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The Pearlfish is an unusual species of fish in that instead of evolving ways to defend itself from predators it instead decided that it would live inside the anuses of various Invertebrate such as starfish, clams but ideally: Sea Cucumbers.
Pearlfish find the assholes of Sea Cucumbers such an ideal habitat that although they're typically independent fish; they been found to live in communities as big as 15 members... All living inside the Anus of a single large Sea Cucumber.
Luckily for the fish the Sea Cucumber is one long "channel" and so when the creature breaths in to eat out of it's anus the pearl fish gets the scraps and if the Sea Cucumber "clenches" it's anus the Pearl fish simply sticks it's thin little tail into the creatures anus to suffocate it until it open's back up to let the fish inside.
The point I'm trying to get at is: you will never be more degenerate than nature.