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Salteraster (Starfish )

This is a starfish dating back to the Paleozoic, characterized by five arms that give it its typical pentamerous symmetry. The arms are very broar and strong, with a circular section; they possess a single row of median dorsal plates, separated from the marginal plate by numerous papillae. Some of these plates, situated on the lower surface of the arm, bear trasversal furrows with robust spines. The madreporite is positioned on the dorsal region of the central disk; in echinoderms, this plate acts as a valve to make water flow into the internal vascular system. It is probable that salteraster, like some modern starfish, fed on animals with a shell, opening the valves of its prey by means of the podia with which its arms were equipped, and everting its stomach; the digestion of its prey therefore took place outside the body. In order to carry out this operation the animal had to stand over its prey, raising itself up on its arms; there is an example of a fossil preserved in this position. copyright 1986 by Arnoldo Mondadori Editore S.p.A, Milan Published by Simon&Schuster, Inc .