Differs from Urechinus and other Urechinina in having a marginal periproct and in having the posterior interambulacrum hardly differentiated and, most distinctly, by having the first two plates in all interambulacral zones highly reduced. It also differs in having a distinctly invaginated peristome. Mooi & David (1996) provide a detailed analysis of this genus. The three species vary only in slight details of pedicellarial structure and may well prove conspecific.
Mooi, R. & David, B. 1996. Phylogenetic analysis of extreme morphologies: deep-sea holasteroid echinoids. Journal of Natural History 30, 913-953.
A. Agassiz 1904. Reports on an exploration off the west coasts of Mexico, central and south America and off the Galapagos Islands. Memoirs of the Museum of Comparative Zoology at Harvard University 31.