Correct Response: D. A hydrostatic skeleton consists of layers of muscles and a pressurized fluid filled compartment that assist in the movement of soft-bodied animals. The muscles stretch and then contract, and movement is dependent on the pressure of the fluid. Annelids, such as earthworms, have a hydrostatic skeleton. Myriapods, such as jellyfish, (A) and insects (C), have exoskeletons with muscles attached internally that allow for movement. Sponges (B) have spiny spicules for structural support, but they lack muscles and do not have a hydrostatic skeleton.
