Phylum Echinodermata

Characteristics
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.

Classification
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.

Protection
Spinal extensions of the skeleton protect echinoderms.

Movement
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).

Circulation
Echinoderms have an open circulatory system with cilia circulating the fluids through each arm.

Excretion
Amoeboid cells carry wastes out of the body.

Respiration
Gills on the skin exchange gases.

Nervous System
Echinoderms have a nerve ring around the central disc instead of a brain. Eyespots on the tips of arms sense light.