Statolith-based species identification methods for ommastrephidae species

Statoliths are a pair of calcareous structures which can provide biological and ecological information for cephalopods. Understanding their shape will help us know the taxonomy of cephalopods, even to the species level. Ommastrephes bartramii, Dosidicus gigas and Illex argentinus are chosen to compare the shape of their statolith as a means of species identification because of their ecological importance to the marine ecosystems. The results show that D. gigas has a relatively large sized statolith and I. argentinus has the smallest. The four main parts of the statolith (dorsal dome, lateral dome, rostrum and wing) in the different species were diverse and distinguishable. The traditional method effectively separated the three species of statolith with high classification rates (92.0%–100%) by six morphology variables. The outline method produced a relatively low classification rate (73.4%–94.2%) using six harmonic numbers and stepwise discriminant analysis (SDA). The result in this study demonstrates that traditional method would achieve a better performance when the species are not so closely related phylogenetically, and outline method is more suitable for the statolith identification at the genus level. It is necessary to compare other cephalopod statoliths by different methods and find a suitable one.