A New Species of Ligophorus (Monogenea: Dactylogyridae) from the gills of the Flathead Mullet Mugil cephalus (Teleostei: Mugilidae) from Mexico.

A new monogenean species, Ligophorus yucatanensis n. sp. from the gills of the flathead mullet Mugil cephalus from the Yucatan Peninsula, Mexico, is described. The new species can be differentiated from all other species of Ligophorus by the morphology of the accessory piece of the copulatory organ. Its main lobe is cylindrical, tunnelled expanded distally, slightly bowed with a characteristic membranous opening at level of medial bifurcation of the accessory piece, forming a thick-walled bulbshaped expansion that ends in a round labium. The secondary lobe is spatulate, straight, and shorter than the main lobe. In addition, the new species can be distinguished from other species by the morphology of the haptoral ventral bar, and the distal end of the vaginal duct. Furthermore the ventral anchors are shorter than those of all other species of Ligophorus reported in the Gulf of Mexico and Caribbean Sea. In addition, the zoogeographical records of Ligophorus spp. on the M. cephalus species complex are briefly reviewed and updated.