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post #1 of 1 (permalink) Old 05-25-2002, 02:27 PM Thread Starter
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Short-spined Sea Star

Short-spined Sea Star
Pisaster brevispinus


Description: The Short-spined Sea Star is in the class Stelleroidea, subclass Asteroidea. The asteroids include the sea stars, also called starfish, a term considered inappropriate by biologists, who would like to see the word “fish” reserved for finny vertebrates. The asteroid body has the form of a somewhat flattened star, with arms (rays) usually numbering 5 or a multiple of 5, rarely 6 or some other number, each in contact with the adjacent arms where it joins the central disk. The surface of the central disk has the anus in the center, the sieve plate near the junction of two arms, and openings of sex ducts at each juncture of adjacent arms. The upper surface of each arm has the spines and other features of the species, and an eyespot, usually red, at the tip. The underside of a sea star has the mouth in the middle of the central disk, and an open groove from the mouth to the tip of each arm. 2 or 4 crowded rows of tube feet lie in each groove. In some sea stars there is a special skeletal structure for pinching small objects, a modification of 2 or 3 spines. These pinchers (pedicellariae) may be shaped like small tweezers or pliers, or flattened like the jaws of a vise. Sea stars travel on their tube feet. Tube feet with suckers reach ahead and attach, drawing the star in that direction while others detach, reach farther forward, attach, and so progress. Tube feet of burrowing sea stars lack suckers, and merely push the animal along.The feeding of sea stars varies greatly with the species, but in many cases involves the extension of the forepart of the stomach out through the mouth to envelop the food.Sea stars can regenerate lost arms. When an arm is damaged, it is shed at a point close to the central disk, even though the damage may be near the tip, a process called autotomy. In most species, after autotomy the cut surface heals over, regeneraion of a new arm begins, and the autotomized limb dies. However, there are a few sea stars in which autotomy is spontaneous; not only does the star regenerate a limb, but the limb regenerates a star.

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Stephanie

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