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ganoid scale[¦ga‚nȯid ′skāl]
the scale of the lower radiant fishes, which is covered on the outside with a hard glittering layer of an enamel-like substance called ganoin. Two types of ganoid scale are distinguished: the palaeoniscoid ganoid scale found on fossil palaeoniscoids and modern multiscaled fishes, and the lepisosteid ganoid scale found on fossil vertebrate ganoids and modern long-nosed gars. The palaeoniscoid ganoid scale has a skeletal form of trough-shaped disks arranged to fit into one another, with an upper surface containing dentin ridges. The disks of ganoin grow symmetrically onto the foundation disks. In the lepisosteid ganoid scale there is no dentin, and the skeletal foundation is perforated by many canals. The shape of the ganoid scale is usually rhomboid. On the upper edge of each scale there is a projection that fits into a depression in the scale above it. By forming rings that are slightly slanted along the longitudinal axis of the body, the ganoid scale forms a shell, which in addition to its defensive function gives leverage to the muscles and necessary elasticity to the body.
V. N. YAKOVLEV