ARCHASTER TYPICUS PDF

Description[ edit ] 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. This starfish is adapted to life on the sandy seabed, where it buries in the sediment during high tides and moves over the sediment surface during low tides. The underside is pale.

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Description Edit 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. This starfish is adapted to life on the sandy seabed, where it buries in the sediment during high tides and moves over the sediment surface during low tides.

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 which distinguishes it from the rather similar Astropecten polyacanthus which has similar habits and colouring. The spines, arranged in a marginal fringe, are short, flat and blunter than A.

It usually inhabits areas of the seabed with soft sediments including sand, silt and seagrass meadows. 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. However, in contrast to most other starfish, Archaster typicus performs pseudocopulation. 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.

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