Three new species of Sectonema Thorne, 1930 (Dorylaimida: Aporcelaimidae) from Vietnam

Abstract

Three new species of the genus Sectonema collected from natural habitats in Vietnam are studied, described and illustrated, including line drawings, LM and/or SEM pictures. Sectonema birrucephalum sp. n. is characterised by its 2.73-4.35 mm long body, lip region 18-20 mu m broad and offset by deep constriction, odontostyle 10.0-11.5 mu m long on its ventral side, 659-989 mu m long neck, pharyngeal expansion occupying 63-68% of total neck length, uterus a simple tube, 221-277 mu m long, pars refringens vaginae present, V = 54-56, tail short (31-43 mu m, c = 85-111, c' = 0.6-0.8) and rounded, spicules 72-75 mu m long, and four or five irregularly spaced ventromedian supplements beyond the range of the spicules. Sectonema buccociliatum sp. n. is distinguished by its 2.00-2.46 mm long body, lip region offset by constriction, 19-20 mu m broad and bearing perioral cilia-like structures, odontostyle 13-14 mu m long at its ventral side, 530-625 mu m long neck, pharyngeal expansion occupying 62-69% of total neck length, uterus a simple tube, 116152 mu m long, pars refringens vaginae present, V = 56-62, tail short (23-31 mu m, c = 72-104, c' = 0.6-0.8) and rounded, spicules 56-68 mu m long, and 3-5 spaced and weakly developed ventromedian supplements beyond the range of the spicules. Sectonema ciliatum sp. n. is characterised by its 2.79-3.13 mm long body, lip region offset by constriction, 21-22 mu m broad and bearing perioral cilia-like structures, odontostyle 14-15 mu m long at its ventral side, 699-722 mu m long neck, pharyngeal expansion occupying 60% of total neck length, uterus a simple tube, 201-244 mu m long, pars refringens vaginae present, V = 52-53, tail short (33-35 mu m, c = 82-92, c' = 0.6-0.7) and rounded, spicules 70-72 mu m long, and three or four spaced and weakly developed ventromedian supplements beyond the range of the spicules. Molecular data obtained for S. ciliatum sp. n. and the derived evolutionary tree show a close phylogenetic relationship with other species of the genus.