Ilyocryptus raridentatus Smirnov, 1989

5. * Ilyocryptus raridentatus Smirnov, 1989

Localities and specimens found: 8 − 2♀, 3♀ ov, 2♀ em, 1j; 25 − 25♀, 21♀ ov, 50♀ em, 95j; 26 − 51♀, 33♀ ov, 26♀ em, 116j; 27 −1j; 32 − 1♀, 1j.

Distribution and ecology. Ilyocryptus raridentatus s. str. was described from Australia in insufficient specification and has only recently been redescribed in detail ( Kotov & Štifter 2006; Dadykin et al. 2024a). The currently known range of the species, in addition to Australia, covers a number of countries in Southeast and East Asia, penetrating north up to Korea, Japan and the Russian Far East ( Kotov & Sanoamuang 2004b; Kotov & Štifter 2006; Kotov et al. 2011, 2012, 2024; Korovchinsky et al. 2021b; Choedchim & Maiphae 2023; Dadykin et al. 2023, 2024a). In Vietnam, this ilyocriptid was first recorded in the course of the present studies of the meiobenthos as I. cf. raridentatus ( Gusakov et al. 2014, 2024).

This crustacean is a typical bottom dweller, like other representatives of the genus. It is found in various lentic and lotic water bodies (swamps, puddles, ponds, lakes, reservoirs, rivers, river floodplains, etc.) but its ecological preferences are still not fully understood ( Kotov & Štifter 2006; Choedchim & Maiphae 2023; Dadykin et al. 2023, 2024a). In our material, I. raridentatus was found in the inshore biotopes of a natural lake, a sand quarry and two reservoirs. In qualitative samples from the open and plant-filled littoral of a small reservoir (Nos. 25, 26; see Appendix 1), on silt-clay sand, it was especially numerous.

Remarks. According to the latest revision ( Dadykin et al. 2024a), some previously published finds of I. cf. sarsi Stingelin, 1913 and I. sordidus (Liévin, 1848) from East Asia might obviously also be attributed to I. raridentatus , but the results need additional verification, preferably by molecular methods.