Morphological and molecular evidences for the existence of two new species of Homalometron (Digenea: Apocreadiidae), parasites of cichlids (Osteichthyes: Cichlidae)

Two new species of Homalometron Stafford, 1904 are described, one from the Sinaloan cichlid Cichlasoma beani (Jordan) in the upper Rio Santiago basin, Northwestern Mexico, and the other one from the Mayan cichlid Cichlasoma urophthalmus (Gunther) and the Redhead cichlid Vieja synspila (Hubbs) in Southeastern Mexico and Guatemala. Homalometron octopapillatum n. sp., from the intestine of the Sinaloan cichlid, differs from all congeners by having four pairs of oral papillae surrounding the mouth and by having vitellaria restricted to the hindbody. In addition, this new species is only found in that species of cichlid, which only occurs in river basins of Northwestern Mexico. The second species, Homalometron mesoamericanum n. sp., was considered to be conspecific with the type species, Homalometron pallidum Stafford, in several published accounts on the cichlid parasite fauna of Southeastern Mexico; however, detailed morphological examination of museum specimens as well as freshly collected specimens, along with a comparison through molecular data with H. pallidum from its natural distribution range in North America, allowed us to confirm that this represents, in fact, an undescribed species. The new species is distinguished from other congeners by the combination of the following characters: lack of papillae around the mouth opening, the anterior extension of the vitellaria (up to the anterior border of ovary), two compact eyespots next to pharynx and a large size (1,30-3,19). In this paper we followed an integrative taxonomy approach in which morphological characters are used in combination with data on two nuclear ribosomal markers (sequence divergence values and phylogenetic analysis), as well as data on host association and geographic distribution, to give further support to the recognition and description of two new species.