Heterorhabditis mexicana n. sp. (Rhabditida: Heterorhabditidae) from Tamaulipas, Mexico, and morphological studies of the bursa of Heterorhabditis spp.

Abstract A new species of nematode in the genus Heterorhabditis was found in the northern part of the state of Tamaulipas, Mexico. Morphological and molecular data indicate that this nematode is a new species. The new species is described as Heterorhabditis mexicana n. sp. and is a sister taxon to H. indica. Heterorhabditis mexicana n. sp. is morphologically similar to H. bacteriophora, H. brevicaudis and H. indica and can be distinguished from these species mainly by male and female characters. Of the examined specimens of H. mexicana n. sp., 70% of males have eight pairs of bursal papillae, compared to nine in all other species. The ratio of the gubernaculum to spicule length (GS ratio) is higher than that of H. bacteriophora, H. brevicaudis and H. indica and the length of the spicule relative to anal body width (SW) is lower than all other species. For females, the vulval form of the new species is quite different from that of those species with a similar morphology (i. e ., H. bacteriophora and H. indica) and more closely resembles that of H. zealandica. The new species can also be distinguished from H. megidis, H. zealandica and H. marelatus by the body length, pharynx length of the infective juvenile and D% (distance from anterior end/pharynx length × 100), GS and SW ratios of males. In the ITS region of the rDNA tandem repeating unit, H. mexicana n. sp. has evolved 13 autapomorphic nucleotide character states, differing from its sister taxon H. indica at 113 aligned positions. The morphological and molecular data are sufficient to identify cladogenesis and delimit H. mexicana n. sp. as evolving independently from the other members of the genus.