The Echinoid Directory

Hemiphormosoma Mortensen, 1934, p. 162

Diagnostic Features
  • Test very delicate with flexible plating throughout.
  • Apical disc monocyclic; plating reduced with composite genital plates.
  • Ambulacra trigeminate, with large central element bearing a primary tubercle and two highly reduced adradial elements housing pore-pairs.
  • The two demiplates occluded from adradial and perradial sutures on adapical surface and often on adoral surface also.
  • Primary interambulacral tubercles present only close to the ambitus on both upper and lower surfaces, with sunken areoles.
  • Sphaeridia present on both demiplates.
  • Aboral spines ending in a simple point; in life bearing enlarged fleshy sacs.
Distribution
Recent, Indonesia.
Name gender neuter
Type
Hemiphormosoma paucispinum Mortensen, 1934, by original designation.
Species Included
  • Only the type species.
Classification and/or Status

Euechinoidea; Echinothurioida; Phormosomatidae.

Monotypic.

Remarks

Differs from Phormosoma in having only its ambital plates bearing enlarged primary tubercles. Both adapical and adoral plates by comparison are rather naked.

Mortensen, T. 1934. New Echinoidea. (Preliminary Notice.) . Videnskabelige Meddelelser fra Danks naturhistorisk Forening i Kobenhavn 98, 161-167.

Mortensen, T. 1935. A monograph of the Echinoidea. Volume 2, Bothriocidaroida, Melonechinoida, Lepidocentroida and Stirodonta. C. A. Reitzel, Copenhagen.