The Diadematoida are an
order of
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. They are distinguished from other sea urchins by the fact that their spines are hollow, or at best have an open mesh at the core, and by the presence of 10 buccal plates around the mouth. Their tests can be either solid or flexible.
Taxonomy
References
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Extant Early Jurassic first appearances
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