Class Osteichthyes - NEET-Biology

Class Osteichthyes

Fig: Catla fish 

• The vast majority of vertebrates belong to a superclass of gnathostomes called Osteichthyes.

• Unlike chondrichthyans, nearly all living osteichthyans have an ossified (bony) endoskeleton with a hard matrix of calcium phosphate [Ca3(PO4)2].

Important characteristics:

• It includes both marine & freshwater fishes with a bony endoskeleton.

• They have four pairs of gills that are covered by an operculum on each side.

• The heart is two-chambered (one auricle & one ventricle).

• Most fishes can control their buoyancy with an air bladder known as the swim bladder. 

• Movement of gases from the blood to the swim/air bladder (fish maw) increases buoyancy, making the animal rise; transfer of gas back to the blood causes the animal to sink.

• Adult kidneys are mesonephric. Excretion is chiefly ammonetelic.

• They are cold-blooded animals.

• Sexes are separate. Fertilization is usually external.

• Mostly oviparous, rarely ovoviviparous or viviparous.

• Development direct, rarely with metamorphosis.

• Examples: Latimeria (Lobe-finned fish), Dipnoi (Lung-fish), Hippocampus (Sea-horse), Exocoetus (Flying fish), Echeneis or Remoro (Suckerfish), Anguilla (eel), Anabas (Climbing perch), Catla-Catla (Catla), Pterophyllum (Angelfish), Betta (Fighting fish).

Fig: Dipnoi (Lung-fish)