Ilyocryptus undetermined

6. ** Ilyocryptus sp. (Figs. 2A–C) Localities and specimens found: 100 −1j; 101 − 1♀, 1j; 102 −1j. Distribution and ecology. Sporadic individuals of this unclear ilyocryptid were found in the riparian and channel zones of the freshwater section of the Co Chien Branch in the Mekong Delta (see Appendix 1). Similar forms have not been observed in Vietnam before. Remarks. As not all the details of the structure can be considered on our single found individuals, of which only one is an adult, the exact taxonomic status of these crustaceans is not yet clear. According to the main observable diagnostic features, these individuals belong to the I. sarsi species group and are close to its Asian representatives, such as I. thailandensis Kotov et Sanoamuang, 2004 and I. raridentatus (Kotov & Sanoamuang 2004b; Kotov & Štifter 2006; Dadykin et al. 2024a). However, compared to the former species (Kotov & Sanoamuang 2004b), this Vietnamise Ilyocryptus is clearly distinguished by the absence of a projection on the coxal segment of the antennae II. It differs from I. raridentatus (Dadykin et al. 2024a) by the relatively numerous (10–13 vs 5–8) preanal teeth on the postabdomen (Figs. 2A, C). In terms of the structure and armament of the postabdomen (Figs. 2A–C), our specimens are very similar to I. sarsi (Kotov & Štifter 2006). Ilyocryptus sarsi -like populations are now also known from South America, South and Central Africa, Malaysia, Japan and the Russian Far East, but in different regions they most likely represent a complex of close relatives, while I. sarsi s. str. appears to be an exclusively Neotropical taxon (Kotov et al. 2002; Kotov & Štifter 2006; Kotov & Elmoor-Loureiro 2008). Thus, the discovered “ sarsi -like” individuals from Vietnam may well belong to the still undescribed species of Ilyocryptus.