Variability and conservation in late chondrichthyan development: ontogeny of the winter skate (Leucoraja ocellata)

The ontogeny of the northwestern Atlantic batoid, Leucoraja ocellata, is described with special focus on the development of skate specific morphologies and the development of the fins. The results show that the sequence of events involving the early outgrowth of the paired fins and the initial development of the pharyngeal region is remarkably constant in skates, holocephalians, and sharks. However, differences exist in timing of the reshaping of the mandibular arch region, development of branchial filaments, median fins, denticles, and the order of branchial cleft formation. Despite the similarities of early events related to development of the branchial region and initial outgrowth of the fins, later stages are increasingly characterized by taxon-specific morphologies making a universal staging table for chondrichthyans less applicable. The staging table presented in this study represents an important resource for future studies on batoid embryology.