Host range differences between two species of freshwater horsehair worm (Nematomorpha: Chordiidae) Chordodes japonensis and C. formosanus in Japan.

Horsehair worms (Nematomorpha: Gordioidea) are endoparasites of terrestrial arthropods, of which two species, Chordodes japonensis and C. formosanus, may have been historically confused due to their morphological similarity. In this study, we conducted field surveys and laboratory parasite inoculation experiments to clarify the characteristics and differences in host range and specificity between the two species. The field surveys revealed that the host ranges of the two species are markedly different. C. formosanus parasitized diverse mantids, while C. japonensis infected only species in the genus Tenodera, as predicted in previous studies. However, the two species had one mantid host, T. angustipennis in common. Parasite inoculation experiments using three species of mantids, revealed parasitism in each of the host-parasite combinations same as in the field study. These results suggest that the observed differences in host patterns are due to physiological factors between the host and parasite. Furthermore, cross-testing conducted on the shared host T. angustipennis showed that the two species coexisted within the same host in some cases, suggesting that the competitive exclusivity of the two species is low. This study also presents a tentative list of host ranges for the two species, comparing and integrating information from this and previous studies. However, the possibility remains that the host ranges of both species may be more diverse.

Molecular phylogeny of Japanese marine Tanytarsini chironomids (Chironomidae: Chironominae).

Tanytarsini is a large tribe of Chironomidae with at least 11 recorded marine species grouped in three genera. In this study, we performed a phylogenic analysis using molecular data from 13 Tanytarsini genera, including all Japanese marine species in a large tribe of Chironominae, to estimate their phylogenetic positions and evolutionary history. The phylogenetic reconstruction grouped the marine species in two clades. One clade was composed of five marine Tanytarsus and two marine Pontomyia species within a larger clade of Tanytarsus. Pontomyia is considered to have morphologically specialized and adapted to marine environments by rapid evolution, although it formed a clade with Tanytarsus. The only one species of Tanytarsus, T. pelagicus, clustered as a member of the second clade, which was mainly composed by species of the genus Paratanytarsus. Thus, we redescribe T. pelagicus as Paratanytarsus pelagicus.