The animal world

The animal world (fauna) differs from plants: it can move freely, feeds mostly heterotrophically, and most animals have a developed nervous system. An animal body consists of organ systems (digestive, respiratory, circulatory, excretory and others); systems are made of organs (heart, lung, liver, kidney), organs of tissues, and tissues of cells. Animals have four kinds of tissue: protective (covering), connective, nervous and muscle. In nature animals take part in food chains; some are nature’s sanitary workers (earthworm, dung beetle), bivalve molluscs clean water, birds and rodents spread seeds, and bees and butterflies pollinate plants. People get meat, eggs, wool and milk from animals, use horses and donkeys for transport and dogs as guards; flies and mosquitoes spread disease. In animal classification the units are: species → genus (called “urug‘” in the book) → family → order (“turkum”) → class → phylum (“tip”) → animal world. Animals with a backbone are vertebrates (phylum Chordata: fish, amphibians, reptiles, birds, mammals); invertebrates include the phyla of protozoa, coelenterates, flatworms, roundworms, annelids, molluscs and arthropods. For example the domestic cat: phylum – chordates, class – mammals, order – carnivores, family – cats (felids), genus – cat, species – domestic cat.