Daptonema brzeskii sp. n. and D. rivale sp. n. (Nematoda, Monhysterida, Xyalidae) from Mekong River Mouth, Vietnam

Two new nematode species of the genus Daptonema, D. brzeskii sp. n. and D. rivale sp. n., are described and illustrated based on the material collected from Mekong River Delta, Vietnam. Daptonema brzeskii sp. n. is close to D. lutosum Gagarin, 2021, D. dihystera Gagarin, Nguyen Vu Thanh, 2005 and D. hyalocella Aryuthaka, Kito, 2012 in the presence of postvulval uterus sac, and it is close to D. paraoxyuroides Nguyen Dinh Tu, Gagarin, Nguyen Vu Thanh, Nguyen Thi Xuan Phuong, Nguyen Thanh Hien, 2014 in the shape of spicular apparatus. From the former species it differs in the thinner body, slenderer tail, narrower labial region, shorter outer labial setae and spicules, larger pharyngostoma, and vulva located farther from the anterior body end. It differs from D. dihystera in the shorter body, narrowed labial region, shorter outer labial setae and spicules, and larger pharyngostoma. Daptonema brzeskii sp. n. differs from D. hyalocella in the thinner body, amphidial fovea located closer to the anterior body end, shorter outer labial setae, longer spicules, presence of gubernaculum, larger pharyngostoma, and vulva located farther from the anterior body end. From D. paraoxyuroides, D. brzeskii sp. n. differs in the presence of postvulval sac, longer body, slenderer tail, shorter outer labial setae and gubernaculum. Daptonema rivale sp. n. is similar to D. setihyalocella Aryuthaka, Kito, 2012 in shape of spicular apparatus and to D. brzeskii sp. n. in the shape of pharyngostoma. Daptonema rivale sp. n. differs from D. setihyalocella in the shorter and comparatively thinner body, shorter outer labial setae, spicules, and gubernaculum, bigger pharyngostoma, and vulva located farther from the anterior body end. Daptonema rivale sp. n. differs from D. brzeskii sp. n. in the longer body and outer labial setae, less slender tail, and vulva located farther from anterior body end.