Molecular and morphological characterization of Digenea (Rhodomelaceae, Rhodophyta) in the Mexican Atlantic

Abstract Digenea is a widely distributed genus in the Mexican Atlantic, and until a few years ago the only morphospecies D. simplex was recorded. Recent molecular research on this species from a locality in the Mexican Caribbean revealed the new species D. mexicana, whose morphological similarity with specimens from Gulf of Mexico suggests that its distribution range could extend to this area. The aim of this work was to characterize the molecular and morphological characters of Digenea specimens from different sites in the Mexican Atlantic, to confirm this hypothesis and even reveal the presence of new species or records for the country. Our phylogenetic analysis of COI-5P and rbcL markers revealed a new record of D. arenahauriens in Mexico and confirm the presence of D. mexicana in the southern Gulf of Mexico. The species delimitation methods showed potential new species for Australia, Japan, and Brazil. The true D. simplex was not recorded molecularly for Mexico. Morphological comparisons indicated an overlap among most of the species of the genus. Future studies about molecular and morphological characterization of Digenea specimens from around the world could help to clarify the problem of specific delimitation, and even reveal new species for the genus.