Asteroidea

Article By:

Campbell, Andrew C. Department of Biological Sciences, Queen Mary College, University of London, London, United Kingdom.

Last reviewed:March 2020

DOI:https://doi.org/10.1036/1097-8542.056600

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• Asteroidea, published June 2014:Download PDF Get Adobe Acrobat Reader

A class of the asterozoan group of the phylum Echinodermata, often known as sea stars or starfish. Members of the class Asteroidea, that is, asteroids, are notable echinoderms with a star-shaped body plan (Fig. 1). Unlike members of their sister asterozoan class, the Ophiuroidea (brittle and basket stars), the arms of asteroids are not sharply demarcated from the rest of the body, the ambulacral ossicles never fuse to form vertebrae, and the tube feet are locomotory (Fig. 2). These tube feet are usually suctorial and emerge from an open ambulacral groove. The dominant growth gradients cause the skeletal ossicles to lie in longitudinal rows known as series (for example, adambulacral series, ventrolateral series, and inferomarginal series). Asteroids range in size from about 10 mm to 1 m (0.4 to 40 in.) across. Many sea stars are brightly colored and attractive animals, but some are dowdy and cryptic. Their conjugated carotenoid pigments fade on preservation. Like most echinoderms, sea stars have a life span of about 5 years. See also: Carotenoids; Echinodermata; Ophiuroidea

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