All echinoderms are marine organisms. In the larval stage, most echinoderms are bilaterally symmetrical. Most adults are radially symmetrical. They have a ventral mouth, an internal skeleton of calcium carbonate plates, and a water vascular system consisting of tube feet, radial canals, and a ring canal for movement.
Members of the class Crinoidea include sea lilies and feather stars. Members of the class Stelleroidea include sea stars and brittle stars. Members of the class Echinoidea include sea urchins and sand dollars. Members of the class Holothuroidea include sea cucumbers.
Spinal extensions of the skeleton protect echinoderms.
The water vascular system of echinoderms is responsible for their movement and ability to clean to surfaces for long periods of time.
Feeding & Digestion
Urchins are herbivores (they eat plants), starfish are predators and scavengers, and other feed on detritus (waste).
Echinoderms have an open circulatory system with cilia circulating the fluids through each arm.
Amoeboid cells carry wastes out of the body.
Gills on the skin exchange gases.
Echinoderms have a nerve ring around the central disc instead of a brain. Eyespots on the tips of arms sense light.
Echinoderms have the ability to regenerate new parts asexually. They also have separate sexes with sex organs in each arm. Sexual reproduction involves releasing gametes into the water (external fertilization).