Actinolaimidae Thorne, 1939

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 : 23-24

Family Actinolaimidae Thorne, 1939

61. Neoactinolaimus Thorne, 1967 sp.— {70} (0, 0, 0, 9; 1)

Population structure and abundance. One juvenile specimen.

Remarks. Most likely, this immature specimen does not belong to the species N. tenuis Gagarin & Gusakov, 2013 , described below, since it already has a longer odontostyle and tail at this developmental stage. We have found no reports of other species of the genus Neoactinolaimus in Vietnam.

62. ** Neoactinolaimus tenuis Gagarin & Gusakov, 2013 — {8, 45, 46, 51, 52, 56} (5, 14, 8, 0; 8)

Population structure and abundance. At site 8—numerous (37) juveniles, five females, 18 gravid females and 31 males (34 x10 3 /m2). At sites 51 and 52—6 to 10 juveniles, 3 to 5 males and single female with eggs (3– 6 x10 3 /m2), at site 56—single juvenile specimen and gravid female, while in the qualitative samples (45 and 46)— 40 to 80specimens of all stages and sexes.

Ecology and distribution. Like other representatives of this genus, most likely a hydrobiont ( Gagarin 2001; Andrássy 2009b). New species. Found and described in the littoral area of a relatively large reservoir ( Gagarin & Gusakov 2013c). Later on was found in small, shallow water bodies as well.

63. ** Paractinolaimoides camranhius Gagarin & Gusakov, 2013 — {3, 5, 23, 26–29, 31, 36, 37} (16, 18, 15, 0; 14)

Population structure and abundance. Maximum abundance was recorded in sample 31—19 juveniles, eight females, six gravid females and 21 males (20 x10 3 /m2). In the rest of the quantitative samples—1 to 17 specimens of different stages and sexes (up to 6 x10 3 /m2), in qualitative samples 28 and 29—5 to 14 specimens of different stages and sexes.

Ecology and distribution. Presumably a hydrobiont. To date found only in permanent, mostly large, water bodies: lakes, reservoirs and quarries. New species ( Gagarin & Gusakov 2013c).

64. ** Paractinolaimus cattienus Gusakov & Gagarin, 2015 — {65, 70} (0, 0, 0, 18; 3) Population structure and abundance. At site 65—nine juveniles and a single female (4 x10 3 /m2), at site 70— two females (one gravid) and one male (~1 x10 3 /m2).

Ecology and distribution. Likely an amphibiont. Found only in small forest brooks. New species (Gusakov & Gagarin 2015b).

65. * Trachypleurosum Andrássy, 1959 sp.— {6} (5, 0, 0, 0; 1)

Population structure and abundance. One male.

Ecology and distribution. Likely an edaphobiont, accidentally fallen into this body of water. Representatives of this scarce, rare genus occur in wet soil and mosses ( Khan et al. 1991; Andrássy & Esquivel 2012). Not previously recorded from Vietnam.

Remarks. The lack of females prevented reliable identification of this representative of the genus. Based on main morphometric features, the male found in Vietnam is closest to T. conforme (Schneider, 1935) Andrássy 1959 , registered in West Africa and to T. venezolanum Coomans, Vinciguerra & Loof, 1990 , found in Central and South America ( Andrássy & Esquivel 2012), but differs from both species in some features. It also differs to an even higher extent from T. indicum Khan, Ahmad & Rahaman, 1991 and T. karnatakum Khan & Jairajpuri, 1994 , both known from India ( Andrássy & Esquivel 2012).