Paramononchus orientalis sp. n. and Ethmolaimus maximus sp. n. (Nematoda) from Lake Baikal, Russia

Abstract

Two nematode species found in Lake Baikal, Russia are described. Paramononchus orientalis sp. n is morphologicallyclose to P. arcticus Mulvey, 1978, but differs from it in the shorter body (L = 3.08–3.78 mm vs L = 3.5–4.0 mm), largerbuccal cavity (64–68 x 30–32 µm vs 44–48 x 19–21 µm), larger eggs (140–155 x 80–87 µm vs 105–110 x 60–80 µm), lessslender tail in females (c’ = 4.2–5.0 vs c’ = 5.7–6.5), longer spicules (208–238 µm long vs 70 µm long) and shape ofgubernaculum. A key for the identification of valid species of the genus Paramononchus is given. Ethmolaimus maximussp. n. is the largest species yet described in the genus Ethmolaimus. It differs from E. pratensis de Man, 1880 in the longerbody (L = 1.65–2.09 mm vs L = 0.6–1.2 mm), comparatively shorter pharynx (b = 8.0–9.6 vs b = 4.8–7.0), comparativelylonger cephalic setae (45–55 % of labial region diameter vs 30–35 % of labial region diameter) and longer spicules (52–56µm long vs 38–48 µm long). Ethmolaimus intermedius Jensen, 1994 is synonymized with Ethmolaimus pratensis de Man, 1880.