Comparative morphological studies of the neurocranium and the gills of two species of blennies living in different habitats

Two species of Blennies – Salaria fluviatilis, which lives in freshwaters, and Salaria pavo, which lives in the sea – are considered to be phylogenetically related. Due to the interesting feature of one species having a freshwater and one having a marine habitat, and because of the paucity of studies on the intraspecific and interspecific variability of skeletal characters, in the study reported here, several populations of S. fluviatilis and S. pavo were compared. The intraspecific and interspecific morphology of the cranial characteristics, as well as the branchial epithelium, was studied in relationship to the adaptation of the two species to different environments. Osteological results confirmed the intraspecific variability already found in S. fluviatilis and showed a notable interspecific differentiation between S. pavo and S. fluviatilis. Histological studies indicate that the two species have morphological differences, which are the result of the diversity of the environments in which they live. The results from the two approaches, taken together, are in agreement with the hypothesis of the origin of these two species being from a common marine ancestor.