question_answer 34)

  Give one example each for an animal possessing placoid scales and that with cycloid scales.

Answer:

                  Fishes possess dermal scales, each scale made of dentine that is secreted by dermal papilla. Placoid scales are hard and microscopic in size, their body is made up of dentine and exposed surface is covered with enamel, Cycloid scales are strong and extremely flexible. They are large, oval and made up of isopectine (layer of collagenous fibre). Placoid Scales are the characteristic features of cartilaginous fishes, (e.g., Scoliodon). Whereas, cycloid scale are found in bony fishes (e.g., Catia catia).