Question

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Explain the main features of class cyclstoma ,chondrichthyes and osteicchthyes.



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Answer 1

Answer:

cyclostoma is jaw less fish,

chonsrichthyes: its endoskeleton is mead up by cartilage. tail is heterocircle.

Osteicchthyes: endoskeleton is mead up by bone and tail is homocircle

Answer 2

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☛The cyclostomes are

jawless fishes.

☛Endoskeleton is cartilaginous

☛They have suctorial tongue .

☛Notochord is persistent throughout life

☛Elongated body bearing 6-15 pairs of gill slits for respiration

Heart is 2-chambered

☛Ectoparasites

☛External fertilization

Ammocoetes larvae may be seen

Example : Petromyzon and Myxine

➽ Class Osteichthyes includes all bony fishes. Like all fishes, Osteichthyes are cold-blooded vertebrates that breathe through gills and use fins for swimming. Bony fishes share several distinguishing features: a skeleton of bone, scales, paired fins, one pair of gill openings, jaws, and paired nostrils.

➽ Apart from electric rays, which have a thick and flabby body, with soft, loose skin, chondrichthyans have tough skin covered with dermal teeth (again, Holocephali is an exception, as the teeth are lost in adults, only kept on the clasping organ seen on the caudal ventral surface of the male), also called placoid scales ...