Latin , repere or reptum , to creep or crawl). They are mostly terrestrial animals and their body is covered by dry and cornified skin, epidermal scales or scutes (Fig. . ).
They do not have external ear openings. Tympanum represents ear. Limbs, when present, are two pairs. Heart is usually three-chambered, but four-chambered in crocodiles.
Reptiles are poikilotherms. Snakes and lizards shed their scales as skin cast. Sexes are separate. Fertilisation is internal.
They are oviparous and development is direct. Examples: Chelone (Turtle), Testudo (Tortoise), Chameleon (Tree lizard), Calotes (Garden lizard), Crocodilus (Crocodile), Alligator (Alligator). Hemidactylus (Wall lizard), Poisonous snakes – Naja (Cobra), Bangarus (Krait), Vipera (Viper). .
. . Class – Aves Class – Aves Class – Aves Class – Aves Class – Aves The characteristic features of Aves (birds) are the presence of feathers and most of them can fly except flightless birds (e.g., Ostrich). They possess beak (Figure .
). The forelimbs are modified into wings . The hind limbs generally have scales and are modified for walking, swimming or clasping the tree branches. Skin is dry without glands except the oil gland at the base of the tail.
Endoskeleton is fully ossified (bony) and the long bones are hollow with air cavities (pneumatic). The digestive tract of birds has additional chambers, the crop and gizzard. Heart is completely four- chambered. They are warm-blooded ( homoiothermous ) animals, i.e., they are able to maintain a constant body temperature.
Respiration is by Figure . Reptiles: (a) Chameleon (b) Crocodilus (c) Chelone (d) Naja (c) (d) lungs. Air sacs connected to lungs supplement respiration. Sexes are separate.
Fertilisation is internal. They are oviparous and development is direct. Examples : Corvus (Crow), Columba (Pigeon), Psittacula (Parrot), Struthio (Ostrich), Pavo (Peacock), Aptenodytes (Penguin), Neophron (Vulture). .
. . Class – Mammalia Class – Mammalia Class – Mammalia Class – Mammalia Class – Mammalia They are found in a variety of habitats – polar ice caps, deserts, mountains, forests, grasslands and dark caves. Some of them have adapted to fly or live in water.
The most unique mammalian