Arthropods are the first phylum to have well developed systems to carry out different activities. There is distinct system for respiration, locomotion and reproduction. Their survival capacity is great because of elaborate system. This has helped them survive in diverse conditions. They can live in water, on land and in air.
This can be one of the reasons why arthropods are the largest group among the animal kingdom. Another reason is their early development compared to animals of higher phylum.
