ABC

Syncarids were already a diverse group in the Paleozoic, especially during the Carboniferous and the lower Permian on the Laurentia supercontinent, and later on Gondwana in the PermoTriassic (Schram, 1981; 1984). The distribution of contemporary anaspidaceans covers only limited Gondwanian areas in Tasmania, Australia, New

Zealand, Chile, and Argentina. The disjunct distribution of numerous bathynellid genera results from a Gondwanian origin. Chilibathynella and Atopobathynella occur in Chile, Australia, and New Zealand; the sister groups Parvulobathynella and Acanthobathynella are distributed in South America and the Ivory Coast; Thermobathynella is known from Amazonia and Central Africa, Cteniobathynella from central African area, Israel, and Brazil, and Austrobathynella from the southern parts of Africa and America. The history of the closely related genera Texanobathynella and Iberobathynella is related to the opening of the northern Atlantic. The Iberobathynella group is endemic to the Iberian Peninsula, while Hexabathynella exhibits a cosmopolitan distribution from Brazil, California, Iberian Peninsula, Bulgaria, Corsica, to Madagascar, Australia, and New Zealand. On a large scale, the Parabathynellidae display a worldwide distribution from temperate to tropical areas. The Bathynellidae occupy more limited regions of the globe, mainly in the temperate northern hemisphere as well as some local areas of the southern hemisphere. Therefore, plate tectonics has played a major role in the distribution and the evolution of the Syncarida through vicariance. According to Schminke (1981), the Syncarida have a freshwater origin. In contrast, other authors (Boutin &

Coineau, 1987; Camacho & Coineau, 1989; Coineau, 1996; Guil & Camacho, 2001) claim that freshwater Syncarida are derived from marine ancestors. These ancestors lived in the interstitial littoral of the Tethys Sea before the break-up of Pangea and of Gondwana, and colonized subterranean freshwater at the end of regressions mainly in the Jurassic and Cretaceous. Most of the extant species are located in areas formerly covered by Tethys gulfs and co-occur with other interstitial crustaceans of marine origin. Paleogeographic data also strongly indicate a marine origin. Tethys regressions, as well as orogenesis in some regions of the world, provide an understanding of the evolutionary history of the Syncarida.