Morphological description and intraspecific variability of Mullus surmuletus (Teleostea, Mullidae) vertebral column

Morphological aspects of the vertebral column of Mullus surmuletus from the Sardinian Channel are highlighted. The total number of vertebrae proved to be constant (24) in all examined individuals and the most correct morphological subdivision appears to be into three regions (abdominal, caudal, and intermediate). A difference in the number of abdominal and intermediate vertebrae can be noted: respectively, 7+3 in 39% of individuals and 6+4 in the remaining 61%. The number of caudal vertebrae, however, is always constant (14). These differences were not influenced by size or sex. The present paper shows the first observations of variability, independently of depth or latitude, in the vertebral column of a species with subcarangiform swimming. Since variations in the vertebral composition are determined in the very early stages of ontogenesis, the observed differences might be caused by groups of individuals born in different periods of the same year, in which there could be differences in environmental parameters sufficient to determine variations in the vertebral morphology, but not in the number of vertebra