There is only a single specimen of this monotypic genus, and that is poorly preserved, leaving much unknown. In having confluent posterior petals it resembles certain species of Brissopsis and Metalia. The most important difference between these two species is that the plastron of Metalia has episternals only slightly smaller than the sternals and separated by a U-shaped suture (convex anteriorly) whereas in Brissopsis the episternals are less than half the size of the sternals and are separated by a V-shaped suture (pointing posteriorly). The only known specimen has been redescribed by Kier (1984) and does not show plastron features clearly.
Fischer (1985) described a second species from the Miocene of Costa Rica, which Durham (1961) had earlier assigned to Brissopsis sp. nov. The plastron plating of Durham's specimen, though poorly preserved, is more suggestive of Brissopsis than Metalia.
Tentatively, therefore, Fernandezaster is treated as a synonym of Brissopsis.
Kier, P.M. 1984. Fossil spatangoid echinoids of Cuba. Smithsonian Contributions to Paleobiology 55, 1-336.
Fischer, R. 1985. La fauna de la Formacion Turrucares (Mioceno, Valle Central, Costa Rica). Geologica et Palaeontologica 19, 191-225.