Fine structural peculiarities of the pectoral fin dermoskeleton of two Brachiopterygii, Polypterus senegalus and Calamoichthys calabaricus (Pisces, Osteichthyes)

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Abstract
The features of the dermal skeleton of the pectoral fins of two Brachiopterygii, Polyterus senegalus and Calamoichthys calabaricus, have been studied by light and electrom microscopy. The components studied are the ganoine covered lepidotrichia segments and the distally located actinotrichia, the features of which are similar to those in teleosts. An irregular patch of ganoine susceptible to erosion by vascular canals lies on top of the cellular bone of the upper surface of the segment. It is separated from the stratified epidermis by an organic intermediate layer in place of the dermoepidermal interface. This layer is interpretated as “antislip pad” or elastic glue anchoring the epidermis on the hypermineralized ganoine. Such components are also observed in ganoid scales, although embryological data fail to support that lepidotrichial segments are modified scales. The lack of dentin in lepidotrichia emphasizes the tendency during evolution toward the reduction of some dermoskeletal components and exemplifies ganoine deposition directly on top of the bones as in holostei scale. The participation of neural crest cells in development of the dermal skeleton is discussed by way of the repartition of the odontods within the pectoral fin.