Leydigia (Neoleydigia) australis Sars, 1885

31. * Leydigia (Neoleydigia) australis Sars, 1885

Localities and specimens found: 15 – 1♀; 16 – 1♀ ov; 26 –1j.

Distribution and ecology. Leydigia australis is a representative of the genus from Australia, which has also been recorded in some countries of Southeast and South Asia, namely Thailand, Cambodia, Sri Lanka, India ( Fernando 1974, 1980; Maiphae et al. 2008; Tanaka & Ohtaka 2010; Rane 2011; Choedchim et al. 2017; Choedchim & Maiphae 2023). However, some of these detections are questionable and most likely relate to other species (see details in Remarks below) ( Chatterjee et al. 2013; Kotov et al. 2013b; Sharma & Sharma 2017). In Vietnam, L. australis was first discovered in the course of present studies of the meiobenthos ( Gusakov et al. 2014).

The lifestyle and ecology of the species have not been studied in depth. Obviously, like other members of the genus, L. australis belongs to the typical bottom-dwelling chydorids (Kotov 2006). The crustacean was recorded in the benthos of the open and overgrown littoral of lakes, in dams and other lentic water bodies ( Fernando 1974, 1980; Choedchim et al. 2017; Choedchim & Maiphae 2023). In our material, single individuals were found on the bottom of shallow, moderately vegetated areas of a natural lake and in the littoral of a small reservoir (see Appendix 1).

Remarks. The status of the Oriental populations of L. australis needs further study. According to the main external features, the individuals we found in Vietnam correspond to the diagnosis of this species given in the latest revision of the genus ( Kotov 2009). A little later, Kotov et al. (2013b) assigned L. australis to a species group whose Southeast Asian populations are possibly separate species requiring formal description. Chatterjee et al. (2013) noted that the Indian records of L. australis known at that time most likely refer to L. ciliata (Gauthier, 1939) . Described from Sri Lanka, subspecies L. australis ceylonica (Daday, 1898) ( Smirnov 1971) is now positioned as the valid species L. ceylonica (Daday, 1898) ( Chatterjee et al. 2013; Kotov et al. 2013a; WoRMS Editorial Board 2024). According to Chatterjee et al. (2013), a specimen from Cambodia listed by Tanaka & Ohtaka (2010) as L. australis also belongs to L. ceylonica .