Integrative characterisation of Longidorus parasabalanicus sp. nov. (Nematoda: Longidoridae) from northern Iran, with remarks on its morphological affinity to L. sabalanicus

Abstract

A new needle nematode, Longidorus parasabalanicus sp. nov. (Nematoda: Longidoridae), was collected from the rhizosphere of Astragalus spp. in mountainous areas of northern Iran. The species is characterised by a medium-sized body (female 4.0–4.8 mm; male 4.3–5.1 mm), lip region anteriorly flattened and laterally rounded, ca 12.5–14.5 μm wide, and separated from the body by a shallow depression, amphidial fovea pocket-shaped without basal lobes, moderate odontostyle (75.0–84.0 μm) and odontophore (50.0–58.0 μm), and guiding ring located at 27–33 μm from the anterior end. The pharyngeal bulb has the common arrangement of pharyngeal glands. Females have a vulva almost equatorial (V = 50–56%), short tail rounded to bluntly conoid, 41.0–47.0 μm long (c = 89.0–113.0, c′ = 0.9–1.2), with two pairs of caudal pores and a broadly rounded terminus with distinct radial lines in the hyaline region. Males are common, with spicules 68.0–80.0 μm long and eight to ten ventromedian supplements. All four juvenile stages are present, with the first-stage juvenile having a conoid tail, dorsoventrally curved with a rounded terminus. The polytomous codes for the new species are: A23-B2-C3(2)-D3-E1-F2-G1(2)-H12-I2-J1-K6. Morphologically, L. parasabalanicus sp. nov. is most similar to L. sabalanicus , and together with L. tabrizicus and L. paratabrizicus , belongs to a closely related species complex, from which it can be distinguished by a combination of subtle but consistent morphometric characters. Molecular phylogenetic analyses based on D2–D3 expansion segments of 28S rDNA, partial 18S rDNA, ITS1, and mitochondrial COI sequences support its recognition as a distinct lineage within the genus. Phylogenetic trees recover the new species in a well-supported clade with L. sabalanicus and other closely related species from Iran and the Mediterranean. This study provides comprehensive morphological, morphometric, and molecular data for delimiting the new species and contributes to understanding Longidorus diversity in Iran and adjacent regions.