A new species of Heligmostrongylus Travassos 1917 (Nematoda: Heligmonellidae) in small rodents (Cricetidae and Heteromyidae) from Mexico

A new species of Heligmostrongylus (Nematoda: Heligmonellidae) is described from the smallrodents Ototylomys phyllotis (Cricetidae: Tylomyinae) and Heteromys gaumeri (Heteromyidae:Heteromyinae) in the Yucatan Peninsula, Mexico, based on studies of light and scanning electronmicroscopy, and partial sequences of COI, ITS1 and 28S rRNA. Heligmostrongylus yucatanensisn. sp. is characterized by a synlophe of 13 interrupted ridges (except those forming careen) in bothsexes at midbody; males with a ventral cuticle inflation at anterior region of copulatory bursa, rays9 and 10 long, comparable in length, and rays 9 strongly curved laterally at a right angle crossingventrally rays 8; and females with a torsion of 180° to left of the posterior extremity. Thesecharacteristics were shared with Heligmostrongylus nematodes reported previously from O. phyllotis and Peromyscus yucatanicus (Cricetidae: Neotominae) also in the Yucatan Peninsula. The absence of intraspecific sequence variations in COI, and the low variation in D2-D3 expansion segments of 28S rRNA and ITS1 among the specimens obtained from the different hosts provided strong support that the worms found in the three rodent species belong to the same new species. The nine previously known species ofHeligmostrongylus have been reported from caviomorph rodents of the families Cuniculidae, Dasyproctidae, Echimyidae, and Erethizontidae from the Neotropics. The occurrence of H. yucatanensis in three phylogenetically distant rodent species suggests that this nematode species could have the ability to expand its host range by colonizing new hosts.