Asterias blastopore8/13/2023 The size varies from 10-20 cm in diameter though some forms may be much smaller or longer. In some genera, the number of arms may be more than five, for example, there are 7-14 arms in Solaster and more than 40 arms in Heliaster. The body consists of a central, pentagonal central disc from which radiate out five elongated, tapering, symmetrical spaced projections, the rays or arms. External Features of Asterias: (i) Shape, Size and Colour:Īsterias has a radially symmetrical and pentamerous body. Sea stars, in general, exhibit remarkable power of autotomy and regeneration.ģ. Many species of Asterias exhibit various types of biological relationships such as parasitism and commensalism, etc., with the members of different zoological groups. They move by crawling on the bottom, mostly at a rather slow rate.Īll sea stars are carnivorous and feed voraciously on almost any available slow moving or sessile animals, chiefly on polychaetes, crustaceans, molluscs and other echinoderms and even corpses. Most of them are nocturnal, remain quiet in day time and become active during night. The most species of Asterias are generally solitary but under certain ecological conditions, such as to avoid direct sunlight or excessive drying, many individuals may gather at some place for the purpose of protection. There occur about 150 species of Asterias all of which have different geographical distribution. The name starfish is somewhat misleading suggesting an organism to be like a star and fish but as Asterias lacks in both the characteristics, therefore, recently it is renamed as sea star.
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