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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:
- They have an endoskeleton made up of cartilage.
- Their skin consists an enormous number of tiny sharp enamel coated denticles called placoid scales which form the exoskeleton.
- The wide mouth is ventral in position
- The tail fin is heterocercal.
- There are usually 5 exposed gill slits on each side not covered by a gill cover (i.e. the operculum).
- 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:
- The endoskeleton in these fishes is made of bone.
- Mouth opening is present at the anterior tip.
- They are marine as wells fresh water fishes.
- 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.
- The gills are covered over on each side by a gill cover called an operculum.
- Most of these fishes have an air bladder that acts as a hydrostatic organ.
- Tail fin is usually homocercal or diphycercal.
- Fertilization is external.
This class includes eels, sea horses (which is actually a fish), globe fish, flying fish etc.