The edges of these grooves are provided with two or three rows of movable calcareous ambulacral spines. Five narrow ambulacral grooves, one on each arm, run orally from the five-rayed aperture to the tip of the arms. This opening is surrounded by a membranous peristome and it also possesses five groups of oral papillae. Body is covered by a hard and tough covering containing numerous calcareous ossicles.Īt the middle of the central disc, on the oral surface, a five-rayed aperture called mouth or actinosome (Fig. The imaginary lines dividing the central disc and the arms are called the radii and the intervening regions between the radii are called inter-radii. The upper, aboral or abactinal surface is convex and much darker, while the lower, oral or actinal side is flat and less pigmented. The body exhibits radial symmetry and has two surfaces. The lengths of the arms are two or three times the diameter of the disc. The arms are conspicuously broad at their bases and they gradually taper towards the tip. The body consists of a central disc and five symmetrically placed arms (or rays). The body of Asterias is flattened in the oral-aboral axis and has a five-pointed star- shaped body (Fig. panceri, where positive response to light is observed. A few exceptions are the Asterias rubens, A. Majority of the forms are photonegative and prefer to live in shaded areas. They are carnivorous and predacious animals, preferring mainly bivalves as food. They are quite abundant on various types of sea-bottom but prefers a rugged and rockbound coast, where they can hide very easily and lead a sluggish life. All the species under this genus are benthic animals, as they inhabit the bottom of the sea. Asterias is a marine and widely distributed member of echinoderm.
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