Structure and comparative morphology of camptotrichia of lungfish fins.

The present work is devoted to the organization and ultrastructure of the fin rays or camptotrichia of two living Dipnoi (lungfishes) Protopterus and Neoceratodus. In both species, these rods have a dual structure: only the superficial region facing the stratified epidermis is mineralized while the deep one is made of a dense unmineralized network of collagen fibrils forming a permanent pre-osseous tissue. Only the camptotrichia of Neoceratodus is made of cellular bone. This study confirms the structural peculiarities of these camptotrichia when compared to the dermal skeleton of the Actinopterygii constituted by the bony lepidotrichia and the actinotrichia. These results are discussed and compared to fossil dipnoan fin rays.