Tobrilidae Filipjev 1918

Family Tobrilidae Filipjev, 1918

13. Brevitobrilus stefanskii (Micoletzky, 1925) Tsalolikhin, 1981 — {1, 2, 4–7, 9, 11–16, 18, 21, 25, 28, 29, 31, 33, 38, 51–54, 57, 58, 60, 62} (58, 46, 31, 9; 41)

Population structure and abundance. This species is one of the most abundant nematodes in the meiofauna of studied water bodies. In the majority of habitats, the population consists of all age groups and sexes; the number of specimens varies from 5–10 to 40–50; total density, from 2–3x10 3 to 17–18 x10 3 individuals per square meter. The maximal numbers (29–50 x10 3 /m2) were noted in samples 2, 31, 53, 54, and 58. At some biotopes (11, 13, 25, 33, 57, and 62) only solitary specimens were found.

Ecology and distribution. Amphibiont. Prefers water but often occurs in wet soil. Widespread in the countries of Europe and Asia, found in southern Africa (Zambia) (Tsalolikhin 1983; Zullini 2006; Andrássy 2007). Common and relatively numerous in the studied water bodies of northern Vietnam (Gagarin & Nguyen 2005a; Gagarin & Nguyen 2008a). This species is the most commonly encountered nematode in our studied water bodies, especially in the reservoirs and lakes.

Remarks. Two more species of the genus Brevitobrilus, B. graciloides (Daday, 1908) Tsalolikhin, 1981 and B. vibratus (Sukul, 1967) Tsalolikhin, 1981, have been found in Vietnamese waterbodies (Nguyen 2007). According to some researchers, B. vibratus is a synonym of B. stefanskii (Zullini 2006; Andrássy 2007). In our samples we found no specimens that could be identified (for instance, using Tsalolikhin’s (1983) key) as B. vibratus. It is worth noting that Andrássy does not separate the genera Brevitobrilus and Epitobrilus. In his monograph this species is given as E. stefanskii (Micoletzky, 1925) Andrássy 2007.

14. ** Semitobrilus andrassyi Gagarin & Gusakov, 2013 — {35} (0, 0, 8, 0; 1)

Population structure and abundance. Two juveniles and three males (~2 x10 3 /m2). Ecology and distribution. Presumably, hydrobiont similar to other representatives of this genus (Gagarin 2001). New species (Gagarin & Gusakov 2013b). Not found yet anywhere outside of the type habitat. Remarks. Was initially erroneously identified as S. closlongicaudatus (Gagarin, 1971) Tsalolikhin, 1981 (Gusakov et al. 2014).