Tatyana V. Naumova

Two new species of Theristus Bastian, 1865 (Nematoda: Xyalidae) from the interstitial zone of Lake Baikal, Siberia, Russia

Theristus tsalolikhini sp. n. and T. psammophilus sp. n. from the interstitial zone of Lake Baikal, Russia, are described from numerous females and males. Theristus tsalolikhini sp. n. is similar to T. ruffoi, but differs from it by the presence of elongate spermatheca, narrower labial region, shorter outer labial setae, larger amphidial fovea, more anterior position of amphidial fovea and shorter spicules and gubernaculum. Theristus psammophilus sp. n. is similar to T. athesinus, but differs from it by the presence of an elongate spermatheca, shorter outer labial setae, more anterior position of the amphidial fovea and longer spicules and gubernaculum. A pictorial key is provided for males of freshwater and groundwater species of Theristus.

Prodorylaimus baikalensis sp. n. and Mononchus minutus sp. n. (Nematoda) from Lake Baikal, Russia

Two new nematode species found in Lake Baikal (Russia) are described and illustrated. Prodorylaimus baikalensis sp. n. is morphologically close to P. irminii Vinciguerra Orselli, 2011 and P. obesus Ahmad Jarajpuri, 1982. From the first species it differs by the shorter and thinner body, longer tail, longer odontostyle and greater number of ventromedian supplements. From the second species it differs by the longer and more slender tail, shorter odontophore, longer female prerectum and greater number of ventromedian supplements in males. Mononchus minutus sp. n. is similar to M. niddensis Skwarra, 1921 and M. agilis Gagarin Mataphonov, 2004. The new species differs from M. niddensis by the shorter body, more slender tail, longer buccal cavity, longer spicules and smaller number of ventromedian supplements in males. From M. agilis it differs by the shorter and thinner body, shorter tail, longer spicules and smaller number of ventromedian supplements in males.

Ethmolaimus riparius sp. n. and Paramononchus major sp. n. (Nematoda) from Lake Baikal, Russia

Two new nematode species found in Lake Baikal (Russia) are described and illustrated. Ethmolaimus riparius sp. n. is morphologically close to E. pilosus Shoshin, 1998 and E. lanatus Shoshin, 1998. The new species differs from E. pilosus by the longer and thinner body (L = 1228-1501 µm, a = 26-34 vs L = 720-1070 µm, a = 19-23), larger stoma (26-32 µm long vs 19-24 µm long), longer spicules and gubernaculum (45-50 µm long and 21-25 µm long vs accordingly 32-37 µm long and 8 µm long). E. riparius sp. n. differs from E. lanatus by the longer body (L = 1228-1501 µm vs L = 680-1180), shorter cephalic setae (its length is equal 1.1-1.4 labial region diameter vs 1.6-2.1 labial region diameter) and longer spicules and gubernaculum (45-50 µm long and 21-25 µm long vs accordingly 25-30 µm long and 7-8 µm long). Paramononchus major sp. n is close to P. orientalis Gagarin & Naumova, 2012, but differs from it by the longer body (L = 5926-7820 µm vs L = 3081-3778 µm), longer spicules (410-475 µm long vs 208-238 µm long) and larger number of precloacal supplements (52-61 vs 21-24). Keys for the identification of valid species of the genera Ethmolaimus and Paramononchus are given.

Domorganus gigas sp. n. (Nematoda) from Lake Baikal, Russia

The genus Domorganus Goodey, 1947 includes nine valid species found in marine, freshwater and terrestrial habitats in Europe and Asia (Holovachov 2012). One species, D. acutus (Tsalolikhin, 1977) Lorenzen, 1981, is found in Lake Baikal, inhabiting the littoral zone (3 m depth) (Gagarin & Naumova, 2011).

EUTOBRILUS OBESUS SP. NOV. AND E. BRZESKII SP. NOV. (NEMATODA: TRIPLONCHIDA: TOBRILIDAE) FROM LAKE BAIKAL, RUSSIA

Abstract. Eutobrilus obesus sp. nov. and E. brzeskii sp. nov. are described and illustrated based on the material collected from Lake Baikal, Siberia, Russia.