2. Habit and Habitat
➢ Bony fishes occur in all sorts of water: fresh, brackish, salt, warm and cold.
➢ Many species have protective spines on dorsal fins.
➢ Some fishes can change colours, and some can leave water and crawl on land.
➢ These are reared in aquarium in houses.
Temperature
➢ The body temperature is variable (poikilothermal)
3. Body Form
➢ Body is often spindle-shaped to facilitate movement through water.
➢ Body has 3 regions
○ Head
○ Trunk
○ Tail
➢ Neck is absent.
4. Appendages
➢ Fins are supported by cartilaginous or bony fin-rays.
➢ Pectoral and pelvic fins act as balancers and brakes during swimming.
➢ Pelvic fins lack claspers in both sexes.
➢ There is generally a single dorsal fin.
➢ Caudal fin is usually symmetrical.
➢ Tail helps to propel the fish by its
lateral movements & paired fins provide
fine control.
5. Skin
➢ Skin has epidermal unicellular
mucous glands and dermal cycloid,
ctenoid or ganoid scales.
➢ The scales are impermeable to
water.
➢ These reduce water loss in marine
environment and entry of water in
freshwater environment.
7. Digestive System ➢ Mouth is terminal.
➢ Alimentary canal opens out by anus (cloaca is absent).
➢ Intestine is long and lacks a scroll valve.
8. Respiratory System
➢ It consists of 4 pairs of filamentous gills.
➢ These offer larger surface area for gas exchange than the lamellar gills of cartilaginous
fishes.
➢ Gill slits are covered by operculum (gill covers).
➢ Some bony fishes have accessory air-breathing organs.
9. Swim Bladder
➢ Gas-filled swim bladder or air bladder is present.
➢ By altering gas pressure in it, the swim bladder acts as a buoyancy regulator.
➢ It enables the fish to stay at a particular depth.
➢ In some bony fishes, swim bladder is used as a lung for breathing air.
10. Circulatory System
➢ Heart is 2-chambered, having one auricle and one ventricle.
➢ Sinus venosus and conus arteriosus are present.
➢ Renal portal system is well developed.
➢ Red blood corpuscles are oval, biconvex and nucleated.
11. Cranial Nerves & Sense Organs
➢ There are 10 pairs of cranial nerves.
➢ Ear consists only of membranous labyrinth, having three semicircular ducts.
➢ Lateral-line sense organs are well developed.
➢ They detect vibrations and electric fields generated by other fishes or objects.
Excretory System
➢ Excretion is by a pair of kidneys.
➢ Nitrogenous waste matter is ammonia.
(ammonotelism
13. Fertilization & Development
➢ It is external.
➢ Most forms are oviparous.
➢ Life history may have a larval form.
➢ Some fishes show parental care of eggs.
16. Lung Fishes
➢ Protopterus (African Lungfish)
➢ Lepidosiren (South America lungfish)
➢ Neoceratodus (Australian Lungfish)
17. CLASS AMPHIBIA
General Characters
➢ Amphibians are tetrapod (Gr. tetra, four + pods, foot)
➢ Amphibia means dual mode of life.
➢ These can live in water as well as on land.
➢ Amphibians are the first vertebrates who made transition from aquatic to terrestrial mode of
life.
Habit and Habitat
➢ Amphibians occur in freshwater and moist land.
➢ There are no marine forms.
➢ Some frogs live on trees, e.g., Hyla (tree frog).
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19.
20. Temperature
➢ It is variable (poikilothermal) and most forms hibernate in winter.
➢ Some aestivate in dry summer.
Body Form
➢ It may be long and narrow or short and broad, depressed or cylindrical.
➢ It is divisible into head, neck , trunk and tail.
➢ In some forms neck is absent.
Appendages
➢ There are two pairs of pentadactyl limbs, each with 4-5 or fewer digits.
➢ Hindlimbs are larger than forelimbs in frogs and toads for leaping.
➢ These are nearly of same size in salamanders and newts.
21. ➢ In some amphibians limbs are absent (Apoda).
➢ Digits are without claws, nails or hoofs, and often have webs
Skin
➢ It is smooth, moist, rich in multicellular mucous and poison glands.
➢ It is highly vascular and is respiratory in most species.
➢ Scales are mostly absent (except Apoda).
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25.
26. Endoskeleton
➢ It is largely bony.
➢ Skull is flat and dicondylic, that is, has two occipital condyles.
➢ Notochord does not persist.
➢ First vertebra (atlas) is specialized to provide some movement to the head
27. Digestive System
➢ Mouth is large and armed with teeth in the upper or both the jaws.
➢ Teeth are acrodont.
➢ Amphibians (frogs and toads) are the first vertebrates to have a true tongue.
➢ A true tongue has muscles and is protrusible.
➢ Tongue is soft, mucus-coated and attached at the front end in frogs and toads.
➢ Alimentary canal leads into the cloaca.
28. Respiratory System
➢ Respiration takes place by
○ Lungs (Pulmonary respiration)
○ Lining of buccopharygeal cavity
○ Skin ( Cutaneous respiration)
○ Gills (Branchial respiration)
➢ Gills are always present in larvae, but may persist in the adult.
➢ Some forms have vocal cords and vocal sacs.
29. Circulatory System
➢ Heart is 3-chambered with two auricles and one ventricle.
➢ This is advancement over the 2-chambered fish heart.
➢ The left and right auricles receive blood from the lungs and the rest of the
body respectively.
➢ The ventricle pumps out mixed blood.
30. ➢ Sinus venosus and truncus arteriosus are present.
➢ Renal portal system is well developed.
➢ Red blood corpuscles are oval, biconvex and nucleated.
Cranial Nerves & Sense Organs
➢ There are 10 pairs of cranial nerves.
➢ There is no external ear.
➢ Middle ear with a single auditory ossicle is present in addition to the internal ear.
➢ Tympanum covers the middle ear.
➢ Lateral-line sense organs are present in larvae and in aquatic forms
31. Excretory System
➢ Excretion is done by pair of kidneys.
➢ Excretory waste material is ammonia in larval forms and urea in adults.
➢ Urinary bladder is present.
32. Reproductive System
➢ Gonoducts lead into the cloaca.
➢ Sexes are separate with sexual dimorphism
➢ Males lack copulatory organ.
Fertilization & Development
➢ Fertilization is mostly external (it is internal in salamanders).
➢ Most forms are oviparous.
➢ Some ovoviviparous.
➢ Life history often includes an aquatic larva (tadpole)
33. Parental Care
➢ Many amphibians show parental care.
➢ Male midwife toad (Alytes) carries eggs round the thighs.
➢ Female Surinam toad (Pipa) carries eggs in special pits on its back till tadpoles become
small frogs,
34. Origin
➢ Amphibians have evolved from lung-breathing, lobe-finned, bony fishes.
➢ Their paired fins had a fleshy lobe and gave rise to limbs.
➢ This ancestral group is at present represented by a ‘living fossil’ Latimeria.
Advancement ➢ Amphibians show advancement over the fishes in having
(i) pentadactyl limbs for movement on land,
(ii) eyelids and tear glands for protecting eyes on land,
(iii) middle ear to transmit aerial sound waves to the internal ear,
(iv) true tongue to capture food,
(v) internal nares and lungs for air breathing,
(vi) two auricles
