Take a look at an urchin. Those little critters are balls of spines that seem to do nothing but stay in place, just waiting to be stepped on and deal the hurt to anyone touching them. For extra injuries, urchin spines are actually quite brittle and tend to break when stepped on, remaining embedded in the swimmer's skin. And some of them are even poisonous! In other words, they are the living embodiment of the Spikes of Doom — painful, dangerous and, well, spiky.
As such, when an accident-prone character takes a vacation to the beach, expect them to inadvertantly walk on one, cue the Agony of the Feet.
They are also quite common as underwater obstacles in Under the Sea settings, usually as immobile versions of the Painful Pointy Pufferfish. Standing motionless on the walls, they are quite effective at complicating the navigation during a level, made worse by the fact that their spikes shield them from most of the dangers, making them quite the dangerous creature.
In visual media such as cartoons or video games, it's not uncommon for sea urchins to be visually simplified into near-perfect spheres with faces and a studding of large, conical spikes, going from being regular if spiky animals to more or less living caltrops.
- In Monsters University, the first round of the Scare Games consists of a simulated run through a child's bedroom, with urchins in place of the (supposedly) toxic items the monsters would have to avoid. Touching one causes violent swelling.
- In Surf's Up Cody accidentally steps on a sea urchin after his big wipeout, which leads to the "urinate on it" remedy. As a bonus, there is also an interview clip of the sea urchin disputing that he was merely stepped on.
Sea Urchin: Stepped on me? Stepped on me? Are you kidding? This guy was dancing on me! I mean, just look at this. [Points at spikes] Broken, broken, gone, gone, broken, broken, broken...
- In Thunderball, Domino steps at some point on an urchin spine poisonous and painful at the same time. Taking her ashore, Bond bites the spine out.
- In Blood Fever, Jana Carnifex, Ugo's sister, attempts to kill Bond and Amy while they are Skinny Dipping. Bond tricks her, however, by jumping off the rock, while Victor distracts her. She slips and falls into a bed of sea urchins, where she finally dies from the pain and poison. As Bond and Amy wade to the surface, Amy suddenly steps on a sea urchin. Bond knows exactly how to remove it.
- One Geronimo Stilton book has the titular character getting pricked by a sea urchin left on a hotel bed by his nephew Benjamin, who intended to show it to him.
- In an episode of Crazy Ex-Girlfriend, a creepy security guard blackmails Paula into going to an aquarium with him to see the touching pond. There, he demands that she put her hand on a sea urchin, facing him as she does so he can see her reaction. It's framed as though he'll be getting a sexual thrill out of seeing her in pain, but after she awkwardly describes the sensation as 'spiky', he cheers and then excitedly runs off to see the next exhibit, showing he actually just wanted to share the experience.
- A recurring enemy in Adventure Island series is an urchin that floats back and forth in underwater levels.
- Donkey Kong:
- Donkey Kong Country 3: Dixie Kong's Double Trouble! introduces the Lurchin enemies, sea urchins that can open up to reveal the creature's grotesque, angry face. They, of course, are harmful on contact and can only be defeated by Enguarde (only when their shells are open) or the Nibbla (which can eat them but will be pretty pissed off about it). Their leader Barbos also appears as a boss.
- Giant purple Sea Urchins appear as obstacles in several underwater levels in Donkey Kong Country: Tropical Freeze, both as immobile threats and floating around in a set movement pattern. Only Cranky Kong's cane stands a chance against them.
- Averted in the Freddi Fish series, where sea urchins are used as currency in the undersea world and none of the characters are ever shown getting hurt by their spines (Gill Barker even bites on them in the same manner as biting on gold).
- Gordos, some of the regular Kirby baddies, give very strong vibes of this trope. The completely invincible enemies are urchin-like monsters (though their spikes are arranged on a perfectly circular pattern leaving their faces and their backs smooth) which can be found not only in water but on land as well.
- The Legend of Zelda: Link's Awakening uses sea urchins to block paths in Toronbo Shores. While they deal damage to Link on mere contact, they can easily be defeated with a sword.
- In Octogeddon, Ursula the Urchin is an animal buddy which can fire a flurry of spikes all around her, damaging every enemy they strike.
- Fallen London:
- Sunless Sea:
- Aigul is an undersea port built in a giant Lorn-Fluke (read: city-sized alien urchin). Everything within it is pierced with its spines, and navigating within it is rather hazardous if the flavour text is anything to go by.
- Smaller Lorn-Flukes (still twice the size of your ship, mind you) appear as enemies around the Zee and try to ram you with their spines. That isn't even the scariest thing they can do: they're are able to wield Correspondence, which acts like some kind of Brown Note and will heavily damage your ship.
- Unfortunately for the Sunless Sea veterans, the Flukes didn't stay in the Unterzee: in Sunless Skies, the ones that moved to the High Wilderness are called Scorn-Flukes, and if anything are even worse than in the previous game, charging your locomotive in the middle of open space with all their urchin-like bulk and speaking Correspondence even more fluently. There's also whatever sort of eldritch Fluke that you can find in the mists near Worlebury-juxta-Mare; it can't hurt you, but it's so big and horrible-looking your terror will skyrocket in its presence.
- Sunless Sea:
- Super Mario World introduced the purple Urchins to the Super Mario bestiary. Do not let their goofy appearance fool you, their spikes do hurt. In their Super Mario Galaxy appearance, they are mobile and can even extend their spikes a little if Mario gets too close from them.
- Super Smash Bros. Brawl introduced the Unira (the sea urchin baddies from Cluclu Land) as items. When thrown, they will fix themselves at their landing spot and extend their spines. Any foe coming in contact with these will be damaged and dealt knockback.
- In the Wii Play: Motion minigame Treasure Twirl, many urchins are attached to the walls to hamper the mobility of the Miis. Like any other enemy, tounching them will deplete your Oxygen Meter and make you drop a treasure chest if you carrying at least one.
- Urchin enemies in Xenoblade Chronicles 2 are usually territorial and will agro if you get too close. Their spikes double as a layer of armor that block most physical attacks. With few exceptions, you must wait for the urchin to initiate an opening to strike its core in order to Topple it and engage in higher combat functions.
- SpongeBob SquarePants:
- In "Nature Pants", after SpongeBob gets zapped by jellyfish, he tries to call it a night by resting in a cave, all while bearing the cold with only a kelp blanket to barely cover him. All of a sudden, he gets a painfully itchy feeling, and it turns out that he's covered by poison sea urchins.
- In "Eek, An Urchin!", urchins get inside the Krusty Krab, which are treated as a major infestation.
- The Ancient Greek writer Demetrius of Scepsis recounted a Spartan being invited to a banquet where seafood was served, and ate an urchin whole by putting it in his mouth and biting down (without looking at how other, less Proud Warrior Race-types were eating them). He then said that he wasn't about to pussy out by spitting it up, but he sure as hell wouldn't eat another one.