Two free-living nematode species found the interstitial zone of the splash zone of Lake Baikal have been described. Eumonhystera arenosa sp. n. is similar to E. filiformis (Bastian, 1865) Andrássy, 1981, but it has longer body and spicules, a bulb-shaped expansion of pharynx, and shorter inner labial sensillae; it is also
characterized by a different ratio between the tail length and the distance from vulva to anus. Tripyla affinis de Man, 1880 found in the water bodies of the Far East has been assigned to the new species T. alekseevi sp. n., since there are differences between these two closely related species. Tripyla alekseevi sp. n. is close morphologically
to T. affinis de Man, 1880, but differs by longer inner labial sensillae, a narrower labial region, a smaller number of supplements in males, and a longer gubernaculum. A key for the five valid species of the genus Tripyla inhabiting Lake Baikal is given.