Comparative morphology of early stages of ommastrephid squids from the Mediterranean Sea

Trabajo final presentado por Giuliano Petroni para el Máster en Acuicultura de la Universitat de Barcelona (UB), la Universitat Autònoma de Barcelona (UAB) y la Universitat Politècnica de Catalunya (UPC) realizado bajo la dirección de la Dra. Mercè Dufort de la Universitat de Barcelona (UB) y del Dr. Roger Villanueva López del Institut de Ciències del Mar (ICM-CSIC).-- 20 pages, 10 figuresEarly life of oceanic squids is poorly known due to the difficulties in locating their pelagic egg masses in the wild or obtaining them under laboratory conditions. Recent in vitro fertilization techniques were used in this study to provide first comparative data of the early stages of the most important ommastrephid squid species from the Mediterranean Sea: Illex coindetii, Todaropsis eblanae and Todarodes sagittatus. Eggs, embryos and newly hatched paralarvae were described through development highlighting sizes and morphological differences between species. Duration of embryonic development in I. coindetii and T. eblanae was strictly correlated with temperature and egg size. Embryos of T. sagittatus were unable to reach hatchling stage and died during organogenesis. With the aim to distinguish rhynchoutheuthion larvae of I. coindetii and T. eblanae, particular attention was given to a few types of characters useful for species identification. The general structure of arm and proboscis suckers was described based on the presence of knobs on the chitinous ring. Chromatophore patterns on mantle and head were given for hatchlings of both species and showed some individual variation. A peculiar skin sculpture was observed under a binocular microscope on the external mantle surface of T. eblanae. SEM analysis revealed the presence of a network of hexagonal cells covered by dermal structures which may have a high taxonomic value. Few days old paralarvae had developed buccal masses and sensory organs on the epithelium, giving evidences for a presumed ability to feed actively. Comparisons between wild rhynchouteuthions collected from NW Mediterranean and freshly individuals artificially reared in the laboratory allowed identifying most specimens as I. coindetii on the basis of morphological features here described. The present study shows how in vitro fertilization techniques are highly effective in the study of the early life of oceanic squidsPeer Reviewe