棘皮动物

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棘皮动物(echinoderm)

棘皮动物门海洋无脊椎动物（invertebrate，棘皮动物门〔phylum Echinodermata〕），特徵是内骨骼由钙化的小骨片组成，成体的体型呈五辐射对称。现存约6,000种，分成六类：毛头星（feather star）和海百合（sea lily，海百合纲〔Crinoidea〕）、海星（starfish，海星纲〔Asteroidea〕）、蔓星鱼（brittle star）、蛇尾（basket star，蛇尾纲〔Ophiuroidea〕）、球海胆（sea urchin，海胆纲〔Echinoidea〕）、海参（sea cucumber，海参纲〔Holothurioidea〕）和海雏菊（sea daisy，海雏菊纲〔Concentricycloidea〕）。广布於各大洋，从潮间带到最深的海沟都有。大多数棘皮动物具有无数称为管足的小突起，不同种类的管足形态各异，功能为运动、取食、呼吸、挖掘、抓握和感觉。运动由水管系统控制，藉筛板与外界相通，有5条辐射管，由此伸出侧管，辐射管的腹面分支即为管足。大部分棘皮动物以沈积或悬浮的微小生物或有机碎屑（活的或死的）为食，但许多海胆和海星以植物为食。

English version：

echinoderm

Any of various marine invertebrates (phylum Echinodermata) characterized by a hard spiny covering, a calcite skeleton, and five-rayed radial body symmetry. About 6,000 existing species are grouped in six classes: feather stars and sea lilies (Crinoidea), starfishes (Asteroidea), brittle stars and basket stars (Ophiuroidea), sea urchins (Echinoidea), sea daisies (Concentricycloidea), and sea cucumbers (Holothurioidea). Echinoderms are found in all the oceans, from the intertidal zone to the deepest oceanic trenches. Most species have numerous tube feet that are modified for locomotion, respiration, tunneling, sensory perception, feeding, and grasping. Movement of water through a water vascular system composed of five major canals and smaller branches controls extension and retraction of the tube feet. Most echinoderms feed on microscopic detritus or suspended matter, but some eat plants.