The Echinoid Directory

• Test low and rather thin-plated.
• Apical disc and peristome about 50% test diameter; dicyclic (usually); plates generally covered in tubercles. Ocular pores rimmed. Sexual dimorphism in gonopore size; gonopores large and marginal in females, in part bounded by interambulacral plates.
• Interambulacra of relatively few plates (up to 8). Tubercles perforate and non-crenulate with sunken areoles. Scrobicular circle not strongly differentiated from other secondary tubercles; outside areole plate uniformly covered in secondary tubercles with narrow incised interradial suture and feeble pits at triple suture junctions.
• Ambulacra almost straight. Pore-pairs very small and oblique, with the two pores separated by a very narrow interporal partition. Primary and smaller secondary tubercle to each ambulacral plate. Pore zones not sunken.
• No naked perradial zone or pits developed.
• Peristome with well developed series of ambulacral plates.
• Primary spines long, cylindrical, with short collar and distinct neck. Shaft ornamented with irregular thorns and with dense fine hairs in between. In some species spines become spatulate distally.
• Oral spines simple; not widened or serrate.
• Secondary spines with swollen tip.

Recent; Subantarctic.

Cidaris nutrix Wyville Thomson, 1876, p. 62, by original designation.

• Only the type species.

Cidaroida; Ctenocidaridae.

Treated as subgenus of Ctenocidaris by Mortensen(1928).

The only character that distinguishes Eurocidaris from Ctenocidaris is that its oral primary spines are simple and undifferentiated; those of Ctenocidaris being decidedly serrate and spear-shaped.

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