Two new species of free-living nematodes (Nematoda) from Vietnam Author Tsalolikhin, S. Ya. text Zoosystematica Rossica 2020 Zoosyst. Rossica 2020-03-31 29 1 11 16 http://dx.doi.org/10.31610/zsr/2020.29.1.11 journal article 57167 10.31610/zsr/2020.29.1.11 e387fc4b-0c64-494e-a2ad-d3b07f69e985 2410-0226 10124222 urn:lsid:zoobank.org:pub:0BAEA1B3-2FE7-427E-A6BA-718F5800CFDB Monhystera vietnamica sp. nov. ( Figs 1−4 ) Holotype . Female , Vietnam , Tuyn Quang Prov . , Na Hang Distr. , Tung Vui Commune , pond in forest, 400 m a.s.l. , 22°19′46″N , 105°25′47″E , 16 June 2019 , coll. L. Iogansen. Microscope slide No. A-9238 , ZISP . Paratypes . 9 females , same data as for holotype . Description. Females. Morphometric description of the holotype and paratypes is given in Table 1 . Cuticle thin, about 1 µm. Space between internal organs with small cristalloid bodies of various sizes. Head not offset from body outline. Labial papillae undetectable. Diameter of amphidial fovea corresponding to 30% of body width. Ocellus present at about 20–26 (23) µm from anterior end. Cheilostome medium-sized, with thin walls. Esophagus muscular, gradually dilating towards its base. Cardium mushroom-shaped. Renette more or less oval, located somewhat below cardium; canal of renette and excretory pore not visible. Reproductive system monodelphic, prodelphic. Oocytes arranged in several rows in germinal zone. Uterus usually containing one or two eggs : 29–36 x 14–23 µm. Vagina very long, cuticularised, noticeably longer than one vulval body diameter. Paravulval gland present. Rectum longer than anal diameter. Tail slender, filiform. Male not found. Comparision . The new species Monhystera vietnamica sp. nov. most closely resembles M. uncigubernaculum Zeidan, Jacobs et Geraert, 1989 , which was described from Africa (Zeidan, Jacobs & Geraert, 1989), and M. rolandi Khan et Tahseen, 2006 from India (Khan & Tahseen, 2005). The main differences of the new species from M. uncigubernaculum are the following: vagina 45–52 µm ( vs 25–37 µm), rectum/anal body diameter 0.9 ( vs 0.7), and tail filiform ( vs tail with slightly swollen spinneret). The main differences of the new species from M. rolandi are: ocellus present ( vs absence of ocellus), cephalic setae 5 µm ( vs 3–4 µm), and tail filiform ( vs tail gradually tapering). Etymology . This species name is a Latinized toponym.