Bronn, 1860
The adult body of Echinoidea (sea urchins and sand dollars) is globular or discoidal, and often shows secondary bilateral symmetry. The (endo)skeletal plates are fused as a solid test. Movable spines present. Adults are benthic.
The larva of Echinoidea is called an echinopluteus larva [Echinoidea pluteus ]. Typically, the larval spine-like arms of Echinoidea are more or less directed and not "flat" as in the pluteus larvae of brittle stars [Class Ophiuroidea]. The pluteus larva stays in the plankton for some time, depending on the species. For instance, the larval stage of Psammechinus miliaris (common in the North Sea) may last from ca. four weeks (Jensen, 1969) to about 40 days.
Echinopluteus larvae are recognised in the key, but not identified to species.