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sea-star
Class
Asteroidea
[
starfish
]
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| Photo by : Nikita |
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| Photo by : John |
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The asteroid body has the form of a somewhat flattened star with arms (rays) usually numbering 5 or a multtiple of 5, rearely 6 or some other number,
each in contact with 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 2 arms,
and opening 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 the 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 pincing small objects, a modification of 2 or 3 spines.
[
National Audubon Society Field Guide of North American Seashore Creatures.
]
The stars can regenerate lost arms. Wnen 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, regeneration 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 the star.
[
National Audubon Society Field Guide of North American Seashore Creatures.
]
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