General Characters of Chondrichthyes and Osteichthyes Dr. Pooja Agrahari Assistant professor Department of zoology c. M. science college, darbhanga Pisces • The superclass Pisces are the truly jawed vertebrates with specific organs for respiration, excretion and blood circulation related to permanently aquatic life. The organisms belonging to this class are poikilotherms, meaning that they cannot regulate their own body temperature. Essentially, all the fish come in this category. • Kingdom: Animalia • Phylum: Chordata • Class: Pisces Pisces Include three classes. 1. Placodemi 2. Chondrichthyes 3. Osteichthyes. Class : Chondrichthyes or Elasmobranchii 1. The class includes sharks, rays and chimaeras. These fishes are exclusively marine and predaceous. 2. Body fusiform or spindle shaped. 3. The exoskeleton in the form of placoid scales. 4. Their endoskeleton is cartilaginous and are called Cartilage without true bones. 5. Notochord persistent. Vertebrae complete and separate. 6. Pectoral and pelvic girdle present. 7. Mouth ventral. Jaw suspension is amphistylic or hyostylic. 8. Stomach J-shaped. Spiral valve is present in the intestine. 9. 5-7 pairs of gills are present. 10. External gill openings are separate. They are not covered by operculum. 11. Heterocercal caudal fin is seen. 12. Males show claspers for copulation. 13. Air-bladder and lungs are absent in these fishes. 14. Heart 2 chambered (1 auricle and 1 ventricle). The heart is with a sinus venosus, contractile conus arteriosus and bears rows of valves. 15. Temperature variable (poikilothermous). 16. Kidneys opisthonephric. Excretion ureotelic. Cloaca present. 17. Brain with large olfactory lobes and cerebellum. Cranial nerves 10 pairs. 18. Olfactory sacs do not open into pharynx. Membranous labyrinth with 3 semicircular canals. Lateral line system present. 19. Sexes are separate. Gonads typically paired and gonoducts open into the cloaca. 20. Eggs large and yolky. Fertilization internal. 21. Cleavage meroblastic. Development direct, without metamorphosis. Chondrichthyes • Examples – Shark, Chimaera, Skate fish, Ray fish Class: Osteichthyes or Telostomi The class Osteichthyes includes a large assemblage of true bony fishes. There are well over 30,000 to 40,000 living species, both freshwater and marine. Some of the freshwater forms are the carp, perch, bass, trout, catfish, sucker, etc., while the marine fishes are the tarpon, meckerel, tuna, sailfish, barracula, flying fish, etc. 1. These fishes are marine, fresh water and brackish water; warm or cold. 2. Body spindle shaped and streamlined. 3. Skin with many mucuous glands. Cycloid, ctenoid or ganoid scales will form the exoskeleton, no placoid scales. 4. Endoskeleton bony. Notochord replaced by distinct vertebrae. Pelvic girdle small and simple or absent. 5. Fins both median and paired, supported by fin rays of cartilage or bone. 6. Mouth terminal or subterminal. Jaws suspension is autostylic. 7. Cloaca lacking, anus present. 8. Claspers are absent. 9. Usually air bladder is present. 10. Tail homocercal. 11. Respiration by 4 pairs of gills on bony gill arches, covered by operculum. 12. Air bladder present with or without duct connected to pharynx. 13. Ventral heart 2-chambered (1 auricle and 1 ventricle). The heart is with a sinus venosus and conus arteriosus. Erythrocytes oval, nucleated. 14. Temperature variable (poikilothermous). 15. Adult kidneys mesonephric. Excretion ureotelic. 16. Brain with very small olfactory lobes, small cerebrum and well developed optic lobes and cerebellum. Cranial nerves 10 pairs. 17. Well developed lateral line system. Internal ear with 3 semicircular canals. 18. Sexes are separate. Gonads paired. 19. Eggs minute to 12 mm. Fertilization usually external. 20. Cleavage meroblastic. Development direct, rarely with metamorphosis. .