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.
Recent, Indonesia.
Name gender neuter
Hemiphormosoma paucispinum Mortensen, 1934, by original designation.
Species Included
  • Only the type species.
Classification and/or Status

Euechinoidea; Echinothurioida; Phormosomatidae.



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.