The Echinoid Directory

• Test small, ovate; thin-shelled.
• Apical disc in males standard, with four gonopores. In females, highly modified for brooding (see David & Mooi 1990).
• Ambulacra all similar with minute pores only; all flush.
• Peristome subcentral and a little depressed; subcircular.
• Plastron plating orthosternous; first sternal plate enlarged and followed by a pair of nearly symmetrical episternal plates.
• Scattered tubercles uniformly distributed over the entire aboral surface.
• Periproct marginal to supramarginal.
• Subanal fasciole present, starting on Interambulacral plates 5b2/5a3.
• Sphaeridia with ribbed ornament.

• A. mortenseni (David & Mooi 1990); Recent, Antarctic.
• A. nordenskjoeldi (Mortensen, 1905); Recent, Antarctic.
• ? A. drygalskii (Mortensen, 1905); Recent, Antarctic.

Holasteroida, Meridosternata, Urechinina, ?Urechinidae.

Monotypic.

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.