STARFISH. Echinoderms with a star-like or pentagonal body, with two or four row's of ambulacral feet or tentacles on the oral side. The body is covered with small, short spines, often arranged in groups. The nervous system is pentagonal, with nerves extending into the arms. Most of the species are bisexual; the young usually pass through a metamorphosis, the starfish budding out from the water-vascular system of the gluteus, bipinnaria, or brachio laria form, which previously passes through a morula, gastrula, and cephalula stage. Star fishes are covered with scattered pedicellarbe, pincer-like spines consisting of two prongs. Sense organs (splueridia ) are also present. Starfish have the sense of smell, which is supposed to he localized in the suckers at the hack of the eye plate.
Starfish crawl or glide by means of from two to four rows of slender tubular processes or `feet,' with a sucker at the end. These ambnla cral feet are thrust out, fastened to the bottom, and by means of them the body is warped or pulled along over mussel or oyster beds, rocks, or weeds, the arms being capable of slightly bending. At the end of each arm is the red eye, terminat ing the radial nerve. Starfish are very destruc tive to op6ters, clams, mussels. barnacles, snails, worms, and small crustacea. To devour an oyster or clam the starfish grasps both valves of the shell, and by persistently exerting a constant steady strain, finally fatigues the adductor mus cles closing the valves so that they slightly gap open. Then the stomach is protruded between
the shells or valves and the soft body of the mollusk is digested. The injury to the oyster beds of Rhode Island caused by starfish in one year was estimated at $100,000. See ECnINOnER MATA (and Plate) ; OYSTER.
Fossil starfish are found first in the Ordovician rocks, and they occur sparingly in later forma tions, with some increase in the Devonian and Carboniferous, but they are never of geological importance. Sonic Mesozoic sandstone forma tions of Middle Europe have furnished abundant casts, and they are found also in a few Tertiary localities. The Paleozoic species are grouped in the subclass Encrinasterhe, in which the ambu lacral ossicles alternate with each other along the middle line of the ambulacra; while the Mes ozoic and Tertiary species, and also the recent, are included in the Enasterhe, which have the ambulacral ossicles opposite each other.
Consult: P•omanes, Jellyfish, Starfish, and Sea Urchins (New York. 1S85) ; Mead, 29th Report Rhode Island rommissioners of Inland Fisheries (Providence, 1899).