Note:
Download free Adobe Acrobat Reader to view PDF files at the
Adobe web site,
or go to access.adobe.com
for free tools that allow visually impaired users to read PDF files.
Definition:
Any solitary marine benthic (rarely pelagic) invertebrates, belonging to the phylum Echinodermata, characterized by radial symmetry, an endoskeleton formed of plates or ossicles composed of crystalline calcite, and a water-vascular system. Includes echinozoans, asterozoans, crinozoans, and homalozoans subphylums. [Glossary of Geology, 4th ed.]