What phylum is the hydrostatic skeleton in?

Answer 1

A hydrotstatic skeleton is primarily found in most invertebrates spread across a variety of phyla. Some of them include:

annelids - earthworms
cnidarians - jellyfish
echinoderms - sea stars
nematodes - roundworms
platyhelminthes - flatworms

All it really requires is an incompressible fluid-filled interior sac. Or many. The ones I list above, however, make use of their hydrostatic skeleton at their primary ones, and have flexible enough exteriors to use them for movement and the like.

Even some things you wouldn't think would need them make use of a hydrostatic skeleton for brief periods. Some crabs and insects, for example, make use of a hydrostatic skeleton for support when they shed their regular exoskeleton during growth.

Hope that helps. Links below:

Answer 2

Just about all of them.

Even human beings have a hydrostatically supported structure. Um, you're a girl so you might not know about that.