The Echinoid Directory

Rhopalocidaris Mortensen, 1927, p. 272

Diagnostic Features
  • Tests generally very small (< 20 mm diameter).
  • Apical disc dicyclic; genital plates similar in size. Plates sparsely tuberculate. About half the test diameter.
  • Interambulacra with large primary tubercle; tubercles perforate and non-crenulate with incised areoles.
  • Scrobicular tubercles not much differentiated but forming continuous circles on ambital plates; areoles coalesced on adoral plates; contiguous on ambital plates. Extrascrobicular tubercles present only on interradial side.
  • A prominent naked zone runs down the interradial and perradial zones.
  • Ambulacra almost straight-sided. Pore-pairs oblique and non-conjugate with interporal partition about as large as a single pore. Marginal tubercle on each plate plus a smaller secondary tubercle; the rest of the narrow perradial zone is naked and furrowed.
  • Peristome similar in diameter to apical disc; 7-9 ambulacral plates, uniserially arranged in each series. Interradial plates confined to outer part of membrane.
  • Primary spines long and strongly thorned in the basal part and less so distally, where the shaft may be weakly ribbed. Cortical hairs dense and well developed in between large thorns.
  • Secondary spines club-shaped, not adpressed.
Recent, West Pacific.
Name gender feminine
Cidaris (Discocidaris?) hirsutispinus de Meijere, 1904, p. 20, by original designation.
Species Included
  • R. hirsutispina (de Meijere, 1904); Recent, Indo-West Pacific.
  • R. gracilis (Doderlein, 1885); Recent, Japan.
  • R. rosea Mortensen, 1928; Recent, Japan.
Classification and/or Status

Cidaroida, Cidaridae, Goniocidarinae.


Close to Goniocidaris in test form, especially in the development of prominent perradial and interradial naked zones. It differs in having club-shaped secondary spines, and in lacking discs on its primary spines.

Mortensen, T. 1928. A monograph of the Echinoidea. 1, Cidaroidea. C. A. Reitzel, Copenhagen.