Sectonema caobangense sp n. from Vietnam (Nematoda, Dorylaimida, Aporcelaimidae)

Sectonema caobangense sp. n. from evergreen forest soil in Vietnam is described, including scanning electron micrograph (SEM) observations and D2-D3 LSU rDNA analysis. The new species is characterized by its 3.12 to 5.80 mm long body, lip region offset by deep constriction and 21 to 23 mu m broad, mural tooth 13 to 14 mu m long at its ventral side, 940 to 1,112 mu m long neck, pharyngeal expansion occupying 61% to 69% of total neck length, uterus a long simple tube-like structure 292 to 363 mu m long or 2.7 to 2.9 times the corresponding body diameter, pars refringens vaginae well developed, V = 48 to 56, short (36-51 mu m, c = 77-132, c' = 0.5-0.8) and rounded tail, 87 to 99 mu m long spicules, and four or five irregularly spaced ventromedian supplements bearing hiatus. Sectonema caobangense sp. n. differs from the typical pattern of Sectonema in the nature of the stomatal protrusible structure, bearing a mural tooth attached to the ventral side of the stoma. Molecular data obtained and the derived evolutionary trees support a close phylogenetic relationship with other Sectonema species.