The Trapeziidae and Domeciidae (Decapoda: Brachyura: Xanthoidea) in the Fossil Record and a New Eocene Genus from Baja California Sur, Mexico

Reconsideration of all fossils formerly referred to the Trapeziidae Miers, 1886, suggests that both the Trapeziidae and the morphologically similar Domeciidae Ortmann, 1893, are represented in the fossil record. Two fossil species formerly considered to be trapeziids are referred to the domeciid genus Jonesius Sankarankutty, 1962. New combinations include J. oligocenicus (Beschin et al., 2001) and J. planus (Müller, 1996); thus, the recognized geologic record of the Domeciidae extends from the Oligocene to Recent. The Trapeziidae is known from three Eocene genera, including the new genus and species described here, Archaeotetra inornata. Other Eocene occurrences include two species of Eomaldivia Müller and Collins, 1991, and one species of Tetralia Dana, 1851. A few Miocene species of Trapezia Latreille, 1828, and a Pleistocene occurrence have been reported. Members of both families are symbiotic with cnidarians, and this relationship appears to have been established by the Eocene in the case of the Trapeziidae and the Oligocene for the Domeciidae, based upon the tropical to subtropical distribution and the occurrence of the fossils in each family in coral-bearing rocks. Coevolutionary processes appear to have resulted in high degrees of specialization in some genera within the Trapeziidae.