Meeting Abstract
Most work on the morphology of notochords addresses issues related to the middle of this axial skeleton, where its geometry approximates that of a right, circular cylinder. In this middle region (precaudal and caudal) in Atlantic salmon, Salmo salar, the initially unsegmented notochord of the precaudal and caudal regions becomes segmented during development as chordacentra and then complete vertebrae form. But we know nothing about the morphological changes at the cranial and caudal termini. Using a variety of histological techniques, we examined the terminal morphologies of the notochord from embryo to adult. Surprisingly, the notochord at the cranial and caudal termini lacks regular segmentation, even at the adult stage. The adults’ urostyle, at the tail tip, persists as a notochord and shows irregular transverse septa, only some of which are complete. This stands in contrast to the cranial terminus of the notochord, which is mineralized, in part, before the precaudal vertebrae, develops very few of the vacuolated chordocytes that characterize the middle of the axial skeleton, and persists in adults as a remnant. In summary, the axial skeleton of salmon shows distinct developmental trajectories in at least three zones: cranial, precaudal-caudal, and urostyle. J.L. was supported by the National Science Foundation (USA, INSPIRE, Special Projects, grant no. 1344227).
