Archaster typicus (J. Mller & Troschel 1840)
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This animal including the starfish-shaped radial symmetry and have five or more arms. Skeleton in the sea star is not working to help the movement, but they serve only protection. They move with the water vascular system. They depend on tube feet are located on the ventral arm snake star, whose function is to assist the movement and feeding. Starfish are invertebrates that move freely by using the tube feet, crawling along the sea floor in a low enough speed for most species. On the surface of his skin are the thorns of various sizes. These animals are often found on the beach. Another feature is a branched organs to the whole arm. mouth below the surface called the oral surface and anus are located on the upper surface (aboral surface). Tube feet are on the oral surface. While on the surface of the aboral anus but there is also madreporit. Madreporit is a kind of sieve that has holes in connecting with the sea water and water vascular system hole sex. Archaster typicus is a five-limbed star with long, slightly tapering arms with pointed tips. Occasionally three, four, or even six-armed individuals occur. Adults grow to 12 to 15 centimetres (4.7 to 5.9 in) in diameter, with males often being smaller than females. This starfish is adapted to life on the sandy seabed, where it spends much of its time buried in the sediment. The general colour is grey or brownish, variously marked with darker and lighter patches, sometimes forming a chevron pattern. The underside is pale. The body is slightly inflated and there is a whitish madreporite near the centre of the disc. The small armour plates that cover the upper surface of the arms are lined up in neat parallel rows. Archaster typicus is found in the western Indian Ocean and the Indo-Pacific at depths 1.5 meters. They usually lives in sandy areas in teh bottom of sea. Archaster typicus is a detritivore and eats detritus and anything else edible it comes across. To feed, it everts its stomach through its mouth which is situated centrally on its underside. The food item is engulfed and brought inside the starfish when its stomach is returned to its normal position Like other starfish, Archaster typicus is a broadcast spawner, the male and female starfish each liberate their gametes into the sea where fertilisation takes place. However, in contrast to most other starfish, Archaster typicus performs pseudocopulation. About two months ahead of spawning the starfish begin to congregate, with males in particular becoming more mobile. A starfish can tell whether another is male or female, probably by chemotactic recognition. On recognizing a female, the male will climb on top of her and may remain there for two months. The female can move about and feed but the male is more restricted in his activities. During this time they synchronize their gonadal activity so that when the female is ready to spawn, so is the male. When she releases her eggs, he releases his sperm almost simultaneously thereby increasing the chances that successful fertilisation will take place.