sea urchin
Margulis and Schwartz, 1988, Asterias forbesi, a starfish. Arm radius of adult = 130mm.
Margulis and Schwartz, 1988, Morphology of the starfish, Asterias forbesi. [Photographs by W. Omerod; drawing by E. Hoffman, information from H. B. Fell.
Margulis and Schwartz, 1988