Characterization of a new spiral nematode, Helicotylenchus asiaticus n. sp., and three known species from Korea; with comments on the validity of Helicotylenchus microlobus Perry in Perry, Darling & Thorne, 1959

A new spiral nematode Helicotylenchus asiaticus n. sp., recovered from sandy rhizosphere of Poa pratensis from Korea, is characterized based on integrative taxonomy, considering both morphological and molecular phylogenetic inferences from analyses of the 28S-rRNA and ITS-rRNA gene sequences. Additionally, H. caudatus is characterized for the first time outside its type locality; notes on the taxonomic status of H. microlobus are stated, and the existence of H. dihystera in Korea is molecularly confirmed. The new species is characterized by a lip region not offset; hemispherical, bearing 4–5 annuli; stylet knobs sloping posteriorly, rarely anteriorly flattened; spermatheca, offset and filled with sperms; incisures of the lateral field areolated in pharyngeal region, with incomplete areolation in the tail region; inner incisures usually distally modified into a u-shape or y-shaped configuration; phasmids postanal, situated at 3–8 annuli posterior to anus level; tail conical, bearing 8–15 annuli, ending in a rounded to pointed extremity; and males abundant. The new species is morphologically similar to H. erythrinae, H. californicus, H. electropicus, H. tropicus, H. conicus, H. elegans, H. interrogativus, H. saxeus, H. certus and H. silvaticus but differs from all, either by lip region shape, stylet knob shape, sperm filled spermatheca, phasmid position, tail termini shape and (or) presence of males. Sequence data analyses from amplified regions suggest that Helicotylenchus asiaticus n. sp. is a sister species to unidentified Helicotylenchus sp. From Korea.