A new species of Wallinia Pearse, 1920 (Digenea: Allocreadiidae) in Astyanax mexicanus (Characidae) from Mexico revealed by morphology and sequences of the 28S ribosomal RNA gene.

Wallinia mexicana sp. n. is described from the Mexican tetra, Astyanax mexicanus (De Filippi) (Characidae Weitzman), from two localities in northern Mexico. The new species can be distinguished from the two congeneric species, described from small-bodied characids in South and Central America, mainly by the posterior extent of the vitelline follicles (halfway between the posterior testis and the end of the caeca), by having a larger oesophagus, testes that are always oblique, and eye-spot remnants. The distinct status of the new species was confirmed by molecular data (28S rRNA gene sequences). Phylogenetic analysis suggests the new species is the sister species of W. chavarriae Choudhury, Hartvigsen et Brooks, 2002 described from characids in northwestern Costa Rica. Additionally, genetic divergence between these congeners reached 3.3%, a value higher than that observed for closely related species pairs of allocreadiids for that molecular marker. Based on these new findings, recently published records of this new species as Magnivitellinum simplex Kloss, 1966 and Creptotrematina aguirrepequenoi Jiménez-Guzmán, 1973 in Astyanax mexicanus from Durango and San Luis Potosi states, respectively, are corrected.