Nygolaimidae Thorne, 1935

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 : 17-18

Family Nygolaimidae Thorne, 1935

28. Nygolaimidae gen. spp.— {8, 54, 63, 64} (5, 4, 0, 18; 6)

Population structure and abundance. Single juvenile or female from undetermined genera at each biotope.

29. * Aquatides aquaticus (Thorne, 1930) Thorne, 1974 — {51} (0, 4, 0, 0; 1)

Population structure and abundance. One juvenile specimen and two females (~1 x10 3 /m2). Ecology and distribution. Amphibiont. Prefers water bodies but may occur in wet soil. Widely distributed in European countries, registered in Asia ( India, Bangladesh) and North America ( Canada, USA) ( Peña-Santiago 2006; Andrássy 2009b). This is the first record for Vietnam.

30. ** Aquatides heynsi Gusakov & Gagarin, 2015 — {3, 16, 40, 53, 56} (5, 1, 8, 0; 7)

Population structure and abundance. At most sites—a single female or male, at site 16—four females (more than 1 x10 3 /m2).

Ecology and distribution. Ecology presumably similar to previously described species. Found in both large and small (possibly ephemeral) water bodies. New species ( Gusakov & Gagarin 2015c). Besides Vietnam, also recovered from soil habitat in Pakistan but probably spread wider since it may be mixed with other close species (see Remarks).

Remarks. The first findings of representatives of this new species we attributed to A. intermedius (de Man, 1880) Heyns, 1968 (Gusakov et al. 2014). Additional specimens from Vietnamese water bodies differ both from A. intermedius and from another close species, A. thornei (Schneider, 1937) Heyns, 1968 when assessed by a series of morphometric parameters. This was the reason we attributed these specimens to a new species ( Gusakov & Gagarin 2015c). A population of A. thornei found in soil from Pakistan, and having similar characteristics, was attributed to this species ( Heyns 1968; Gusakov & Gagarin, 2015c). It is possible that A. heynsi occurs in other regions where the morphologically similar species, A. intermedius and A. thornei , have been reported and with which it may be mixed.

31. Aquatides thornei (Schneider, 1937) Heyns, 1968 — {55, 59, 68} (0, 0, 15, 9; 4)

Population structure and abundance. At the first site—10 juveniles and eight females (7 x10 3 /m2), at the other two—eight and four specimens (juvenile individuals and females in equal proportions), respectively (1– 3 x10 3 /m2).

Ecology and distribution. Amphibiont. Occurs both in water bodies and in soil. Recorded from South Africa, Sumatra, and the Galapagos Archipelago; relatively widespread in Asian region ( Heyns 1968; De Ley & Coomans 1995; Peña-Santiago 2006). Repeatedly noted in Vietnamese water bodies ( Gagarin & Nguyen 2005a; Nguyen & Nguyen 2005; Gagarin & Nguyen 2008a, b).

32. * Laevides laevis (Thorne, 1939)Thorne, 1974 — {50, 52, 53} (0, 11, 0, 0; 4)

Population structure and abundance. At site 52—one male, at sites 50 and 53, respectively—three juveniles, four females, three males (~4 x10 3 /m2) and 19 juveniles, four females, four males (10 x10 3 /m2). Ecology and distribution. Amphibiont. Dwells in terrestrial and aquatic habitats. Cosmopolitan ( Heyns 1968; Gagarin 1992). Not previously registered in Vietnam.