The Echinoid Directory

• Apical system with scattered tubercles. About 45-50% test diameter. Ocular plates generally insert in large individuals. Gonopores opening at outer edge of genital plates.
• Interambulacral columns composed of 7-8 plates.
• Primary tubercles perforate and rather strongly crenulate; areoles ovate and slightly incised; confluent on adoral surface.
• Scrobicular ring differentiated; tuberculation outside rather heterogeneous.
• Ambulacra narrow; almost straight; with simple plating throughout. Pore-pairs non-conjugate; oblique with narrow interporal partition.
• Peristome with biserial ambulacral zones and interradial platelet series that reaches the mouth.
• On inner surface of peristome each ambulacral plate with a distally directed prong.
• Primary spines long and cylindrical with moderately long collar and either smooth or weakly ribbed shaft; no cortical hairs; adoral spines short, curved and strongly serrated.
• Secondary spines long and flattened; erect rather than adpressed around the base of the scrobicular spines.
• Pedicellariae large and consistently bivalved.

Recent, NE Atlantic.

Porocidaris purpurata Wyville Thomson, 1872, p. 302, by original designation.

• Only the type species.

Cidaroida; Histocidaridae.

Monotypic; subjective junior synonym of Histocidaris.

Distinguished from Histocidaris, which has a very similar test and peristome morphology, by its bivalved pedicellariae. Some of the spines of Poriocidaris have a longer collar, usually more than 10 mm in length, whereas the collar of spines of Histocidaris is generally shorter. As noted by Clark (1907), these differences are slight.

Clark, H. L. 1907. The Cidaridae. Bulletin of the Museum of Comparative Zoology at Harvard College, 51, 165-230, pls 1-11.

Mortensen, T. 1909. Die Echinoiden. Report on the Deutschen Südpolar-Expedition 1901-1903, 3 (3), 113 pp., 19 pls.

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