BIOLOGY PART 3

Animal Kingdom (Part-2)

K. Phylum: Chordata

पाइऱम: कोरडाटा

(Chorda dorsalis, the notochord is characteristic of this phylum)

1. All animals have a notochord either throughout life or during developmental stages only or it is replaced by a vertebral      column.

2. The central nervous system is dorsal, hollow and includes a single nerve cord. 3. Paired pharyngeal gill slits are                  present; they are functional throughout life or only during embryonic developmental stages.

4. They possess a post-anal tail.

5. They have a closed circulatory system with a ventral heart and haemoglobin in erythrocytes.

6. Animals are eucoelomates.

7. They show organ-system level of organisation and are triploblastic.

(i) Sub-Phylum: Cephalochordata

उऩ-पाइऱम: सेपऱोकाडेटा

e.g., Branchiostoma (Amphioxus).

(ii) Sub-Phylum: Urochordata

उऩ-पाइऱम: उरोकाडेटा

e.g., Salpa, Doliolum, Ascidia, etc.

(iii) Sub-Phylum: Vertebrata

उऩ-पऱम: कशेरुकाता

1. Notochord is present in the embryonic stages and is replaced by the vertebral column in adults.

2. They have a closed circulatory system with a ventral heart with two, three or four chambers and haemoglobin in the red blood cells (erythrocytes).

3. Animals have kidneys for excretion and osmoregulation.

4. Paired lateral appendages are present in the form of fins or limbs.

(a) Class: Cyclostomata

वर्ग: साइक्ऱोस्टोमेटा

(Cyclo-circular; stoma-opening/mouth; hence the animals with circular mouth opening called cyclostomates)

1. Characteristically, they have a circular. Suctorial mouth, without jaws.

2. They are ectoparasites on other fishes.

3.6-15 pairs of gill-slits are present

4. Body lacks scales and paired fins

5. Cranium and vertebral column are cartilaginous.

6. Circulation is of closed type.

7. Animals are marine, but move to freshwater spawning; within a few days after spawning, they die.

(b) Class: Chondrichthyes

वर्ग: कान्ड्रिकथिस

(Animals are commonly called cartilaginous fishes (chondro-cartilage; ichthyes-fish), as their endoskeleton is cartilaginous)

1. Body is fusiform/streamlined with cartilaginous endoskeleton.

2. Body is covered by placoid scales.

3. Mouth is ventral; teeth are modified placoid scales and are pointed backwards.

4. Jaws are powerful and animals are predaceous.

5. 5-7 pairs of gill-slits are present, they are not covered by operculum.

6. Air-bladder is absent and animals have to swim constantly to avoid sinking.

7. Heart is two-chambered.

8. Animals are poikilotherms fcold-blooded).

9. Some animals like Torpedo possess electric organs and some like Trygon possess poison sting.

10 Animals are unisexual; fertilisation is internal and many are viviparous. e.g., Scoliodon, Trygon, Pristis, Carcharodon, etc.

(c) Class: Osteichthyes

वर्ग: ओन्ड्स्टकथिस

(Animals are called bony fishes (osteo-bone; ichthyes-fish) as they have a bony endoskeleton)

1. Body is streamlined with bony endo skeleton.

2. Body is covered by cycloid/ctenoid scales.

3. Mouth is terminal.

4. They have four pairs of gill-slits, covered by an operculum.

5. Air-bladder is present.

6. Heart is two-chambered.

7. Animals are poikilotherms.

8. Sexes are separate; fertilesation is external and development is direct. e.g., Erocoetus, Hippocampus, Labeo, Catla,            Pterophyllum, Betta, etc. 

(d) Class: Amphibia

वर्ग: उभयचर

(Animals show dual mode of life (amphi - two/ dual; bios – life), i.e., both terrestrial and in water during breeding season)

1. Body is divided into head and trunk and tail is present in some; neck is absent.

2. The trunk bears two pairs of limbs

3. Skin is moist and has mucous glands.

4. Eyes are large and projecting to compensate for the absence of neck.

5. Tympanum (ear drum) represents the ear.

6. Heart is three-chambered, with two auricles and one ventricle.

7. Alimentary canal, reproductive system and urinary system open into a cloacal chamber that opens to the outside                through cloacal aperture.

8. Animals are poikilotherms.

9. Respiration is by lungs (on land), by skin while in water and by gills in tadpoles.

10. Sexes are separate; animals are oviparous with external fertilization.

11. Development involves a tadpole larva. e.g., Ichthyophis. (Limbless amphibian), Bufo, Rana, Salamandra, etc.

(e) Class: Reptilia

वर्ग: रेन्ड्टटलऱया

(Because of their creeping or crawling habit, animals are called reptiles).

1. Body is divided into head, neck, trunk and tail.

2. Skin is dry without glands and body is covered by horny/cornified skin or epidermal scales, called scutes. - Snakes and      lizards shed their scales a skin-cast.

3. Tympanum represents the ear.

4. Trunk bears two pairs of limbs.

5. Heart is three-chambered, except crocodiles, where it is four chambered. 

6. Animals are unisexual; fertilisation is internal and they are ovoviviparous, i.e., the egg contains a fully-developed              young one at the time when it is laid, development is direct. e.g., Calotes, Chameleon, Hemidactylus, etc. Poisonous          snakes: Vipera – Viper, Naja – Cobra, Bangarus – Krait, etc.

f) Class: Aves

वर्ग:ऩक्षी

(Aves-birds; animals show aerial mode of life).

1. Body is divided into head, neck, trunk and tail.

2. Body is covered by feathers and they can fly except a few like ostrich.

3. Jaws are modified into beaks; teeth are absent.

4. Skin is dry without glands, except the oil/preen gland at the base of tail.

5. Forelimbs are modified into wings and covered by feathers; hindlimbs have scales and are modified for walking,                perching, swimming, running, etc.

6. Endoskeleton is bony and bones are hollow with air cavities; such 'bones are called pneumatic bones.

7. Digestive tract has two additional chambers crop and gizzard.

8. Heart is four-chambered and there is double circulation.

9. Animals are homoiotherms.

10. Respiration is by lungs and the air sacs connected to lungs supplement respiration.

11. Animals are unisexual and exhibit sexual dimorphism; fertilisation is internal and animals are oviparous and                      development is direct. e.g., Corvus, Pavo, Neophron, Struthio, etc.

(g) Class: Mammalia

वर्ग: स्तनधारी

(Mammae-mammary glands; hence animals are called mammals)

1. The characteristic feature of the class is the presence of mammae or mammary glands, which are vestigeal in males,            but functional in females; the milk produced by them is used to nourish the young ones.

2. Presence of hair on the body is also a unique feature.

3. External ear or pinnae are present.

4. Diaphragm is the muscular partition that divides the trunk internally into thoracic and abdominal cavities.

5. Heart is four-chambered and there is double circulation.

6. Animals are homoiotherms.

7. Respiration is by lungs in all, irrespective of the habitat.

8. Fertilisation is internal and animals are viviparous with a few exceptions like Ornithorhynchus, which is                             oviparous, but has mammary glands. e.g., Macropus, Homo sapiens, Canis, Felis, Camelus, etc.