The phylum Echinodermata (Greek meaning echino, “spiny”; derma, “skin”) contains about 7,000 living species. They are almost strictly marine expect for a few species that tolerant brackish-water. Echinoderms are found in all of the oceans. They have a basic pentamerous radial symmetry, and echinoderms contain a water vascular system that consists of a complex series of fluid filled canals that extends through the rays or arms of the animal.

References:

Brusca, R.C., and Brusca, G.J. (2003). Invertebrates. Library of Congress Catologing-in-Publication-Data: USA.

Kozloff, Eugene N. (2000). Seashore Life of the Northern Pacific Coast. University of Washington Press: Seattle and London.