The word ‘Animal’ is derived from the word ‘Animalis’ in Latin which means ‘having breath.’ As they grow the body plan finally becomes fixed but some of them go through a process called metamorphosis which means change. Animals are divided into different groups like mollusks (oysters, snails) vertebrates (mammals, birds, fish, amphibians) annelids (leeches, earthworms, centipedes, millipedes) arthropods ( spiders, lobsters, crabs, shrimps) jellyfish and sponges.
Animals have many characteristics such as they are multicellular, they digest food in an internal chamber, they are motile and the embryos pass through a stage called ‘bastula’ which is unique in animals only.
All animals reproduce by sexual reproduction or by asexual reproduction. In sexual reproduction they have reproductive cells which produce spermatozoa or ova and form zygotes which develop into a new animal. In asexual reproduction the fertile eggs are produced by fragmentation or budding and not by mating.
According to their food habits animals can be divided into herbivores, carnivores and omnivores. Herbivores are those animals that eat only plants- cow, goat and rabbit. Carnivores are those animals that eat only flesh- cat, dog, and tiger. Omnivores are those that eat both plants and animals-bear.
`Animals can be classified into vertebrates and invertebrates. Those with backbones are called vertebrates and those without are called invertebrates. Five well-known vertebrates’ are-mammals: When an animal drinks its mother’s milk it is known as mammals. Dog, cat, horse, kangaroo. Birds are animals that have feathers-peacock, sparrow, crow, pigeon. Fish live in water and have scales, fins, and gills in their body. Reptiles have scaly skin and are cold blooded- snakes, lizards. Amphibians are those that live both on land and water-frogs.