Echi·no·derm

marine invertebrates with tube feet and five-part radially symmetrical bodies.

Phylum Echinodermata:

The echinoderms (or spiny-skinned animals) are a distinctive group of exclusively marine animals which as adults are mainly bottom-living. They occur from the shore to the deepest parts of the ocean, but because they lack a system for regulating the water and salt balance in their bodies they are excluded from low-salinity areas. One of their most striking features is the 5-rayed symmetry of the adult body, which can be seen to a greater or lesser degree in all subphyla which the group comprises. Another universal feature is the presence of a skeleton, lying beneath the skin, composed of [calcareous] plates which in some cases can be fused together to form a rigid shell (test). These creatures have tube feet, which are used for locomotion in some species, and for collection of food in others. All echinoderms have a mouth, not all of them have an anus. Most species have the sexes separate, but a few are hermaphrodite. Not all species reproduce exclusively by sexual means; some also reproduce by splitting of the parent body into parts (fission).

Examples would be starfish, sea urchins, and sand dollars.

(Source 3)

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