Ontogeny of upper beak in Octopus vulgaris (Cuvier, 1797)

The beak is a fundamental component of the digestive system and is also used for age estimation in Octopus vulgaris. Nevertheless, the embryonic development of the beak is still largely unexplored. With this aim, upper jaws were observed and photographed using a wet coverslip with Differential Interference Contrast microscope. Pictures were analysed to obtain the measurements of upper jaws. We described the successive embryonic phases, and the beak structural features to assess the presence of pre-hatching increments in Lateral walls and the Rostrum. Three main phases were identified during the embryonic beak ontogeny. In a first phase the beak is a rudiment. The second phase begins when appears the layer originating the Hood. The third phase is characterized by the begin of sclerotization process. The Rostrum starts to be visible when embryos assume the hatching competence and the accuracy of the ageing method using the Rostrum surface was confirmed. On the contrary, several increments are visible on the lateral walls and none of them is related to specific embryonic event. A morphometric analysis was carried out, exploring similarities between growth pattern of different regions of the beak. In terms of growth rate, in the Rostrum the relative growth rate decreased in late ontogeny suggesting that modifications could be related with hardness, rather than size increase.In a second experiment the influence of temperature on beak growth was analysed. Using egg clusters reared at different temperatures, overall sizes of beaks and similarities between growth pattern of different beak regions are compared for a better understanding of the environmental effect in the beak development. In terms of beaks’ overall size, individual variability increased in the temperature conditions other than 19° and beaks reared at warm temperature, which were smaller than the rest of individuals. A relationbetween growth rate and areas of beak and effect of temperature was not confirmed