Question

a hydrostatic skeleton is a

skeleton that consists of fluid held under pressure in a closed body compartment.
hardened internal skeleton buried in soft tissues.
hard covering deposited on an animals surface.

Explanation:

A hydrostatic skeleton is composed of fluid - filled closed compartments that use fluid pressure for support and movement. The other options describe endoskeletons (hardened internal skeleton) and exoskeletons (hard covering on surface) respectively.

Answer:

skeleton that consists of fluid held under pressure in a closed body compartment.