The Echinoid Directory

• Test ovate and thin-shelled with only a faint anterior sulcus; very depressed in profile.
• Apical disc ethmolytic with four gonopores, but with the four genital plates apparently fused. In any case the madrepores extend to the posterior of the posterior ocular plates; central to slightly posterior.
• Ambulacra all similar; non-petaloid and flush; only the adapical-most five or so plates bearing pore-pairs and short cylindrical tube-feet; other plates with microscopic pores only.
• Peristome pentagonal and slightly overarched by labrum; wider than long.
• Labral plate elongate and wedge-shaped, tapering to posterior; extending to middle of second ambulacral plate. Shape of sternal plates not known, but presumably triangular. Episternals unknown.
• Periproct marginal.
• Subanal fasciole present in type species; broad. Absent in other species assigned to this taxon.
• Aboral plates with scattered primary tubercles over ambulacral and interambulacral plates. Sternal plates tuberculate.
• Ophicephalous pedicellariae with distinctive globular head with basal part of valves highly developed and blades reduced.

Recent, Indo-Pacific c. 500-2250 m.

Argopatagus vitreus A. Agassiz, 1879, p. 209, by original designation.

• A. vitreus Agassiz; Recent, Indo-West Pacific.
• A. planus (Agassiz & Clark, 1907); Recent, Japan.
• A. aculeata (Agassiz, 1898); Recent, Cocos Islands, East Pacific.
• A. multispina (Agassiz & Clark, 1907); Recent, Hawaii Islands.

Spatangoida, Micrasterina, ?Macropneustidae.

?

Argopatagus and Phrissocystis are similar in all respects other than that Argopatagus has a subanal fasciole whereas Phrissocystis does not. Mortensen (1950) believed that the two should be synonymized.

Mortensen, T. 1950. A monograph of the Echinoidea. V, Spatangoida 1. C. A. Reitzel, Copenhagen.