Pisces is a superclass which comprises all types of fishes. Pisces are further categorised into two classes. These classes are as follows:
1. Class Chondrichthyes: The body of these organisms is covered with placoid scales and they possess a cartilagenous skeleton. These organisms show internal fertilization and tail fins are assymtrical. External ears are absent in these organisms and operculum over the gills is absent. Examples of organisms belonging to class Chondrichthyes are Scoliodon, Pristis, Sphyrna and Chimaera.
2. Class Osteichthyes: The body of these organisms is covered with cycloid scales and they have a bony skeleton. The tail fins of these organisms are symmetrical and operculum is present over the gills. These organisms show external fertilization. Some of the examples of organisms belonging to class Osteichthyes are Labeo, Anabas, Hippocampus and Exocoetus.