The Echinoid Directory

Orthanthus Mortensen, 1948, p. 34

Diagnostic Features	As for Clypeaster except with thin margins and broad, flat oral surface. Petals straight or expanding distally. No double wall around margin.
Distribution	Recent, Caribbean
Name gender	masculine
Type	Clypeaster euclastus Clark, 1941, by original designation
Species Included	Mortensen included two other species in this taxon, Clypeaster cyclopilus H. L. Clark & C. ravenelii A. Agassiz, both Recent. The oldest fossil Clypeaster, Biarritzella marbellensis Boussac, 1911, appears to belong to this subgenus, which would make Biarritzella a senior subjective synonym of Orthanthus. However, Biarritzella is currently based on material that is too poorly known.
Classification and/or Status	Clypeasteroida; Clypeasterina; Clypeasteridae Subjective junior synonym of Clypeaster Lamarck, 1801.
Remarks	Like Platyclypeina but with petals open distally. Treated as a subgenus of Clypeaster by Mortensen (1948). Mortensen, T. 1948. A Monograph of the Echinoidea IV.2 Clypeasteroida. C. A. Reitzel, Copenhagen.