Echinozoa
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Echinozoa is a subphylum of free-living
echinoderm An echinoderm () is any member of the phylum Echinodermata (). The adults are recognisable by their (usually five-point) radial symmetry, and include starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers, as well as the sea ...
s in which the body is or originally was a modified globe with meridional symmetry. Echinozoans lack arms, brachioles, or other appendages, and do not at any time exhibit
pinnate Pinnation (also called pennation) is the arrangement of feather-like or multi-divided features arising from both sides of a common axis. Pinnation occurs in biological morphology, in crystals, such as some forms of ice or metal crystals, and in ...
structure. Their two extant classes are the
sea urchin Sea urchins () are spiny, globular echinoderms in the class Echinoidea. About 950 species of sea urchin live on the seabed of every ocean and inhabit every depth zone from the intertidal seashore down to . The spherical, hard shells (tests) of ...
s and the
sea cucumber Sea cucumbers are echinoderms from the class Holothuroidea (). They are marine animals with a leathery skin and an elongated body containing a single, branched gonad. Sea cucumbers are found on the sea floor worldwide. The number of holothuria ...
s.


See also

*
List of echinodermata orders This List of echinoderm orders concerns the various classes and orders into which taxonomists categorize the roughly 7000 extant species as well as the extinct species of the exclusively marine phylum Echinodermata. Subphylum Crinozoa Cla ...


References

Animal subphyla {{echinoderm-stub