Morphological and molecular evidence for a new rhabdochonid species, Rhabdochona (Nematoda: Rhabdochonidae), parasitizing Eugerres mexicanus (Perciformes: Gerreidae), from the Lacantun River in the Biosphere Reserve of Montes Azules, Chiapas, Mexico

A new nematode species, Rhabdochona juliacarabiasae sp. n. is described from specimens recovered from the intestine of the freshwater Mexican mojarra, Eugerres mexicanus (Steindachner) (Gerreidae) captured in the Lacantun River, Chiapas, Mexico. Rhabdochona juliacarabiasae sp. n. is characterized by possessing a prostome armed with 12 anterior teeth (excepcionally 11), small bifurcated deirids with a markedly long base, an unusual tetrafurcate tip of the larger (left) spicule, a smaller (right) spicule without dorsal barb on its distal tip, and eggs with 1 short filament on each pole. In addition, in order to assess the phylogenetic relationships of the new species, and further demonstrate its distinctiveness against closely related congeners, specimens of R. juliacarabiasae sp. n, R. xiphophori, R. salgadoi, R. kidderi, R. canadensis, R. guerreroensis, and R. mexicana were sequenced for the cox1 gene, and the sequences were aligned with other nematode sequences available in GenBank (R. adentata, R. ahuhuellensis, R. ictaluri, and R. osorioi). Maximum likelihood and Bayesian inference analyses indicated that this new nested in a well-supported clade with high posterior probability. The molecular analyses support the validity of the new species. R. juliacarabiasae sp. n. was recovered as sister to the clade formed by R. kidderi and R. ictaluri, and shows genetic divergence that range between 11.18 and 14.89% (P- distances) compared with other congeners.

Automated summary

A new nematode species, Rhabdochona juliacarabiasae sp. n., was described from the intestine of a freshwater Mexican mojarra. Molecular analyses supported the validity of this new species, indicating its distinctive genetic divergence compared to closely related congeners. The new species was found to be sister to a clade formed by other related species, R. kidderi and R. ictaluri.