Three new species of Cyprettadopsini of subfamily Cypridopsinae (Crustacea: Ostracoda) from Northeast Thailand with discussion on characters in the tribe

A survey of the ostracod fauna in the Chi River Basin in three provinces (Maha Sarakham, Kalasin and Roi Et) of northeast Thailand uncovered three new species of the tribe Cyprettadopsini of the Cypridopsinae: Cyprettadopsis hanjavanitae sp. nov., C. kalasinensis sp. nov. and Pseudocypretta sangpradubae sp. nov. Apart from its different soft part morphology, P. sangpradubae sp. nov. can be obviously distinguished from other Pseudocypretta by the valve ornamentation with strong pits and densely arranged long setae.

The two new Cyprettadopsis species can be primarily discriminated from the type species, Cyprettadopsis sutura Savatenalinton, 2020, by their subtriangular and subovate carapace shape in, respectively, lateral and dorsal views. Cyprettadopsis hanjavanitae sp. nov. mainly differs from C. kalasinensis sp. nov. by soft parts aspects, especially the caudal ramus. The discovery of these three new species, together with a literature review, provides additional diagnostic features of the Cyprettadopsini.

Most of them include the dorsal subapical seta on the basal segment of the maxilla palp, the g seta on the third thoracopod, the pseudosegmentation on the natatory setae of the second antenna, and the color pattern on the valve surface. In addition, setae with thick bases, which are found on the valve surfaces of all species of Cyprettadopsini, have so far been recognized only in the Cypridopsinae. Although the occurrence of marginal septa is an interspecific variable feature in Pseudocypretta and Cyprettadopsis, the modes of appearance are specific to their genera.

Herein, the distinguishing features and a key to the genera of the Cyprettadopsini are updated, and Mixtadopsis franki (Ferreira et al., 2023) nov. comb. is introduced. Pseudocypretta sangpradubae sp. nov. is the second Pseudocypretta described from Southeast Asia, and the first one from Thailand. Currently, the number of Cypridopsinae species in Thailand is 15, belonging to six (of a total of seven) tribes, indicating the high diversity at the tribe level of this subfamily in Thailand.