The New Student's Reference Work/Starfish
Star′fish, the name for a number of marine animals having arms or rays arranged around a central disk. As these are symmetrically arranged, the animal is said to have radial symmetry. There are several varieties, but the common five-rayed starfish is the type. It is reddish, or yellow, in color, and those along the New England coast commonly vary from one inch to one foot in diameter. It lives on the sea bottom and crawls sluggishly by means of tube feet. It is often seen in shallow pools left by the retreating tide. The skin is stiffened with plates and nodules of lime. The mouth is in the center of the disk, on the under side, and the animals feed on decaying fish and other animal matter, as well as on small shelled mollusks. Their means of locomotion is peculiar. There are four rows of tube-feet in furrows along the lower sides of the arms. These tube-feet are filled with water and connected with a system of water tubes running through the body. On the back of every starfish may be seen a little rounded knob, which is porous and leads into the water-vascular system. From this tubercle, a tube leads downward to join a circular canal surrounding the mouth, and from this central canal a tube extends into each arm or ray. These latter canals are connected with the tube-feet and also with internal pockets, one for each tube-foot. The nervous system consists of a ring about the mouth and a nerve running from it into each arm. At the extremity of each arm is found a little red eye-spot which is sensitive to light. Some other starfish have 11 to 13 rays, and some resemble five-sided pin cushions in form. The brittle starfishes have a central disk, with long, slim, muscular rays by means of which they move. Their tube-feet are not developed. All starfishes possess the power of restoring, or regenerating, lost or injured parts. See Echinodermata and Sea-Urchin. Consult Romanes’ Jelly-fish, Starfish and Sea-Urchin.
STARFISH
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| COPYRIGHT 1904, BY C. B. BEACH | |
| SEA URCHINS AND STAR FISH. |
