Pawson, David L Department of Invertebrate Zoology, Smithsonian Institution, Washington, DC.
Fell, Howard B. Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts.
- Relation to humans
- Water-vascular system
- Nervous system
- Alimentary system
- Links to Primary Literature
- Additional Readings
A class of Echinodermata known as the sea urchins, also including sand dollars, sea biscuits, and heart urchins. In echinoids, the body is enclosed in a hard shell, or test, formed from regularly arranged plates that bear movable spines (Figs. 1 and 2). There are no arms, but radii are represented by five double rows of tube feet arranged as meridians between the upper and lower poles of the body.
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