. Text book of zoology. Zoology. Clans 2. Asteroidea. Order 1. Asterida. 133 being thrown out again from the mouthy for the anus plays only a subordinate part. The species of Starfish are numerous, and occur in all seas. The following may be cited as examples : 1. Asterias ruhens, a five-rayed form, witt tte tube-feet arranged in foui' rows, and each, foot fumislied witli a sucker. Very common in North European seas, occurring on the shores and to considerable depths. It is inimical to Oyster beds, also causing havoc by devoui-ing Fish caught in nets or on hooks. Those from deeper water attain
. Text book of zoology. Zoology. Clans 2. Asteroidea. Order 1. Asterida. 133 being thrown out again from the mouthy for the anus plays only a subordinate part. The species of Starfish are numerous, and occur in all seas. The following may be cited as examples : 1. Asterias ruhens, a five-rayed form, witt tte tube-feet arranged in foui' rows, and each, foot fumislied witli a sucker. Very common in North European seas, occurring on the shores and to considerable depths. It is inimical to Oyster beds, also causing havoc by devoui-ing Fish caught in nets or on hooks. Those from deeper water attain a breadth of 50 c/m., the littoral ones are much smaller. 2. Solaster, Starfish of considerable size, with a large number of arms (about ten), tube-feet with suckers, in two rows. In North European seas. Order 3. OpMurida {Brittle Stars). The arms, usually five in number, are long and narrow, and do not meet at their bases; the edge of the disc between each two arms is usually straight, or somewhat bulging. In addition, the dorsal walls of the arms, by a different arrangement of the ossicles, generally difier somewhat in appearance from that of the disc; so that they seem to be well marked off from this, especially when examined from above. They differ, further, from those of the Starfish, in the absence of ambulacral grooves; the ventral surface is flat, and usually covered with calcareous ossicles which lie ventral to the radial water-vessel; dorsal to it are vertebra- like ossicles, which constitute the chief part of the arm, and are similar to those of the Starfish, although developed somewhat differently. The tube-feet, which are without suckers, are arranged in two series on the ventral surface, near the margin of the arms; and on the disc, near to the mouth. The aboral surface of the arms is usually covered with large calcareous plates, that of the disc is generally soft, with larger or smaller calcifications. The arms are very flexible, and are capable of a serpentine
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1896
