Description of Longidorus cheni sp. n. (Nematoda, Longidoridae) from China.

Longidorus cheni sp. n ., an amphimictic species recovered from the rhizosphere of Larix principis-rupprechtii and Pyracantha fortuneana in Shanxi and Beijing, China, is described and illustrated. The taxonomic position of L. cheni sp. n. among other species within the genus was elucidated using morphometric and molecular data, and phylogenetic relationships were inferred using D2-D3 expansion domains of 28S and 18S rRNA genes by Bayesian Inference (BI) method. The new species is characterised by females with a medium body size (L = 4.9-6.6 mm), a lip region slightly expanded, broadly rounded frontally and laterally, the amphidial fovea broad and symmetrically bilobed at base, odontostyle long and slender (143-168 μm), odonthophore slightly swollen at the base, tail short bluntly conoid to rounded. Guide ring located far posterior from the oral aperture (70-93 μm). Males with two ad-cloacal pairs of supplements preceded by a row of 10-14 ventromedian supplements, with robust spicules measuring 111-126 μm along the median line. Three juvenile stages were present, tail shape of J1 elongate conoid while in J2 and J3 the tail gradually becomes bluntly rounded. Codes for identifying the new species are: A6-B3-C5-D2-E2-F3-G1-H1-I2-J2-K2. Longidorus cheni sp. n. belongs to a group of species with a guide ring at the mid-odontostyle position that have a predominantly Asiatic origin. It differs from all of them by a combination of morphological characters and unique sequences of partial 18S and D2-D3 region of 28S rRNA genes. The percentage dissimilarities in partial 18S and D2-D3 28S rRNA genes of L. cheni to the closest species ( L. litchii , L. fangi , L. jonesi and L. juglans ) were 1.5 %-1.8 % and 16.8-18.3 %, respectively.