That is a hyperiid amphipod. So this is basically the
inspiration for the alien in Alien. Yeah I think it's rare
that you see one animal wearing another animal as a hat. Not in
the deep sea. This would normally be a pelagic organism
of its own. It's a zooplankton that would be a filter feeder.
A salp or salp chain. These are planktonic tunicates. Um if
you've seen a sea squirt, you'll know what a tunicate is.
This is a relative that lives in the water column. It's
another kind of filter feeder.
Can you explain why it takes it over? It will capture those
salps and basically rip the inside of the salp out but keep
enough of the cells in the inside that it's more or less
alive and then uses the salp as its own little house.