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Starfishes. A term in its widest application embracing all the echinoderms comprised in the orders Ophiuroidea and Asteroidea, but more commonly restricted to the members of the latter order, of which the common genus Asterias may be taken as the type. The starfishes proper are covered with a tough leathery skin beset with prickles, and have the form of a star, with five or more rays radiating from a central disc. In the middle of the under surface of the disc is situated the mouth, opening into a digestive system which sends prolongations into each ray. If the prickly skin be removed it will be seen to be supported by a series of plates beautifully jointed together. On the under surface of each ray the plates exhibit a series of perforations, through which, in the living state, the ambulacra or tubular feet can be protruded so as to effect locomotion. Starfishes are found in almost all tropical, European, and American seas, and some species are found as far north as Greenland.