Division (2) Gnathostomata (1) These are developed vertebrates. (2) Mouth is encircled by true jaws. (3) Movement by paired fins or legs. (4) Vertebral column well developed. (5) Mouth is not rounded. (6) Pineal eye is absent. (7) 3 Semi circular canals are found in internal ear. (8) Animals are unisexual, gonads are paired, genital ducts are present. (9) Gills or lungs are meant for respiration. Group Gnathostomata is classified into two super classes on the basis of locomotory organs, respiratory organs, heart, nostrils and blood vascular system. [2] Super Class of G-nathostomata : [1] Pisces [2] Tetrapoda [1] SUPER CLASS - PISCES (1) This superclass includes true fishes. (2) Animals are aquatic, may be fresh water or marine. (3) These are cold blooded or poikilothermic animals. (4) Body is long, boat shaped and stream lined, which is divided into head, trunk and tail. Neck is absent. (5) Body is covered by dermal scales. Exceptions :- 1. Cat fish 2. Torpedo Both these fishes are scale less. (6) Paired fins are present for swimming, e.g. Pectoral and pelvic fins, along with these fins are also found on the body e.g. mid dorsal fin and caudal fin. (7) Endoskeleton is made up of cartilage or bones. (8) External nares are one pair. This condition is known as Dirhynous condition. (9) Respiration by gills, gills are 5 to 7 pairs and naked or covered by operculum. (10) Heart two chambered, known as “Venous heart”, because it contains only impure blood, which goes to gills for purification from heart. Pure blood is then distributed to all parts of body directly from gills, i.e. circulation of blood is unicircuit. (11) Their RBC (Present in blood) are nucleated. Sinus venosus, renal and hepatic portal systems are found in circulatory system. (12) External and middle ears are absent, only internal ear is present in which three semi - circular canals are present, which work as statoreceptor. (13) Kidneys in fishes are mesonephric type. Cartilagenous fishes excrete urea and marine bony fishes excrete trimethylamine oxide. (14) Cranial nerves are 10 - pairs. (15) Lateral line receptor system is present in the body of fishes, which includes many organs. (16) “Air bladder” helps in respiration in lung-fishes (Group - Dipnoi) (17) Vertebrae in fishes are amphicoelus, in which centrum is concave at both the surfaces. (18) Fishes are unisexual. (19) Fertilization is internal or external. Females are oviparous or ovoviviparous. (20) In the skull of fishes only one occipital condyle is present, so their skull is called monocondylar type. (21) Eggs are mesolecithal or megalecithal type. (22) Cleavage in fishes is holoblastic unequal, or meroblastic discoidal type. (23) Extraembryonic membranes are absent in fishes so all the fishes are placed under anamniota. (24) Metamorphosis is direct i.e. larval stage is lacking during development. (25) Small fishes (Baby fishes) are called “FRY”. (26) Fishes show a seasonal migration in a particular season. [A] Migration of fishes from fresh water to marine water is called catadromous migration. Example :- Anguilla [B] Migration of fishes from marine water to fresh water is called Anadromous migration. Example :- (1) Salmon (2) Sturgeon (3) Hilsa (4) Trout (27) “Devonian era” is called “era of fishes” Study of fishes is Icthyology. Romer classified super class pisces into three classes :- Super Class Pisces classify into three classes :- (A) Class - Placodermi (B) Class - Chondrichthyes (C) Class - Osteichthyes (A) CLASS - PLACODERMI :- (1) In this class, all extinct fishes are included, which lived from devonian period to permian pe- riod. So these were the “first fresh water true fishes”. (2) Their entire body was covered by bony plates, so these were called “Armoured fishes” Examples 1. Dinicthyes 2. Coccosteus 3. Climatius - first jawed fish (B) CLASS CHONDRICHTHYES OR ELASMOBRANCHI :- (1) This class includes cartilagenous fishes. (2) Fishes are normally marine of this class. (3) Endoskeleton is made up of cartilage. (4) Exoskeleton over the skin is made up of placoid scales. These scales are like denticle and are originated by dermis of skin. (5) In these fishes, 5-7 pairs of gills are present, which open directly outside the body by gill slits, operculum is normally absent in these fishes. (6) 5 pairs spiracles are found in them. Exception :- Fishes of group Holocephali have operculum over their gills. Example :- Chimaera (Rat fish) 5. Stegostoma :- Tiger shark 6. Trygon :- Sting ray - Its dorsal fin has poisonous spines. 7. Torpedo :- Electric ray - In this fish an electric organ is found which is a modified muscle it can give shock of about 100 volts. It is exoskeletonless. 8. Rhineodon :- Whale shark - It is the largest true fish. Its length is 13 - 14 mt 9. Carcharodon :- Greate white shark. 10. Chimaera :- “Rat fish” or “King of herrings” or ghost fish. Chimaera is supposed to be the connecting link between bony and cartilagenous fishes. 