Beak development of early squid paralarvae (Cephalopoda: Teuthoidea) may reflect an adaptation to a specialized feeding mode

Morphological and morphometric development of the upper jaw (UJ) and lower jaw (LJ) and arm crown of Chiroteuthis cf. veranyi, Liocranchia reinhardti (oceanic species), and Doryteuthis opalescens (neritic species) paralarvae were analyzed in order to verify whether or not they are determined by developmental modes. Jaw measurements were taken, correlated with mantle length (ML) by multiple linear regression to determine relative influences on growth, and compared between species by ANOVA to identify differences. Development was expected to be similar between oceanic species, but was morphologically similar between L. reinhardti and D. opalescens, and morphometrically similar between the latter and C. cf. veranyi. UJ and LJ measurements with highest correlation with ML are larger in L. reinhardti, indicating greater beak development in this species. Rostrum robustness is higher in L. reinhardti, intermediate in D. opalescens, and lower in C. cf. veranyi, hinting at the respective prey type. Teeth (LJ) and slit, characteristics of ancestral cephalopods, are present, disappearing completely and partially on the largest specimens of L. reinhardti and D. opalescens, respectively, and remaining in all sizes of C. cf. veranyi. The results suggest that their presence in early paralarvae reflects an adaptation to sucking the pre-digested internal fluids of prey.