An annotated checklist of the main representatives of meiobenthos from inland water bodies of Central and Southern Vietnam. I. Roundworms (Nematoda) Author Gusakov, Vladimir A. Author Gagarin, Vladimir G. text Zootaxa 2017 4300 1 1 43 journal article 32584 10.11646/zootaxa.4300.1.1 7eb2410e-8578-432a-88f8-bc129d0a5b08 1175-5326 837117 5FA0C659-9C52-4ABB-9CB6-1FB5CDDDF9F8 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.