The Mothership Are these the same sort of 'shipworms' that eat into wooden hulled vessels like barnacles do? Cause Jesus it seems like this mollusk(?) would sink most wooden ships.
Come on POETV biologists and oceanographers, help The Mothership out, I need to know.
Ninehells While little ones have the nickname "termites of the sea" for the reason you describe, big species are largely muck-dwelling chemovores that rely on symbiotic critters to eat and digest things for them.