Abstract
A new species of the genus Metaxonchium is described from natural habitats in Iran. The new species is characterized by having body length of 2.46–3.12 mm, lip region offset by constriction and 8–11 µm wide, odontostyle fusiform and 10–12 µm long, neck 773–1150 µm long, anterior portion of pharynx bearing a spindle-shaped thickening with valve-like structures inside, both parts of the pharynx separated by a short isthmus-like narrowing, pharyngeal expansion 531–825 µm long and occupying up to three-fourths of total neck length, female genital system monodelphic-opisthodelphic, anterior genital branch reduced to a large uterine sac and a small terminal mass, posterior uterus long and tripartite with an intermediate region bearing apophyses, V = 53–57, caudal region conoid with broadly rounded terminus (24–35 µm, c = 79–105, c’ = 0.6–0.9), spicules 92–103 µm long and 7–10 spaced ventromedian supplements, at least two of them within the range of spicules. The taxonomy of the genus Metaxonchium is updated, including a list of its species, a key to their identification and a compendium of their morphometrics. Four species are transferred from Axonchium to Metaxonchium: M. coxi, M. japonicum, M. mizukuboi and M. zealandicum.