Carpoids

(paleontology) An assemblage of three classes of enigmatic, rare Paleozoic echinoderms formerly grouped together as the class Carpoidea.

The common name for four extinct classes of primitive echinoderms that have a flattened theca or body lacking radial symmetry. These enigmatic fossils were originally classified together in the class Carpoidea, but more recent echinoderm researchers have assigned them to four separate classes in the subphylum Homalozoa: the Stylophora (or Calcichordates), Homoiostelea, Homostelea, and Ctenocystoidea. These four classes include about 50 genera that range from the Early or Middle Cambrian to the Late Carboniferous. Carpoids have a flattened theca that varies from asymmetrical to nearly bilaterally symmetrical (see illustration) and is made up of sutured, multiporous, single-crystal, calcite plates like those found in other echinoderms. Three of the classes have a long plated appendage attached to the theca that was used for locomotion and, in the Stylophora, also for feeding. Carpoids were apparently mobile, bottom-living or shallow-burrowing, detritus or suspension feeders, sifting out small food particles from the top layer of soft sediment or from the surrounding seawater. Because of the distinctive skeletons, most researchers consider carpoids as true echinoderms, although they seem only distantly related to other fossil and living echinoderms that have well-developed pentameral symmetry. See also Echinodermata; Homalozoa.

convex upper side of the plated theca showing part of the attached, tapering appendage used for locomotion and feeding at the bottom.">
Enoploura popei, a stylophoran carpoid from the Late Ordovician of Ohio. (a) Concave lower side and (b) convex upper side of the plated theca showing part of the attached, tapering appendage used for locomotion and feeding at the bottom.