Ilyocryptus spinifer Herrick, 1882

7. Ilyocryptus spinifer Herrick, 1882 View in CoL

Localities and specimens found: 8 − 15♀, 9♀ ov, 3♀ em; 15 − 1♀, 1♀ em; 32 − 4♀, 1♀ ov, 7j; 45 − 1♀; 46 − 1♀; 49 − 3♀, 3♀ ov; 50 − 3♀, 1j; 51 − 2♀ em, 1j; 60 −1j; 65 − 2♀ ov, 3j.

Distribution and ecology. Ilyocryptus spinifer is one the most common and well known members of the genus, especially in the tropics and subtropics worldwide. It is nearly cosmopolitan, only absent in the northern Palaearctic regions and Antarctica ( Kotov & Dumont 2000; Kotov & Štifter 2006; Kotov et al. 2013a; Korovchinsky et al. 2021b; Dadykin et al. 2024b). This ilyocryptid had been recorded frequently in the majority of countries within the Oriental area, including under the synonymized names: I. halyi Brady, 1886 , I. longiremis Sars, 1888 , I. verrucosus Daday, 1905 , or as I. cf. spinifer specimens ( Fernando 1974, 1980; Idris & Fernando 1981; Rajapaksa & Fernando 1982a; Idris 1983; Michael & Sharma 1988; Sanoamuang, 1998; Rane 2002, 2005, 2011; Maiphae et al. 2005, 2008; Tanaka & Ohtaka 2010; Korovchinsky 2013; Van Damme et al. 2013; Padhye & Dumont 2015; Sinev & Yusoff 2015, 2018; Sinev et al. 2015, 2020; Xiang et al. 2015; Lopez et al. 2017; Sharma & Sharma 2017; Gogoi et al. 2018; Tiang-nga et al. 2020; Choedchim & Maiphae 2023; Kotov et al. 2024). In Vietnam, this cladoceran was noted (at first as I. halyi , later as I. spinifer ) in various types of water bodies throughout the country, from plains to mountains, in both benthic and planktonic samples ( Dang et al. 1980, 2002; Dang & Ho 2001; Duong et al. 2008; Sinev & Korovchinsky 2013; Gusakov et al. 2014; Zhdanova 2014; Phan et al. 2015; present study).

Ilyocryptus spinifer occurs in almost all types of freshwater bodies and in a wide range of physical and chemical conditions. This ilyocryptid can also be found in saline estuaries. It is a typical benthic crustacean, spending most of its life in the upper layer of bottom sediments (mainly silty and clay). However, the species is not devoid of the ability to swim and therefore can sometimes be encountered in plankton, as well as among thickets of aquatic vegetation ( Paranaguá et al. 2005; Kotov & Štifter 2006; Sinev & Korovchinsky 2013; Korovchinsky et al. 2021b). In our material, I. spinifer was the most common representative among all registered Cladocera , although not very numerous.

Remarks. Despite the fact that the last worldwide revision showed no differences between I. spinifer populations from different continents ( Kotov & Dumont 2000), this taxon still needs further comparative studies, including using molecular methods. It is possible that, nevertheless, this is a complex of very similar relatives ( Kotov & Štifter 2006; Lopez et al. 2017; Kotov et al. 2024).