Spinulosida

Article By:

Mah, Christopher L. Department of Invertebrate Zoology, Smithsonian Institution, Washington, DC.

Last reviewed:June 2020

DOI:https://doi.org/10.1036/1097-8542.900561

An order of asteroids (sea stars) composed of the family Echinasteridae, including genera distributed in polar, temperate, and tropical regions and ranging from intertidal to deep-sea habitats. The Spinulosida includes one family, Echinasteridae, with eight nominal genera. Two of those genera, the cold-water Henricia (Fig. 1) and the tropical Echinaster (Fig. 2), include the greatest number of species in the family and are among the most widely distributed taxa in the Asteroidea. Echinaster includes approximately 30 species distributed throughout the shallow tropical Indo-Pacific and Atlantic oceans. Henricia includes 92 species distributed in cold-water habitats throughout the world's oceans, including Arctic, deep-sea, and Antarctic regions. Henricia occurs in every ocean basin, between the intertidal zone and depths of 1000 m (3300 ft). Most echinasterids have five rays, a small disk, and arms that are cylindrical in shape and circular in cross section. Some echinasterids, including Echinaster and Henricia, can reach moderately large sizes, having a diameter of up to 0.3 m (1 ft) across. The skeletal elements that compose the body wall in many echinasterids are similar in appearance, forming a netlike arrangement in many taxa. Most echinasterids have spinelets (small spines) that cover each plate. Spinelet shape varies from taxon to taxon; some spinelets are conical and thorny, whereas others are finer and more cylindrical. See also: Asteroidea; Deep-sea fauna; Echinodermata

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