Early beak development in Argonauta Nodosa and Octopus Vulgaris (Cephalopoda: Incirrata) paralarvae suggests adaptation to different feeding mechanisms

Abstract

Morphological and morphometric development of the beak of Argonauta nodosa (oceanic species) and Octopus vulgaris (neritic species) paralarvae were analyzed in order to verify whether or not they are determined by distinct life strategies and habitats. Measurements were taken from the upper jaw (UJ) and lower jaw (LJ), compared by the t test to identify-specific differences, and correlated with mantle length (ML) by multiple linear regression to determine overall and relative influences on growth. The jaws of both species were fragile, lightly colored, presented dentition and a slit (division) in the LJ rostrum, and showed considerable variation in general aspect. The hood and lateral walls (UJ) and crest and wings (LJ) showed the highest correlation with paralarval size (ML), and were more developed in A. nodosa than in O. vulgaris of similar size. The rostrum of O. vulgaris seems to be less functional than that of A. nodosa. The presence of beak characteristics from ancestral cephalopod species in the jaws of early paralarvae, namely teeth and a slit in the LJ rostrum, and also the inability of small-sized A. nodosa paralarvae to close the jaws and bite off a piece of prey, seem to be related to the performance of external pre-digestion and suction of body fluids of prey, a specialized feeding mode.