Discuss the important characters of the class chondrichthyes.

Explanation

Class chondrichthyes of vertebrata includes all the cartilaginous fishes. They posses the following general characters :
(i) The body consists of head, trunk and tail. Neck is absent.
(ii) The skin is covered by dermal placoid scales.
(iii) The endoskeleton is entirely cartilaginous.
(iv) The mouth is ventrai. The alimentary canal opens into the cloaca.
(v) The respiratory system includes 5-7 pairs of gills which are not covered by operculum. (vi) Swim bladder is absent.
(vii) The heart is 2-chambered, having one auricle the other ventricle.
(viii) There are 10 pairs of cranial nerves.
(ix) Excretory organ is kidney. Nitrogenous waste material is urea.