Phymosomatoida

(invertebrate zoology) An order of Echinacea with a stirodont lantern and diademoid ambulacral plates.

An order of regular sea urchins, class Echinoidea, characterized by imperforate tubercles, complex ambulacral compounding in which one or more elements are occluded from the perradial suture, and a stirodont lantern with unfused epiphyses. They comprise two families.They first appeared in the Lower Jurassic and are probably paraphyletic, since they include the ancestors of camarodonts. The two extant genera are each known from a single species: Glyptocidaris, from a depth of 30–490 ft (10–150 m) around northen Japan, and Stomechinus, a common inhabitant of rocky shores around the Indo-West Pacific. They are epifaunal grazers. See also Echinodermata; Echinoidea.