Mydonomidae Thorne, 1964

Gusakov, Vladimir A. & Gagarin, Vladimir G., 2017, An annotated checklist of the main representatives of meiobenthos from inland water bodies of Central and Southern Vietnam. I. Roundworms (Nematoda), Zootaxa 4300 (1), pp. 1-43 : 16-17

Family Mydonomidae Thorne, 1964

22. * Calolaimus Timm, 1964 sp.— {50–55, 59, 62, 63, 67, 68} (0, 18, 15, 36; 15)

Population structure and abundance. A relatively abundant species. The maximum number of individuals (87 juveniles and 13 females) was found at site 50 (total abundance 37 x10 3 /m2); at sites 53–55—15–23 juvenile specimens and 5 to 14 females (7–13 x10 3 /m2), at the remaining habitats—1 to 7 juveniles and females (up to 3 x10 3 / m2).

Ecology and distribution. Most likely an amphibiont since it was found exclusively in shallow floodplain and forest water bodies, including those periodically drying out. The representatives of this genus parasitize plant root systems, including hydrophytes ( Gagarin 2001). Four out of seven species have been reported in water bodies and rice fields in Europe and Asia ( Peña-Santiago 2006; Andrássy 2009b). No previous reports on any species of the genus Calolaimus from Vietnam were found.

Remarks. This species is one of the most widespread and numerous nematodes in the bottom meiofauna of studied water bodies of various types in the Cát Tiên National Park (Đỗng Nai Province). However , we failed to definitively identify it owing to the lack of males in the samples. As identified by females according to the key in Ahmad & Jairajpuri (1983), this species is close to C. ditlevseni (Micoletzky, 1922) Timm, 1964 , C. papillatus Timm, 1964 and C. parapapillatus Dhanachand & Jairajpuri, 1980 . All three species were found in Asia : the first, in Indonesia (Java Island) ; the second, in eastern Pakistan; the third, in India (Timm 1 964; Peña-Santiago 2006).

23. ** Dorylaimoides curvicaudatus Gagarin & Gusakov, 2015 — {69} (0, 0, 0, 9; 1)

Population structure and abundance. Two females and three males (2 x10 3 /m2).

Ecology and distribution. Amphibiont or terrestrial species accidentally fallen into aquatic environments (edaphobiont), like the vast majority of representatives of this genus ( Peña-Santiago 2006). New species with only one habitat known to date (Gagarin & Gusakov 2015b).

24. * Dorylaimoides teres Thorne & Swanger, 1936 — {50} (0, 4, 0, 0; 1)

Population structure and abundance. 27 females (10 x10 3 /m2).

Ecology and distribution. Dwells predominantly in soil but also found in aquatic habitats indicating, together with our finding, that this is a potential amphibiont. Recorded in some European countries, North America (USA) and Asia ( Mongolia) ( Peña-Santiago 2006; Andrássy 2009b). Had not been registered in Vietnam previously.

Remarks. There are doubts concerning conspecificity of various populations of this species. A revision of these populations is necessary ( Peralta & Peña-Santiago 1995; Peña-Santiago & Peralta 1997).

25. * Dorylaimoides thornei ( Jairajpuri, 1964) Siddiqi, 1969 — {50, 51, 55} (0, 7, 8, 0; 4)

Population structure and abundance. 3 to 5 juvenile individuals and females at the first and last sites and only a single male at site 51 (1–2 x10 3 /m2).

Ecology and distribution. As for the two previous species, either edaphobiont or amphibiont. Rare representative of the genus. Described from soil in India and, apparently has not been reported in other regions and habitats until the present finding in Vietnam ( Jairajpuri 1964; Peña-Santiago & Peralta 1997).

26. ** Dorylaimoides vietnamicus Gagarin & Gusakov, 2015 — {50, 59, 66} (0, 4, 8, 9; 4) Population structure and abundance. In total three females at the first two sites and one male at site 66 (up to 1 x10 3 /m2).

Ecology and distribution. Ecology presumably similar to previously mentioned species of the genus. New species (Gagarin & Gusakov 2015b). To date, has been found only in the noted habitats.

27. Dorylaimoides Thorne & Swanger, 1936 spp.— {22, 66} (5, 0, 0, 9; 3)

Population structure and abundance. 3 individuals (two juveniles and female) and a single female at the first and second site, respectively.

Remarks. This taxon includes at least two representatives of the genus; we failed to reliably identify them to species rank. Until recently in Vietnamese water bodies only one species of the genus Dorylaimoides has been reported: D. micoletzkyi (de Man, 1921) Thorne & Swanger, 1936 ( Nguyen & Nguyen 2005; Nguyen 2007).