Water-vascular system

The vessels of the water vascular system end in tube feet. The water vascular system generally has one madreporite. Others, such as certain Euryalida, have one per arm on the aboral surface. Still other forms have no madreporite at all. Suckers and ampullae are absent from the tube feet.

Nervous system

The nervous system consists of a main nerve ring which runs around the central disk. At the base of each arm, the

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