Chydorus pubescens Sars 1901

44. Chydorus pubescens Sars, 1901 Localities and specimens found: 50 – 7♀, 1♀ ov; 51 – 1♀. Distribution and ecology. Chydorus pubescens is considered circumtropical (Smirnov 1996; Maiphae et al. 2008; Kotov et al. 2013a), but there are doubts about this (see Remarks for details) (Kotov et al. 2013b; Sinev & Korovchinsky 2013; Van Damme et al. 2013). In the Oriental region, to date, Ch. pubescens has been recorded in several countries (Michael & Sharma 1988; Sanoamuang 1998; Maiphae et al. 2005, 2008; Tanaka & Ohtaka 2010; Chatterjee et al. 2013; Korovchinsky 2013; Kotov et al. 2013b; Van Damme et al. 2013; Sharma & Sharma 2017; Tiang-nga et al. 2020; Choedchim & Maiphae 2023). In Vietnam, so far, it has only been discovered in the south, in Cat Tien National Park (Dong Nai province) (Sinev & Korovchinsky 2013; present study). The lifestyle and ecology of the species are little studied. It was found in different lentic and lotic water bodies: rivers, streams, natural and man-made lakes, marshes, ponds, pools, peat swamps, etc. (Sanoamuang 1998; Maiphae et al. 2005; Sinev & Korovchinsky 2013; Choedchim & Maiphae 2023). Probably, Ch. pubescens is associated with aquatic vegetation (Tiang-nga et al. 2020). In our material, several individuals of this species were found only in the rhizosphere of floating plants (see Appendix 1). Remarks. Chydorus pubescens was originally described in Brazil (Sars, 1901). Populations of this species found outside the Neotropics, and in particular in the Oriental area, may in fact represent other closely related species and still remain to be reviewed (Chatterjee et al. 2013; Kotov et al. 2013b; Sinev & Korovchinsky 2013; Van Damme et al. 2013). For instance, Ch. cf. pubescens, recorded by Idris & Fernando (1981) and Idris (1983) from Malaysia, actually refers to a recently described new member of the genus in the region, Ch. idrisi (Sinev 2014).