The Echinoid Directory

Idiobryssus Clark, 1939, p. 173

Diagnostic Features
  • Test small (<12 mm) ovate without anterior sulcus; slightly concave adapically with supramarginal periproct and small subanal heel.
  • Apical disc anterior of centre; no gonopores; plating obscure.
  • Frontal ambulacrum narrow and flush, with simple tube-feet only.
  • Petals more or less flush; narrow and straight, with parallel-sides and little perradial space. Anterior petals widely diverging and about 50% longer than posterior petals.
  • Peristome D-shaped and downward-facing; labral plate not projecting.
  • Plastron plating obscure, but labral plate apparently rather short and wide, not extending beyond first ambulacral plate. Sternal plates fully tuberculate.
  • Periproct supramarginal.
  • Subanal fasciole present; peripetalous fasciole present, not indented between ambs.
Recent, East Pacific.
Name gender masculine
Idiobryssus coelus Clarck, 1939, p. 173, by orginal designation.
Species Included
  • Only the type species.
Classification and/or Status

Spatangoida, Micrasterina, Brissidae.

Monotypic. Incertae sedis.


The fact that the periproct is supramarginal and there are no gonopores indicates that this is based on a juvenile. The peripetalous and subanal fasciole, together with the fact that the labral plate is relatively short indicates this belongs to the Brissidae.

Clark, H. L. 1939. A remarkable new genus of sea-urchin (Spatangidae). Allan Hancock Pacific Expeditions 2, 173-176.

Clark, H. L. 1948. Report on the Echini of the warmer Eastern Pacific, based on the collections of the Velero III. Allan Hancock Pacific Expeditions 8 (5),