bogleech:

Speaking of worms, my mind is still completely blown by Syllis ramosa, the polychaete annelid with a branching body. It lives only inside sea sponges, growing all through the sponge pores, and its anatomy is like a reverse hydra: one head, many butts.

Many MANY butts.

There is no known limit on how many butts this animal can have.

They’ve been recorded with butts in the thousands and probably just keep on growing them with the sponge host.