Siamopsis gen. nov. urn:lsid:zoobank.org:act: F4387DB9-8A9E-44FB-8B7B-9F07A89C26DE Type species Siamopsis renateae gen. et sp. nov. (here designated) Diagnosis RV overlapping LV anteriorly, ventrally and posteriorly. LV in internal view with postero-dorsal plate. Posterior margin of RV recurved inwardly. Wouters organ on A1 present, aesthetasc ya long. Terminal segment of Mx1 palp cylindrical, very elongated (length> 2 × width). A2 with well developed claws, long natatory setae, with two t-setae in females. T1 with a-setae (b, c and d setae absent). T2 with d2 seta (d1 seta absent). CR reduced, flagellum-like, cylindrical in shape. Etymology The genus is named after the country “ Siam ”, the former name of Thailand, where the new taxa were discovered. The name is combined with the suffix of the existing generic name Cypridopsis. Differential diagnosis Siamopsis gen. nov. can be distinguished from other genera of the subfamily Cypridopsinae by the presence of a postero-dorsal internal plate of the LV and the morphology of the posterior inner valve margin of the RV, which is recurved inwardly. Additionally, it differs from its closest genus, Plesiocypridopsis Rome, 1965, by the presence of the A1 Wouters organ, the two t-setae of the female A2 (there are four t-setae in Plesiocypridopsis) and the morphology of the two large bristles (teeth bristles) on the Mx1 third endite, of which one bristle is smooth while the other one is serrated (both setae are serrated in Plesiocypridopsis). Species included Siamopsis renateae gen. et sp. nov., S. suttajiti gen. et sp. nov., S. conspecta gen. et sp. nov., S. khoratensis gen. et sp. nov., S. planitia gen. et sp. nov. Distribution Thailand (present study). Remarks The postero-dorsal plate of the internal LV bears tooth- or teeth-like tubercle(s) in several species of Siamopsis gen. nov. The position of these tubercles can vary from species to species, being on, for example, the margin or in the middle of the plate. The degree of the inward curve on the RV posterior margin is different among species. Therefore, these aspects are used as taxonomic characters for identification.

Published as part of Savatenalinton, Sukonthip, 2017, Siamopsis gen. nov. and five new species of the subfamily Cypridopsinae Kaufmann, 1900 (Crustacea: Ostracoda) from Thailand, pp. 1-39 in European Journal of Taxonomy 384 on pages 3-4, DOI: 10.5852/ejt.2017.384, http://zenodo.org/record/3839820