Fluorescence Digital Image Gallery

Dogfish Shark Placoid Scales

The bodies of dogfishes, like all sharks, are externally lined with placoid scales, also known as dermal denticles. The scales, which unlike other types of fish scales do not get larger as the shark grows, are similar in structure to teeth, consisting of three layers: a hard outer enamel-like layer, a middle stratum of dentine, and a central vascular pulp cavity. The scales are arranged in a slanting pattern pointed towards the tail of the shark that helps decrease the amount of friction the animal incurs while swimming. If the surface of a shark is rubbed from head to tail, it feels smooth, but stroking the animal in the opposite direction causes it to feel very rough. Due to this fact, sharkskin has been used as sand paper for hundreds of years and was known as shagreen by European cabinetmakers.

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