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

Abstract

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.