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Sea urchins or urchins, sometimes cried sea hedgehogs, are smaa, spiny, globular animals which, wi thair close kin, such as saund dollars, constitute the class Echinoidea o the echinoderm phylum.

Sea urchin
Temporal range: Ordovician–Present
Tripneustes ventricosus (West Indian Sea Egg-top) and Echinometra viridis (Reef Urchin - bottom).jpg
Tripneustes ventricosus an Echinometra viridis
Scientific classification e
Kinrick: Animalia
Phylum: Echinodermata
Subphylum: Echinozoa
Cless: Echinoidea
Leske, 1778
Subclasses