First Report of Sex Chromosomes in Achiridae (Teleostei: Pleuronectiformes) with Inferences About the Origin of the Multiple XXXX/XXY System and Dispersal of Ribosomal Genes in Achirus achirus.

American soles (family Achiridae) have been characterized by remarkable chromosomal variation even though several species lack basic cytogenetic information. This trend indicates that chromosomal traits can be useful to taxonomy once the morphological identification of some taxa in this family (e.g.