Animals belong to the largest and most diverse of the five kingdoms of living things. So far over two million animal species have been identified. All animals share certain features. Unlike plants, animals get the energy they need by eating food. They are all made up of many cells and many animals are highly mobile. Most reproduce sexually and have sense organs that allow them to react quickly to their surroundings. CLASSIFICATION uses these and other characteristics to group similar animals together.
In order to make animals easier to study, scientists divide the animal kingdom into divisions and subdivisions. The first division is called a phylum. Each phylum breaks down into groups called classes. Classes are divided into orders, then families, and then genera. Each genus contains species, which are individual groups of animals that have the same characteristics and can breed together.
Every animal species has a unique Latin name. The first word is the genus name, which is shared with closely related animals. The second word is the specific name, which, together with the genus, is unique to a particular species.
Animals are not classified by size. The giraffe and harvest mouse differ hugely in size but are both classified as mammals because they have fur, single-boned jaws, and suckle their young.
Animals are the only living things to have conquered the air. Insects, birds, and bats are all capable of powered flight. Birds have strong muscles to power their flight, coordinated by a well-developed brain and nervous system.
Animals can be very small. A mite is so small that it cannot be seen with the naked eye. Its size is limited because it can only grow by moulting (shedding its outer layer). Mites have a hard external skeleton and move on jointed legs. Other animals with these features include spiders and scorpions, many insects, and crabs.