Differs from Cystechinus and Urechinus in having apical disc with four distinct genital plates, each with a gonopore. Unique in having a sunken test adapically in females associated with brooding, and ribbed sphaeridia. Periproct position and presence of a subanal fasciole similar to juveniles of Urechinus. Mooi & David (1996) provide a detailed analysis of this genus.
David, B. & Mooi, R. 1990. An echinoid 'gives birth', morphology and systematics of a new Antarctic species, Urechinus mortenseni (Echinodermata, Holasteroida). Zoomorphology 110, 75-89.
Mooi, R. & David, B. 1996. Phylogenetic analysis of extreme morphologies: deep-sea holasteroid echinoids. Journal of Natural History 30, 913-953.