Question

Internal nares are absent in:
A) Agnatha
B) Chondrichthyes and Osteichthyes
C) Chondrichthyes
D) None of the above

Answer 1

Hint: They are the bony fishes. They have jawed vertebrates. Internal nares are absent in them but the external nares are present. These are soft, scaly fishes.

Complete Answer:
Internal nares have the choanae consisting of two apertures at the back of the nasal cavity which opens into the nasopharynx.
Nasopharynx is the open space that lies behind the nasal cavity in the airways.
Internal nares are also called posterior nasal aperture or posterior nares.

A) Agnatha belong to the class of Phylum and these are jawless vertebrates which have two nostrils but nares are absent in them.
B) Chondrichthyes belong to the class of cartilaginous fishes with a jawed vertebrate. External nares are present but the internal nares are absent.
C) Osteichthyes are the class of bony fishes and they are also having jawed vertebrates. Present nares are present but on the other hand, internal nares are absent.

Thus, the correct answer is option B. i.e., Chondrichthyes and Osteichthyes.

Additional information: Agnatha are the jawless fishes which are soft, scale less and mostly cylindrical in shape.
Examples are hagfish, lampreys. Chondrichthyes are the bony fishes having paired appendages with endoskeleton which is entirely cartilaginous. They have no swim bladder. Osteichthyes are the bony fishes that have no placoid scales. Mucus gland present in them that coats their body.

Note: Osteichthyes and Chondrichthyes belong to the class of bony and cartilaginous fishes. Internal nares are absent in them but on the other hand external nares are present.