What are animals with hydrostatic skeletons able to do that animals with exoskeletons or internal skeletons ca?

Elongate

A hydrostatic skeleton or hydroskeleton is a structure found in many cold-blooded organisms and soft-bodied animals consisting of a fluid-filled cavity, the coelom, surrounded by muscles. The pressure of the fluid and action of the surrounding muscles are used to change an organism's shape and produce movement, such as burrowing or swimming.Some examples are soft bodied animals such as sea anemones and earthworms. Hydrostatic skeletons have a role in the locomotion of echinoderms (starfish, sea urchins), cnidarians (jellyfish), annelids (earthworms), nematodes, and other invertebrates. They have some similarities to muscular hydrostats.

Elongate.

Animals with hydrostatic skeletons are things like worms, jellyfish.
People have internal skeletons, we are able to crawl and grow without replacing our skeletons.
Crabs have exoskeletons, and they live in aquatic environments.
Therefore, elongate is the answer.