Super Class 1: Pisces

e The superclass Pisces of the truly jawed vertebrates Gnathostomata includes all the fishes which are essential aquatic forms with paired pectoral and pelvic fins for swimming and gills for respiration

Body usually spindle-shaped, streamlined and differentiated into head, trunk and tail. A neck is absent

Locomotion by paired pectoral and pelvic fins along with median dorsal and caudal fins, supported by true dermal fin rays

Muscular tail used in propulsion

Heart is 2-chambered (1 auricle, 1 ventricle) except lung fishes where heart is 3 chambered and venous or single circuit. Sinus venosus, conus arteriosus and renal portal. Erythrocytes nucleated. Poikilothermous. e Except lung fishes, they do not have internal nares

. Fishes have internal eare Skin usually moist and scaly They are divides into 3 classes : placodermi, chondrichthyes and osteichthyes

Class 1: Placodermi (Extinct) Fishes of this class had an external protective cover of bony scales or plates e.g., Climatius.

Class 2 : Chondrichthyes The cartilaginous fishes, most are marine. Body laterally compressed or dorsoventrally flattened. Pelvic fins bear claspers in male. They have heterocercal tail fin. Endoskeleton is cartilaginous and dermal placoid scales are present. Swim bladder is absent. Some of them have electric organs (e.g., Torpedo) They are cold-blooded (poikilothermous) animals, i.e., they lack the capacity to regulate their body temperature. They are oviparous or ovoviviparous. Development is direct

Class 3: Osteichthyes The body fishes. They occur in all sorts of water-fresh, brackish, salt, warm and cold. Body is often spindle shaped. Scales of 3 types present; ganoid, cycloid or ctenoid. Placoid scales are absent. Endoskeleton is

generally of bone (exception - Sturgeon). Four pairs of gills covered by an operculum. Mouth is mostly terminal, jaws usually with teeth. Heart 2 chambered. 10 pairs of cranial nerves are present. An air-filled swim bladder is present which acts as buoyancy regulator and enables the fish to stay at particular depth in water. They have internal ears, which help the fish to keep its balance. Lateral line system well developed. Fertilisation is generally external. Mostly

oviparous and development is mostly direct