Ephemeroporus undetermined

54. ** Ephemeroporus sp. (Fig. 5A–F) Localities and specimens found: 50 – 10♀, 2j; 51 – 4♀, 3♀ ov, 8j. Distribution and ecology. These unidentified individuals of Ephemeroporus were found in the root system of floating macrophytes together with E. barroisi (see Appendix 1). Remarks. These Ephemeroporus specimens require further careful study. It is possible that they belong to a new species still unknown. According to the complex of external features, these Vietnamese individuals do not correspond to any of the currently known species of the genus (Frey 1982b; Alonso 1987; Elmoor-Loureiro 2014; Sinev & Yusoff 2016; Korovchinsky et al. 2021b). First of all, they differ by a relatively long posterior basal spine on the postabdominal claw (about two-thirds of the length of the anterior spine) (Figs. 5A, D, E), as well as an unusually long lateral seta on the antennule (more than twice as long as the antennule) (Figs. 5A, B). None of the other species of Ephemeroporus have such long posterior basal spines on the claws and setae on the antennules (Frey 1982b; Alonso 1987; Elmoor-Loureiro 2014; Sinev & Yusoff 2016). With the presence of several denticles on the anterior margin of the labrum (Figs. 5A, C) and the absence of teeth on the posterior-ventral corner of the valves (Figs. 5A, F), this Ephemeroporus from Vietnam is similar to E. phintonicus (Margaritora, 1969) and E. tridentatus (Bergamin, 1939). However, apart from the general differences mentioned above, Ephemeroporus sp. does not have a group of enlarged marginal teeth proximally on the postanal part of the postabdomen (Figs. 5A, E), as in E. phintonicus and E. tridentatus (Frey 1982b). The appearance of the postabdominal claws in Ephemeroporus sp. (Figs. 5A, D, E) is very similar to that in Chydorus nitidulus (Sars, 1901), but the latter has a noticeably different shape and armament of the postabdomen, has a tooth on the posterior-ventral corner of the valves and does not have denticles on the anterior margin of the labrum (Frey 1982b).