1. Explain the general characters of Pisces.
Answer: Fishes are aquatic animals inhabiting fresh water, sea and brackish waters.
1. These are the first gnathostomes.
2. Devonian period is the golden age of fishes.
3. These are poikilothermous.
4. Body is stream lined and it is hydro dynamically designed.
5. Placoid, ganoid, ctenoid, cycloid and cosmoid scales are found in different fishes.
6. Fins are the locomotory organs. Pectoral and pelvic fins are paired fins.
7. Dorsal, ventral and caudal fins are the unpaired fins found in fishes. Caudal fin acts like a rudder.
8. Internal nares are found in lung fishes and Rhipidistians.
9. Polyphyodont, acrodont and homodont dentitions are seen.
10. Scroll valve or spiral valve that increases the absorptive surface of the intestine is found in some fishes.
11. Branchial respiration with the help of gills is seen in majority of the fishes. Counter current flow that facilitates the oxygenation is observed in gills.
12. Lungs are found in Dipnoi fishes.
13. In bony fishes, the fore gut projects out to form an air bladder. If this is used to improve buoyancy of the fish, it is referred to as swim bladder.
14. Two chambered heart is found. As the heart supplies blood only to gills, it is called branchial heart. As the deoxygenated blood alone is present in heart, it is also referred to as venous heart.
15. Mesonephric kidneys are present in fishes. In teleost, pronephros are found.
16. Fishes are normally ammonetelic but cartilaginous fishes are ureotelic.
17. The single membrane surrounding the brain is called meninx primitiva.
18. The neuromast organs found on the lateral sides of fish are called lateral line sense organs. These contain rheoreceptors that respond to water currents.
19. Majority of fishes are oviparous.
20. Cartilaginous fishes are viviparous with yolk sac placenta.
21. Rhinodon typus is the largest fish and Paedocypris progenetica is the smallest fish.
Short Answer Questions:
1. Mention the general characters of Chondrichthyes.
Answer: General characters of Chondrichthyes:
1. These are called cartilaginous fishes due to the presence of cartilaginous endoskeleton.
2. Heterocercal caudal fin is found.
3. Mouth is ventral in position.
4. Intestine contains a spiral valve that increases the absorptive surface.
5. Plate like lamelliform gills are found.
6. They retain urea in their blood. Hence they are not used for human consumption.
7. Claspers associated with pelvic fins are found in males.
8. Mostly viviparous and yolk sac placenta is seen.
2. Write short notes on Dipnoi.
Answer: These are commonly called Lung Fishes.
1. Body is covered by cycloid scales.
2. Dorsal and ventral fins are continuous with caudal fin.
3. Internal nostrils are present.
4. They exhibit discontinuous distribution.
5. Only three living genera are found at present.
6. As these are closely related to Osteolipids from which amphibians originated, these are called “uncles of amphibia” by Romer. e.g. Neoceratodus: This is Australian lung fish. It has only one lung.
Protopterus: It is African lung fish. It undergoes aestivation during summer.
Lepidosiren: It is a South American lung fish.
Very Short answer Questions:
1. What is branchial heart? Name the gnathostomes with branchial heart?
Answer. The heart that pumps the blood only to gills is called branchial heart. Fishes are the gnathostomes that contain branchial heart.
2. What are neuromast organs of fishes? What is their function?
A. The lateral line sense organs of fishes are called neuromast organs. They act as rheoreceptors.
3. Distinguish between pleurotrematic and hypotrematic elsmobranchs.
Pleurotrematic elasmobranchs: These are the elasmobranchs with five to seven pairs of lateral gill slits. They live in open waters. e.g.: Sharks.
Hypotrematic elasmobranchs: These are the elasmobranchs with five pairs of ventral gill slits. These are bottom dwellers. e.g.: Rays and Skates
4. Mention the generic name of electric ray. Name the structures that are modified in to electric organs in it.
A. Torpedo is the generic name of electric ray and in this dorsal muscles are modified to generate electricity.
5. What is a living fossil? Name a fish that is considered as living fossil.
A. Any animal that has undergone very little evolutionary change is called living fossil. Latemeria chalumnae is a living fossil in fishes.
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