Spatangoidea

Spatangoidea, an order of Sea-Urchins or Echinoidea including those in which the anal aperture opens outside of the "apical system" (q.v.), and is not on the extreme upper point of the shell or test, and which have neither external gills nor an internal series of jaws or teeth. It is divided into two sub-orders, the Cassiduloides (g.v.), and the Spatangoidea, of which the latter includes the more typical forms suoh as the common Heart-Urchin (Spatangus purpureus), the common Chalk fossils, Micraster and Echinocorys.