Chydorus parvus Daday 1898

43. * Chydorus parvus Daday, 1898 Localities and specimens found: 50 – 2♀, 2♀ ov; 51 – 12♀, 11♀ ov, 3♀ em, 11j. Distribution and ecology. Chydorus parvus is generally known from the Afrotropical and Oriental regions (Smirnov 1996; Kotov et al. 2013a). In the latter, it is one of the most common representatives of the genus. In some sources, it was previously indicated here under synonymous names, Ch. sphaericus var. parvus Daday, 1898 and Ch. robustus Stingelin, 1905 (Swar & Fernando 1979; Rajapaksa & Fernando 1982a; Idris 1983; Michael & Sharma 1988; Sanoamuang 1998; Maiphae et al. 2005, 2008; Chatterjee et al. 2013; Korovchinsky 2013; Kotov et al. 2013b; Van Damme et al. 2013; Sinev & Yusoff 2015; Lopez et al. 2017; Sharma & Sharma 2017; Choedchim & Maiphae 2023). There is also evidence of finds of this species in Central China (Ji et al. 2015) and the Australian biogeographic realm (Maiphae et al. 2008). Prior to the present study, Ch. parvus had not been recorded in Vietnam. The lifestyle and ecology of Ch. parvus are not yet fully understood. The species was recorded in a wide spectrum of water bodies: lakes, ponds, reservoirs, channals, rivers, streams, floodplains, rice fields, swamps, pools, etc. (Idris 1983; Sanoamuang 1998; Sinev & Yusoff 2015; Choedchim & Maiphae 2023). Some authors present it as a eurytopic species, occurring in almost all types of habitats (Rajapaksa & Fernando 1982a; Idris 1983). According to Sinev & Yusoff (2015), this chydorid is more abundant on submerged macrophytes. We found Ch. parvus only among the roots of floating macrophytes (see Appendix 1). Remarks. Kotov et al. (2013b) note that the status of Ch. parvus populations found outside the Oriental area should be revised.