Gnathostomata is classified into two super classes:

1. Pisces
2. Tetrapoda

The `color{Violet }"classification"` is on the basis of :

`star` Locomotory organs
`star` Respiratory organs,
`star` Heart
`star` Blood vascular system.

● `color{Brown}"Respiration"`: Respiration is by `color{Violet}"gills"`, which are naked or covered by `color{Violet}"operculum"`. `color{Violet}"Air bladder"` helps in respiration in lung-fishes (Group - Dipnoi)



● `color{Brown}"Circulation"`: Heart is two chambered, known as `color{Violet}"Venous heart"` as it contains only impure blood, which goes to gills for purification from heart. The pure blood is then distributed to all parts of body directly from gills so there is `color{Violet}"single circulation of blood"`.



● `color{Brown}"Excretory Matter"`: Cartilaginous fishes excrete `color{Violet}"urea"`, Marine bony fishes excrete `color{Violet}"trimethylamine oxide (TMAO)"` and fresh water bony fish excrete `color{Violet}"ammonia"`. Urinary bladder is absent.

● Fishes are `color{Violet}"unisexual"`.

● Fertilization is internal or external.

● Development is `color{Violet}"direct"` i.e. larval stage is lacking during development.

● Baby fishes are called `color{Violet}"Fry or Hatchling"`.

Super class pisces classified into `color{Violet}"three"` classes:

`star` Placodermi

`star` Chondrichthyes

`star` Osteichthyes

● In this class, `color{Violet}"extinct fishes"` (Fossil fish) are included, which existed from `color{Violet}"devonian period to permian"` period.

● So these were the `color{Violet}"first fresh water"` `color{Violet}"true fishes"`.

● Their body was covered by `color{Violet}"bony plates"`, so these are called `color{Violet}"Armoured fishes"`

● Example: Climatius - `color{Violet}"First jawed fish"`