Needle nematodes have an economic importance by causing damage to a wide range of natural and cultivated plants not only by directly feeding on root cells, but also by transmitting plant nepoviruses. Two new Longidorus nematodes, Longidorus oakcrassus n. sp. and Longidorus oakgracilis n. sp., are described and illustrated from populations associated with the rhizosphere of Pyrenean oak (Quercus pyrenaica Wild.) in southern Spain. The taxonomic position of both new species within the genus was assigned using an integrative approach. Morphologically, L. oakcrassus n. sp. is characterized by a female with a large and robust body size (9.2–12.2 mm), lip region anteriorly flattened to slightly rounded and almost continuous or slightly offset by a depression with body contour, ca 25.5–32.0 μm wide, amphidial fovea with slightly asymmetrical lobes, stylet composed by an odontostyle moderately long (110.0–133.5 μm) and odontophore weakly developed, pharynx short ending in a terminal pharyngeal bulb with common arrangement of pharyngeal glands, tail short almost hemispherical shape. Longidorus oakgracilis n. sp. is characterized by having a moderately long and thin female body (5.4–7.9 mm in length), a bluntly-rounded lip region, set off from body contour by a slight depression, amphidial fovea funnel-shaped without lobe, odontostyle moderately long (94.0–106.0 μm), pharyngeal bulb with common arrangement of pharyngeal glands, short tail, bluntly hemispherical. The presence of males is common in both species. Integrative diagnosis was based on molecular data using D2-D3 expansion domains of the 28S rRNA, 18S rRNA, ITS1 rRNA and partial coxI gene sequences and morphology. Although different gene markers show variations in the phylogenetic relationships, phylogeny indicated that L. oakcrassus n. sp. is phylogenetically related with several species described from the Iberian Peninsula, including L. oakgracilis n. sp., which is clustered with L.cf. olegi, L. lusitanicus and L. silvestris.

This research was financially supported by grant 201740E042, “Análisis de diversidad molecular, barcoding, y relaciones filogenéticas de nematodos fitoparásitos en cultivos mediterráneos” from Spanish National Research Council (CSIC). Authors thank G. León Ropero and J. Martín Barbarroja (IAS-CSIC) for the excellent technical assistance. The first author acknowledges the China Scholarship Council (CSC) for financial support. The second author is a recipient of Humboldt Research Fellowship for Postdoctoral Researchers at Helmholtz Centre for Environmental Research-UFZ, Leipzig, Germany. The fourth author acknowledges Spanish Ministry of Economy and Competitiveness for the “Ramon y Cajal” Fellowship RYC-2017-22228.