Sea stars and sea urchins operate their tube feet by

A) a hydraulic system that regulates water pressure.
B) cilia transporting hemolymph from chamber to chamber.
C) sticky threads leading from the mouth.
D) actin and myosin fibers that slide and give muscle actions to the five arms or "rays."
E) an extensive net of nerve and muscle cells.

Hydraulic System

A technology in engineering that uses pressurized fluid to produce or transmit power.

Tube Feet

Small, flexible, hollow appendages used mostly for movement and feeding by echinoderms, such as sea stars and sea urchins.

Water Pressure

The force exerted by water on the surrounding environment, which increases with depth and is a critical factor in aquatic ecosystems and engineering.