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Echinothurioida
Echinothurioida is an order of sea urchins in the class Echinoidea. Members of this order are distinguished from other sea urchins by the combination of a flexible test and hollow spines. The membrane around the mouth contains only simple plates, in contrast to the more complex mouth parts of their close relatives, the Diadematoida. They are nearly all deep sea dwellers.
==Characteristics==
Echinothurioids have regular tests (shells) with ten columns of plates. These plates are fused in groups of three with a central primary plate and a half plate on either side. The edge of each group of plates overlaps the next one in the manner of tiles on a roof and this means that the test is flexible. These animals usually collapse to a disc-shape when brought to the surface. The primary tubercles which articulate with the spines are each perforated by a hole and the spines are hollow. The primary spines are usually long and are used to support the test and in locomotion. In many species, the secondary spines are tipped with poison glands and the urchins should only be handled with gloves. The fused plates continue to the edge of the jaws, covering the peristome membrane that surrounds the mouth. The mouthparts, known as the Aristotle's lantern, have simple plates and grooved teeth. The gills are relatively small, and in many species, entirely absent.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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