Unveiling Hidden Diversity: A New Laimaphelenchus Species from Elm Bark in Northern Iran

This study aimed to investigate the diversity of nematodes exhibiting various feeding strategies—including fungivorous, bacterivorous, predatory, and insect-associated forms—particularly those linked with bark beetles and Dutch elm disease. Between 2021 and 2023, eighty samples of dried elm bark and associated beetles were collected from Golestan Forest Park, Iran. Nematodes were extracted, fixed, and mounted on permanent microscope slides for morphological examination. Identification was based on morphological and morphometric analyses using standard keys, original species descriptions, and, where needed, molecular data. Fourteen species from ten genera belonging to the superfamilies Aphelenchoidea and Sphaerularioidea were identified. Among them, one population of Laimaphelenchus sp. exhibited a unique combination of morphological characters not found in any previously described species and is therefore proposed as a new species. Key diagnostic features include a body length of 336–446 μm, stylet length of 7–8.5 μm, three lateral lines, an elongated rectangular spermatheca containing sperm, absence of a vulval flap, and a posterior uterine sac measuring 3–4 times the vulval body width. The semi-cylindrical tail terminates in a flat disc with a stalk-like extension bearing four branched tubercles, each ending in a saucer-like structure with fringed, finger-like appendages. Males are present and possess spicules with a short, straight condylus and a blunt-tipped conical rostrum. The combination of these features places the species near L. patulus, L. australis, L. phloesini, and L. vescus, but distinct morphological differences support its recognition as a novel taxon within the genus Laimaphelenchus.