Question

Number of gills found in osteichthyes is
(a) Two pairs
(b) Four pairs
(c) Five pairs
(d) 6-15 pairs
(e) 12 pairs

Answer 1

Hint: Osteichthyes are the bony fishes that have bone as a major part of their endoskeleton. It is the largest class of vertebrates whose gill slits are protected by an operculum. The capillaries present in the gill slits helps in the transport of the oxygen to the tissues. 

Complete answer:
There are 4 pairs of gill slits found in the Osteichthyes. The gills help in the exchange of dissolved oxygen and carbon dioxide in water. The gills are present behind and to the side of the mouth cavity of fishes. It consists of fleshy filaments supported by the gill arches and filled with blood vessels. The water that enters continuously through the mouth passes backward between the gill bars and over the gill filaments, this is the place where the exchange of gases takes place.
- Any member of the superclass Osteichthyes is known as bony fishes, in the subphylum Vertebrata.
- More than 20,000 species and more than 400 families of modern bony fishes are from Superclass Osteichthyes. It also includes a few primitive forms.
- Bony fishes are found in all oceans and freshwater, including the underwater caves, deep- sea habitats, and thermal springs and vents. 
- The length of the members of this species may range from 0.5 inches to 15 feet for big fishes.
So, the correct answer is, ‘4 pairs.’

Note: The distinguishing characteristic of the bony fishes is its endoskeleton that should be partly composed of true bone (as opposed to cartilage). The swim bladder, gill covering over the gill chamber, bony plate- like scales, a skull with sutures, and external fertilization of eggs are the features of the members of the superclass Osteichthyes.