Arthropods

Arthropods are the most varied and numerous group of animals on Earth. They have bodies divided into sections, jointed limbs, and a hard outer shell made of a material called chitin. This shell needs to be shed regularly so they can grow. Their bodies are arranged in segments, which are often joined together into larger functional parts. They can be found in almost every environment around the world, from the deepest oceans to the highest mountains, and from the coldest polar areas to the driest deserts. In the UK, they live on land, in freshwater, and in the sea. This group includes insects, spiders, crabs and lobsters, centipedes, and millipedes. All arthropods have bodies that are symmetrical on both sides and have a type of circulatory system where blood flows freely around their organs. Most have eyes made up of many small lenses, although the exact structure of their eyes can be quite different between different types. Their ability to adapt to many different environments has made them very successful. There are over a million known species of arthropods, which makes up about eighty percent of all known animal species.