|
The crown-of-thorns sea star, ''Acanthaster planci'', is a large, multiple-armed starfish (or seastar) that usually preys upon hard, or stony, coral polyps (Scleractinia). The crown-of-thorns sea star receives its name from venomous thorn-like spines that cover its upper surface, resembling the Biblical crown of thorns. It is one of the largest sea stars in the world. ''A. planci'' has a very wide Indo-Pacific distribution. It is perhaps most common in Australia, but can occur at tropical and subtropical latitudes from the Red Sea and the east African coast across the Indian Ocean, and across the Pacific Ocean to the west coast of Central America. It occurs where coral reefs or hard coral communities occur in this region. ==Description== The body form of the crown-of-thorns starfish is fundamentally the same as that of a typical starfish, with a central disk and radiating arms. Its special traits, however, include being disc-shaped, multiple-armed, flexible, prehensile, and heavily spined, and having a large ratio of stomach surface to body mass.〔 Its prehensile ability arises from the two rows of numerous tube feet that extend to the tip of each arm. In being multiple-armed, it has lost the five-fold symmetry (pentamerism) typical of starfish, although it begins with this symmetry in its life cycle. Adult crown-of-thorns starfish normally range in size from .〔Carpenter, R.C. (1997) (Invertebrate Predators and Grazers" ) In: C. Birkeland, ''Life and death of coral reefs'', Springer. ISBN 978-0-412-03541-8.〕 They have up to 21 arms. Although the body of the crown of thorns has a stiff appearance, it is able to bend and twist to fit around the contours of the corals on which it feeds. The underside of each arm has a series of closely fitting plates which form a groove and extend in rows to the mouth.〔"Crown of Thorns Starfish (Acanthaster Planci)." Crown of Thorns Starfish Videos, Photos and Facts. Web. 5 November 2014. The long, sharp spines on the sides of the starfish's arms and upper (aboral) surface resemble thorns and create a crown-like shape, giving the creature its name. The spines are stiff and very sharp, and readily pierce through soft surfaces. Despite the battery of sharp spines on the aboral surface and blunt spines on the oral surface, the crown-of-thorns starfish's general body surface is membranous and soft. When the starfish is removed from the water, the body surface ruptures and the body fluid leaks out, so the body collapses and flattens. The spines bend over and flatten, as well. They recover their shape when reimmersed, if they are still alive. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Crown-of-thorns starfish」の詳細全文を読む スポンサード リンク
|