Evidence for the Synonymy of Laimaphelenchus hyrcanus with L. belgradiensis, two species of nematodes belonging to Aphelenchoididae

A population of Laimaphelenchus was isolated from the dead bark of a healthy oak tree, a site potentially favorable for fungal growth. This species is morphologically characterized by a body length of 621–796 µm, a stylet measuring 10.5–13 µm, three lateral lines, the presence of a vulval flap, and a post-uterine sac 50–78 µm long (2.2–3.6 times the vulval body width). Males exhibit a four-part tail terminus, a (2+2+2) arrangement of genital papillae, and spicules measuring 18.5–20 µm. Based on morphometric and morphological features, this population closely resembles L. hyrcanus and L. belgradiensis. However, it differs from the original description of L. belgradiensis by having a shorter stylet (10.5–13 µm vs. 13.6–15.2 µm) and a longer post-uterine sac (50–78 µm vs. 17.6–48 µm). In comparison with L. hyrcanus, the post-uterine sac is also shorter (50–78 µm vs. 97–152 µm). Previous studies on Laimaphelenchus populations from decaying oaks in Iran highlighted variability in post-uterine sac length and its potential limitations for species-level discrimination. A re-evaluation of species boundaries led to a redescription of L. belgradiensis and the proposal that L. hyrcanus may represent a junior synonym. In the present study, phylogenetic analysis based on the D2–D3 expansion segments of the LSU gene placed this population within a highly supported clade (posterior probability = 1.00), supporting the synonymy—unless additional genomic regions suggest otherwise.