Ultrastructural features of the dogfish Scyliorhinus canicula (Pisces: Scyliorhinidae) notochordal cells and the notochordal sheath

Abstract The dogfish Scyliorhinus canicula (Linnaeus, 1758) is a primitive cartilaginous fish, evolutionary placed among cephalochordates (Cephalochordata) and teleost fish (Osteichthyes). In this study we present the ultrastructural features of the dogfish notochordal cells and the notochordal sheath, revealed by light and electron microscopy. The dogfish notochord continuously passes through notochordal canal inside the vertebral centrum. It expands in the area of the intervertebral disc placed in between two adjacent vertebrae. Two notochordal cell types could be distinguished: marginal and central ones. Due to a significant intracellular and intercellular vacuolization central notochordal cells are thin and elongated, forming a net-like structure inside the notochord. The desmosomes are the usual type of junction between notochordal cells. The notochordal sheath of dogfish vertebra is an acellular structure composed of an elastic membrane surrounded by bundles of collagen fibres arranged in different orientations and directions. The ultrastructure of the dogfish notochord revealed a similar structure to those of other vertebrates including humans.