Okay, so sea apples (generae Pseudocolochirus, Paracucumaria) are a type of sea cucumber, which yes, I know, terribly fucking helpful.
Like if a slug and a cucumber had babies capable of spitting their guts at you if you upset them!
Weirdly enough, these guys are actually echinoderms, so they’re up there with urchins and starfish.
Anyway, sea apples are a bit more colorful and a lot more round than most sea cucumbers, so they got a really fantastically imaginative name.
Above: A sea apple with its feeding tentacles extruded.
Sea apples filter plankton from the water with those suckers. When they’re in danger, or sleeping, they schlorp them right back into their bodies like the picture up top shows.
Those little yellow nubbies running down its sides in stripes are tube feet. Tube feet!
Above: Some motherfuckin’ tube feet, aw yeah. (Motherfuckin’ tube feet attached to a starfish.)
Sea apples mostly use theirs to keep themselves attached to shelter and the substrate, but they are capable of using them to travel. They are also capable of spitting their guts out if a predator keeps harassing them once they’ve sucked in their tentacles, but they’re not really capable of running away on their tube feet.
Above: A starfish running away on its tube feet.
Below: A sea apple giving it the good old college try.
What they can do when they really need to get gone is suck in their tentacles, retract their tube feet, inhale in a shitload of water, and just nope-roll the fuck out of dodge on the next wave.
If you ever see these guys in an aquarium, they’ll probably have the tank to themselves. It’s way easier to feed them this way (plankton-eaters are generally kind of a pain in the ass to keep healthy with other animals present), and also if something gets them to spit out their guts, they might also just spit out a load of poison with it, because nope-rolling isn’t the fastest way anything’s ever escaped in the ocean, and they need something to buy time.
If they do this in the ocean, no big. If they do this in an aquarium, it’s kind of like just screaming “Ah, motherland!” and stabbing a map with a Swiss army knife.