Beak shape analysis and its potential to recognize three loliginid squid species found in the northeastern Pacific

Cephalopod beaks are chitinous structures used for species recognition. The family Loliginidae Lesueur, 1821 has historically been recognized for having taxonomic problems due to the lack of robust descriptors. Thus, in this study, we aimed at evaluating beak shape as a taxonomic character for Doryteuthis opalescens (Berry, 1911), Lolliguncula diomedeae (Hoyle, 1904), and Lolliguncula panamensis Berry, 1911 via geometric morphometrics. In addition, a thorough morphological description and an identification key were developed for upper and lower beaks of the three loliginid squid species. Our results indicated strong taxon differentiation based on beak shape, especially upper beaks, although both (upper and lower beaks) structures exhibited a strong discriminant power at the species level. The species-specific beak shape could be the result of differences in both feeding habits and habitat, possibly since the origin of the species due to the higher beak shape similarity between congeners. The beak shape description and taxonomic key are a reliable identification source for the three loliginid squid species. These materials are now available for users, especially those interested in determining the feeding ecology of predators when whole squid individuals are not available.