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placoid การใช้

ประโยคมือถือ
  • The skin of sharks is entirely covered by placoid scales.
  • Placoid scales are found in the cartilaginous fishes : sharks, enamel-like substance.
  • It is only known from placoid scales.
  • Bony fish have no placoid scales.
  • The placoid scales of cartilaginous fishes are also called dermal denticles and are structurally homologous with vertebrate teeth.
  • Placoid scales cannot grow in size, but rather more scales are added as the fish increases in size.
  • Their skin is smooth and largely covered by placoid scales, and their color can range from black to brownish gray.
  • Such skins are naturally covered with round, closely set, calcified papillae called placoid scales, whose size is chiefly dependent on the age and size of the animal.
  • Surprisingly durable, it is prepared in part by filing or grinding embedded placoid scales _ unique to sharks, skates and rays _ and by stretching and drying the skin.
  • He therefore adopted a classification which divided fish into four groups : Ganoids, Placoids, Cycloids and Ctenoids, based on the nature of the scales and other dermal appendages.
  • Members of this subclass are characterised by having five to seven pairs of gill clefts opening individually to the exterior, rigid dorsal fins and small placoid scales on the skin.
  • Members of the elasmobranchii subclass have no swim bladders, five to seven pairs of gill clefts opening individually to the exterior, rigid dorsal fins, and small placoid scales.
  • The jaws bear no teeth, but there are up to six or seven strong, short placoid scales above and below the mouth which meet when the jaws are closed.
  • Other distinctive characteristics include a strongly keeled caudal peduncle, highly textured skin covered in placoid scales and a mucus layer, a pointed snout distinctly hooked in younger specimens and a lunate caudal fin.
  • Many groups of bony fishes, including pipefishes and seahorses, several families of catfishes, sticklebacks, and poachers, have developed external bony plates, structurally resembling placoid scales, as protective armour.