Aquatic nematodes from Ethiopia .3. The genus Eumonhystera Andrassy, 1981 (Monhysteridae: Nematoda) with the description of E-geraerti n sp

Six species of the genus Eumonhystera, one of which is new to science, are described from bottom samples of Lake Tana and two associated rivers, River Abbay and R. Gelda, Ethiopia. E. geraerti n. sp. can be identified by being the only species in the genus that combines very posteriorly positioned vulva [V% = 68.2 +/- 0.7 (67.3-69.3)] with very anteriorly positioned amphids (Amph-ABE/LRW = 0.8). The other five species encountered, E. dispar (Bastian, 1865) Andrassy, 1981, E. filiformis (Bastian, 1865) Andrassy, 1981, E. pseudobulbosa (von Daday, 1896) Andrassy, 1981, E. mwerazii (Meyl, 1957) Andrassy, 1981, and E. vulgaris (de Man, 1880), Andrassy, 1981, are described in detail. The identities of some of the already described populations of E. dispar, E. filiformis and E. vulgaris are questioned and clearer and better ways of defining each of these three species are suggested. A peritrophic-like membrane on the outer side of the brush-border of the intestine of E. mwerazii, a species reported here for the first time out of its type locality, is reported. Also, scanning electronmicrographs of sectioned and entire specimens of E. mwerazii are presented. All species are reported from Ethiopia for the first time.