Placoid Scale

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Placoid Scale

a scale characteristic of cartilaginous fishes. It consists of a flat base (the basal plate), a neck, and a crown. Inside each scale there are several pulp canals or a cavity filled with pulp. A placoid scale is formed of dentin; its tip is covered with a harder, enamel-like vitrodentin. The scale originates between ectoderm and mesoderm, and, as it develops, it breaks through the ectoderm and emerges as a spine. Its formation is complete when the basal plate forms in the mesoderm. The placoid scale is constantly replaced during the life of a fish. In the evolution of vertebrates, the placoid scale precedes the more complexly structured ganoid scale. The teeth of vertebrates are derivatives of placoid scales.

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No references found			Placoid scales are like our teeth in that they are made of dentine. In the scales by Gilmore, R. Grant / Florida Sportsman Sharks have placoid scales, consisting of a rectangular base embedded in the skin with tiny spines that poke upwards from the surface, making them feel rough. Reducing the scale of drag by Engineer: The Professional Bulletin for Army Engineers The shark has skin made of teeth-sharp scales called placoid scales. What do you know about SHARKS? by GUYNUP, SHARON / Science World			placental barrier Placentation Placentia Placentia Bay Placer placer claim Placer County placer deposit placer dredge placer location placer mining Placerita Canyon State Park placeshifting Placetas placic horizon Placid Lake State Park Placid, Lake Placidia Placido Plácido placing placita Placode Placodermi Placodontia Placoid Scale Placothuriidae Placzek, Adolph K. Plafond Plagal Cadence plage Plaggept plagiaplite Plagiarism Plagiaulacida Plagiaulacidae plagiocephaly Plagioclase plagioclase feldspar plagioclimax plagiodont plagiogravitropism plagiohedral plagionite Plagiosauria plagiosere Plagiotropism PLAGO Plague Plague Revolt Plague Sunday			Placit placita Placitory Placitum Placitum Plack placket plackets Placobdella placode placode placoderm placoderm Placodermal Placodermata Placodermi Placodermi Placoderms Placoderms placodes Placodont Placodontia Placoganoid Placoganoidei placoid placoid Placoid fish Placoid fish Placoid fishes Placoid fishes Placoid Scale Placoides Placoides placoidian Placophora Placothuriidae Placque Placque Placque PLACS PLACT Placuna Placuna placenta Placzek, Adolph K. PLAD PLAD/CBTOS PLADO PLADS PLAE Plaek Khittasangkha PLAF PLAFIRE plafon fracture plafond plafond plafond plafond Plafond d'endettement Plafond Légal de Densité Plafond Mensuel de la Sécurité Sociale Plafond prix

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