Variability of the sulcus acusticus in the sagittal otolith of the genus Merluccius (Merlucciidae)

The morphology of the sulcus acusticus of the sacular otolith (sagitta) was studied by means of image analysis on 12 extant species of the genus Merlu ccius. The digitization of the sulcus acusticus and the subsequent biometri c analysis, by means of multivariate methods and the Fourier descriptors of the perimeters obtained, allowed the interspecific variability to be quant ified. These results were in agreement with ecomorphologic (functional and environmental) and phylogenetic aspects. Analysis of the perimeters of the sulcus acusticus demonstrated a specific character and indicated the existe nce of two large groups: the American species and the Euro-African species, matching the phylogenetic Lines. The principal difference between the two groups was found in the development of the caudal colliculum, which was rel atively shorter in the American species. Within the Euro-African group, the deep-water species M. polli and M. paradoxus showed different characterist ics with respect to the species from surface waters. Given the sensorial na ture of the associated acoustic macula of the inner ear the sulcus is more likely to accurately reflect the species specific changes in otolith morpho logy. (C) 2000 Elsevier Science B.V. All rights reserved.