Difference between bony and cartilaginous fishes?

Cartilaginous fish have a skeleton made of cartilage and bony fish have a skeleton made of bone.

Pisces (Fishes)

There are almost ##25,000## species of fish in this world. Pisces is a super class of the phylum Chordata. (Since half of chordates are fishes, they are grouped in the super class Pisces)

Fishes are divided into two classes:

##1.## Chondrichthyes: (Cartilaginous fishes)

This group is also called Elasmobranchi and is comprised of marine fishes. They possess the following characteristics:

1. They have an endoskeleton made up of cartilage.
2. Their skin consists an enormous number of tiny sharp enamel coated denticles called placoid scales which form the exoskeleton.
3. The wide mouth is ventral in position
4. The tail fin is heterocercal.
5. There are usually 5 exposed gill slits on each side not covered by a gill cover (i.e. the operculum).
6. Fertilization is internal

Examples are sharks, electric ray torpedo, skates, dog fishes, etc.

##2.## Osteichthyes: (Bony fishes)

This group is also called Teleostomi and its is the largest class of the phylum Chordata. They possess the following characteristics:

1. The endoskeleton in these fishes is made of bone.
2. Mouth opening is present at the anterior tip.
3. They are marine as wells fresh water fishes.
4. Exoskeleton which is made up of thin bony plates are called cycloid or ctenoid scales according to whether their outer edges is smooth or spiny.
5. The gills are covered over on each side by a gill cover called an operculum.
6. Most of these fishes have an air bladder that acts as a hydrostatic organ.
7. Tail fin is usually homocercal or diphycercal.
8. Fertilization is external.

This class includes eels, sea horses (which is actually a fish), globe fish, flying fish etc.