The use of the preorbital bone as a suitable method to identify Italian species of Mullets (Perciformes: Mugilidae)

In the Mediterranean sea the Mugilidae family is represented by 6 species: Chelon labrosus, Liza aurata, L. ramada, L. saliens, Mugil cephalus and Oedalechilus labeo. Taxonomic description of these species is based on several meristic characteristics. Nevertheless, the selection of these characteristics is controversial since there is a significant intraspecific variability, mainly among youngsters. The preorbital bone (a bone located in the anterior-lower limit of the orbit) has never been used as a taxonomic characteristic. The aim of this work is to compare preorbital bones of 6 Italian Mugilidae species and discuss the reliability of this bone as a taxonomic characteristic. Results obtained indicate that the morphology of the pre-orbital bone is a suitable diagnostic characteristic as it is immutable within species but presents important differences between species. In addition, bone morphology is stable within a species throughout all developmental stages, as opposed to meristic characteristics, used in taxonomical keys, which are not fully developed in the larval stage. Based on the morphometric study of the preorbital bone it has been possible to create a key descriptive-graphic which is an easy tool for swift taxonomical identification of individual Mullet species.