Article
Article
Echinoidea
Article By:
Pawson, David L Department of Invertebrate Zoology, Smithsonian Institution, Washington, DC.
Fell, Howard B. Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts.
Last reviewed:December 2019
DOI:https://doi.org/10.1036/1097-8542.210900
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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