What you're looking at is one of the really bizarre amphipod.
That attacks salps, it starts eating them and then uses the remnants
of the salps to construct a house. The females will have eggs
that hatch and the young will eat this house eventually.
The amphipod is a really bizarre creature with large claw like appendages, and is kind
of a model for some of the deep sea monsters that show up in the movies.
It's a really frightening looking animal, they are very small
but if they were larger they'd be
extremely scary.