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There are various types of scales according to shape and Class . The scales of bony fishes are laid head to tail, reducing drag. COSMOID SCALES True cosmoid scales can only be found on the extinct Crossopterygians . The inner layer of the scale is made of lamellar bone. On top of this lies a layer of spongy or vascular bone and then a layer of Dentine like material called Cosmine . The upper surface is Keratin . The Coelacanth has modified cosmoid scales that lack Cosmine and are thinner than true cosmoid scales. GANOID SCALES Ganoid scales can be found on Gar s (family Lepisosteidae ) and Bichir s and reedfishes (family Polypteridae ). Ganoid scales are similar to cosmoid scales, but a layer of Ganoin lies over the cosmine layer and under the enamel. They are diamond-shaped, shiny, and hard. PLACOID SCALES Placoid scales are found on Cartilaginous fish and Shark s. These scales, also called Denticle s, are similar in structure to Teeth . LEPTOID SCALES Leptoid scales are found on the higher bony fishes and come in two forms, ctenoid and cycloid scales. Cycloid scales have a smooth outer edge, and are most common on more primitive fish with soft fin rays, such as Salmon and Carp . Ctenoid scales have a toothed outer edge, and are usually found on more derived fishes with spiny fin rays, such as Bass and Crappie . As they grow, cycloid and ctenoid scales add concentric layers. LEPIDOPTERAN WING SCALES image of a butterfly wing the scales are clearly visible, and the tiny platelets on each individual scale are just barely visible in the striping. ''© William Sharp, Arizona State University''. ]] Butterfly and Moth species of the order Lepidoptera ( Greek "scale-winged") have membranous wings covered in delicate, powdery scales. Each scale consists of a series of tiny stacked platelets of organic material. Because the thickness of the platelets is on the same order as the Wavelength of Visible Light the plates lead to structural coloration and Iridescence through the physical phenomenon described as Thin-film Optics . OTHERS Reptile scale types include: cycloid, granular (which appear bumpy), and keeled (which have a center ridge). |
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