It’s amazing how informative an anus can be.

Take this sea urchin. The orange pucker in the middle of the spines is its “around-the-bum”, although zoologists would insist on writing that in Greek as “periproct”. The bright orange ring-piece is characteristic of this species, and marks it out as Diadema setosum, rather than any of the less rectally blessed species of Diadema.

If sea cumbers are an example of intelligent design, then God - sorry, an unspecified supernatural intelligence that somehow doesn’t infringe on the First Amendment - needs to lay off the acid. Echinoderms are what you get when you give evolution the number 5 and half a billion years to piss around.

You’ve simply got to love any animal that can vomit up its own bowels crap out its own gills to annoy predators.