11. Raja :- Scate 12. Myliobatis :- Eagle - Ray Note :- Dry skin of cartilagenous fishes is called “Sagreen” [C] CLASS - OSTEICHTHYES OR TELEOSTOMI :- (1) Fishes of this class are found in fresh water as well as marine water. (2) Body is spindle shaped and boat - shaped. (3) Their exoskeleton is made up of scales, which may be cycloid or ctenoid or ganoid Placoid scales are absent. (4) Mouth is normally terminal or subterminal, teeth are found in Jaws. (5) Endoskeleton of these fishes is made up of bones, so these fishes are called “bony - fishes” (6) Notochord is modified into vertebral column. Pelvic girdle is simple, small or may be absent. (7) Respiration by 4 - pairs of gills. These gills are covered by operculum at each side of body. (8) Spiracles are absent. (9) Helping respiratory organs “air-bladders” are present. Lung fishes respire through air bladders. In other fishes these air bladders are hydrostatic i.e. help in maintaining balance of body. (10) Scroll valve in intestine and ampulla of Lorenzini are absent. (11) Internal nares are present. (12) Liver is trilobed. (13) Cloaca absent, in place of cloacal aperture anus is present. (14) Tail is normally homocercal type but sometimes it may be diphycercal type. (15) Heart two chambered, sinus venosus and bulbous arteriosus are present. (16) Genital ducts open outside the body through separate apertures. (17) These fishes are unisexual. (18) Fertilization is external and claspers are absent in male fishes. (19) Female fishes are oviparous but may be ovoviviparous Examples (1) Labeo :- “Rohu”or “Indian carp” - It is a fresh water fish. (2) Clarius :- “Cat fish” or magur (3) Hippocampus :- “Sea - horse” or “Pregnant male” :- It swims in water in its vertical position. A pouch like structure is present at the abdomen of male fishes known as “Brood - pouch”. In this pouch male collects the eggs. Secondary vivipary and parental care is found in hippocampus. (4) Anabas :- Climbing perch. (5) Exocetus :- Flying fish - Its dorsal fin is long, it can fly (glide) over 400 metre with the help of this fin. (6) Amia :- Bow - fish. (7) Anguila :- Eel :- Its body is snake like (8) Acipensor :- Sturgeon - endoskeleton is made up of cartilages. (9) Echeneis :- Sucker fish - Dorsal fin modified into suckers. Shows commensal with shark. (10) Pleuronectus :- Flat fish (11) Latimaria :- Living fossil fish :- It is the oldest living vertebrate known till now. (12) Opsanus :- Toad fish (13) Syngnathus :- Pipe fish (14) Synanceja horrida :- Stone fish .- It is the most poisonous fish. (15) Lepidosteus :- Gar - pike (16) Harpodon :- Bombay duck. (17) Gambusia :- Larvivorous fish. (18) Fistularia :- Flute fish. Dipnoi :- These are called “lung fishes”, because their air bladder help in respiration. (1) External and internal both the nares are present. (2) Their tail is heterocercal type. These are freshwater fishes. Fishes of dipnoi group are called Lung - fishes or “Uncle of amphibians” Example 1. Protopterus : African lung fish :- It is living fossil fish. 2. Lepidosiren :- South american lung fish. 3. Neoceratodus :- Australian lung fish. SPECIAL (IMPORTANT) POINTS (1) Cycloid, ctenoid, ganoid scales are mesodermal in origin. (2) Scroll valve present in the intestine of some fishes increases the absorptive surface area. (3) Scoliodon and Mustellus fishes are viviparous. Fish liver oil is rich in Vit - A & D Shark liver oil is rich in Vit - A Cod liver oil is rich in Vit - D (4) Lung fish remains alive outside the water, but rest of the fishes require water for gill respiration. (5) Fishes can change their direction of swimming at any time by their caudal fin. (6) Egg capsule of Sharks and Skates refers to “Mermaid purse” (7) Issinglass is gelly like substance obtained from air bladder of certain fishes it is used for clari- fication of wines and Beers. (2) Superclass - Tetrapoda (1) Members of this superclass are found in water and on land. (2) Locomotion by 2 pairs of pentadactylous limbs. (3) Gills are present only in embryonic stages. Main respiratory organ in adults is lung. (4) Exoskeleton is made up of scales, feathers or hair. (5) Endoskeleton is made up of bones. (6) Heart is three or four chambered and double circulation is found in them. (7) Kidneys are mesonephric or metanephric type. (8) Middle ear is present. Birds and mammals have external ears also. Superclass - Tetrapoda is divided into four classes Class [A] - Amphibia Class [B] - Reptilia Class [C] - Aves Class [D] - Mammalia Class amphibia includes amphibious animals which can live on both the places i.e. - under water and on the land. These are the first chordate animals which come out from the water but these are not able to live on land permanently, they depend on water for their reproduction. Class amphibia shows the double nature of animals. Amphibia class is placed between pisces class and reptilia class and they are originated in Devonion period.