On a freshwater species of the genus Sanyuania Zhao and Han, 1980 (Crustacea,Ostracoda, Loxoconchidae) from Thailand,with a discussion on morphological evolution of the freshwater Loxoconchidae

The genus Sanyuania Zhao and Han, 1980 Zhao, G. and Han, D. 1980. “Late Quaternary brackish‐water ostracod faunas from the area to the west of Weishanhu Lake, Jiangsu and their significance.”. In Papers on Marine Micropaleontology, Edited by: Wang, P. 120–129. Beijing (China): Ocean Press.  [Google Scholar] is here transferred from the Cytherideidae to the Loxoconchidae, based on the morphology of valves and soft parts. Sanyuania segersi sp. nov., is described from a freshwater habitat, a river, in Thailand. This is the first record of this genus in Southeast Asia. The new species has a number of remarkable characters distinguishing it from other members in the genus and family: invicidont hinge, spearhead‐like protruding posterior extremity of carapace in dorsal view, subtriangular shape of carapace in lateral view, sieve plate without a central seta (sensillum) and an aberrant chaetotaxy of first and second antennae. The new taxon is compared with other recent freshwater loxoconchids [Cytheromorpha fuscata (Brady, 1869 Brady, G. S. 1869. Contributions to the study of the Entomostraca. IV. Ostracoda from the River Scheldt and the Grecian Archipelago.. Ann Mag Nat Hist ser 4., 3: 44–50.  [Google Scholar]), Elofsonia baltica (Hirschmann, 1909), Loxoconcha elliptica Brady, 1868, Loxoconcha galilea Lerner‐Seggev, 1968, Pseudolimnocythere hartmanni Danielopol, 1979 Danielopol, D. L. 1979. On the origin and the antiquity of the Pseudolimnocythere species (Ostracoda, Loxoconchidae).. Biol Gallo‐Hellen., 8: 99–107.  [Google Scholar], Pseudolimnocythere hypogaea Klie, 1938 Klie, W. 1938. Ostracoden aus unterirdischen Gewässern in Süditalien.. Zool Anz., 123: 148–154.  [Google Scholar]] using (1) phylogenetic analyses and (2) analyses of the chaetotaxy of the first antenna and second and third thoracopods, by comparison with an ontogenetic series of Loxoconcha japonica Ishizaki, 1968. The results from both types of analyses are congruent and reveal that Sanyuania segersi sp. nov., Pseudolimnocythere and Loxoconcha are in a more derived clade in the Loxoconchidae and are closely related to each other, whereas Cytheromorpha and Elofsonia are more ancestral.