usual Spin Attack, the only way to defeat them being jumping over their sides and knocking them backwards with a Goomba Stomp.
- Dillon's Rolling Western: The armadillo protagonist, Dillon, can attach metal spikes to his shell that enable him to follow up his Rolling Attack with a grinding attack.
- Final Fantasy: The Adamatoise type enemies have sharp spikes on their turtle shells. Later, more animated versions will even tuck themselves inside their shells and attack by spinning at the heroes.
- Kameo: Elements of Power: Major Ruin, an armadillo-like creature who can roll into a stone ball, can be upgraded to have spikes on his shell.
- Jazz Jackrabbit:
- The boss Schwartzenguard is a tortoise with a spiky shell. However, his signature weapon is a spiky flail.
- The boss Uterus is a crab-like clam with spikes on his shell. The spikes are mostly visual since every part of him hurts the player.
- League of Legends: Rammus is a strange mix of armadillo and turtle-like features, part of which includes a thick shell covered in spikes. He can damage enemies by letting them strike him, causing them to stab themselves on his spikes.
- Mega Man X6: One of Rainy Turtloid's main attacks is to retract into his shell and deploy spikes out of the sides before rolling across the screen.
- Omastar is a Pokémon based on an ammonite, an extinct type of mollusk. The top side of its shell has a line of spikes running down the middle.
- Turtonator is a turtle-like Pokémon with a shell sporting black spikes that resemble rock shards. Its Secret Art Shell Trap has the spikes explode if the opponent makes contact with it.
- Cloyster is a Pokémon based on oysters with a spiked shell whose spikes can be shot off when it uses its Spike Cannon attack.
- Super Mario Bros.:
- Bowser is a giant, dragon-like turtle with massive spikes on his shell. While they're mostly to indicate that he's the Big Bad, he also uses them as a Natural Weapon. In the Mario Kart series, his shell is even used as an accessible weapon that can crash through other racers and obstacles. Bowser Jr. and the Koopalings have similarly spiked shells as part of their resemblance to him, as does the recurring Mini-Boss Boom-Boom in Super Mario Bros. 3.
- Mario Kart: The Spiny Shell series is a rather infamous weapon in the franchise for being a Game-Breaker; a blue Koopa shell covered in spikes (sometimes with wings) that is inescapable, unblock-able, and is designed to target whatever character is in first place.
- Spinies are quadrupedal shelled enemies with backs covered in spines, which will harm Mario if he tries to jump on them. Spike Tops, a variant of Buzzy Beetles first appearing in Super Mario World, have a single spike on their shells for a similar effect, which combined to Buzzy Beetles being Immune to Fire — the main way to deal with regular Spinies — makes them a bit of a problem to deal with.
- Mario & Luigi: Bowser's Inside Story: Midbus, being an Evil(er) Counterpart to Bowser himself, has a spiked yellow shell. He's not a turtle, though, more like a cross between a boar and an armadillo, and his spikes are curved instead of straight.
- Warcraft III:
- Turtles have the Spiked Shell ability, which causes melee attacks to deal damage to the attackers.
- The Crypt Lord (undead mantis-beetle-spider... thing) hero has the similar Spiked Carapace, which deals damage to melee attackers and increases the Crypt Lord's armor.
- The Horde's Spiked Barricades upgrade deals back fixed or percent-based damage (depending on the patch) to enemy attackers.
- SpongeBob SquarePants: In "Ugh", a giant prehistoric ancestor of Gary is depicted as having spikes on his shell, giving him a more dinosaur-like appearance.
- Tokka from Teenage Mutant Ninja Turtles (2012) is an alien turtle creature as big as a mountain with large prominent spikes on her shell.
- A more realistic example with Raphael in Rise of the Teenage Mutant Ninja Turtles, here an alligator snapping turtle with the spikes to match.
- Many species of dinosaurs in the suborder Ankylosauria actually did possess large spikes on their armored shells. While many of them were blunt, some species had sharp spikes arranged along the bottom of their shells that were obviously useful as weapons. Edmontonia, a species of nodosaur, had sharp, forward-facing spike protruding from its shoulders that it is believed to have used to ram predators with, inflicting serious wounds.