Reminds me of the creature from the flick "Deep Rising"... Can imagine a larger, nastier version of it lurking in the deepest level of the oceans.
It's one animal. I believe it's related to the Starfish the way we're related to other mammals. While they have the same common ancestor as the starfish, they have been on divergent evolutionary paths for a millions years.
Bobbit Worm - Can grow to 10ft in length. Stuff movie monsters are created after. @54secs - Like straight from a movie. Poof, gone.