Cryptonchidae Chitwood, 1937

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 : 27

Family Cryptonchidae Chitwood, 1937

77. Cryptonchus abnormis (Allgén, 1933) Schuurmans Stekhoven, 1951 — {37, 66, 70} (0, 0, 8,18; 4) Population structure and abundance. Two juvenile individuals and five females at site 37 (~ 3x10 3/m2) and 1–2 females in the other samples.

Ecology and distribution. Amphibiont. Dwells in terrestrial and aquatic biotopes. Relatively widespread species. Recorded from North and South America , Africa, New Zealand, and in some countries of South and South-East Asia, including Vietnam ( Zullini & Peneva 2006; Nguyen 2007; Andrássy 2009b; Ahmad & Jairajpuri 2010).

78. * Cryptonchus exilis (Ditlevsen, 1911) Filipjev, 1934 — {16, 63, 64, 66, 67} (0, 4, 0, 36; 7)

Population structure and abundance. 1 to 4 juveniles and females at each site (up to 1x10 3/m2). Ecology and distribution. Ecology is similar to the species described above. Cosmopolitan. Known from all continents except for Antarctica ( Zullini & Peneva 2006). Not previously found in Vietnam.

79. * Cryptonchus Cobb, 1913 sp.— {23} (5, 0, 0, 0; 1)

Population structure and abundance. One gravid female.

Remarks. With its comparatively short tail, this female differs from the two species described above and resembles C. tristis (Cobb, 1893) Cobb, 1913 . However, the length of C. tristis females ranges from 1.8–2.4 mm ( Gagarin 1993; Ahmad & Jairajpuri 2010) while our specimen is less than 1 mm (968 µm). It differs from yet another species of the genus, C. papillatus Sukul, 1968 having similarly small body size ( Sukul 1968), by the lack of mammiform papillae on lips and by some other morphological characters. It is possible that a new representative of the genus was found but analysis of a single individual is insufficient to describe this species.