Two new species of the genus Metaxonchium Coomans & Nair 1975 (Nematoda, Dorylaimida, Belondiridae) from Costa Rica, with new insights in the phylogeny of the family Belondiridae

Two new species of the genus Metaxonchium are described from natural habitats in Costa Rica. Metaxonchium parvisaccatum sp. n. is characterized by its 1.62–1.71 mm long body, lip region offset by constriction and 8.5–10 μm broad, odontostyle 10–11 μm long, neck 632–674 μm long, pharyngeal expansion occupying 68–71% of neck length, anterior genital branch reduced to a short uterine sac, 22–27 μm long or 1–2% of body length, posterior uterus long and tripartite without apophyses, vulva transverse (V = 54–55), caudal region short and rounded (23–26 μm, c = 62–76, c’ = 0.7–0.8), and male absent. Metaxonchium stenospiculum sp. n. is characterized by its 2.15–2.85 mm long body, lip region offset by constriction and 12.5–16 μm broad, odontostyle 13.5–16 μm long, neck 756–1011 μm long, pharyngeal expansion occupying 64–74% of neck length, anterior genital branch 8–13% of body length and consisting of a long uterine sac plus a terminal mass, posterior uterus long and tripartite without apophyses, vulva transverse (V = 53–59), caudal region short and rounded, nearly hemispheroid (20–28 μm, c = 91–126, c’ = 0.4–0.6) in females, and more conoid (29–41 μm, c = 80–88, c’ = 0.6–0.8) in males, spicules 96–102 μm long, and 11–14 spaced ventromedian supplements without hiatus. Molecular analysis of M. stenospiculum sp. n. D2-D3 LSU provides new insights in the phylogeny of Belondiridae as its rounded-tailed genera might constitute a monophyletic group.