The myriapods comprise four classes of multi-legged arthropods with at least 18 legs (9 pairs) in adults. Two of these classes, the Diplopoda (millipedes) and Chilopoda (centipedes) primarily include relatively large-bodied, macroscopic organisms that are readily seen by the general public and are addressed in this website. The other two classes, Symphyla and Pauropoda, which lack common names, are microscopic organisms that are at most only a few mm in length and will not be addressed here. The Diplopoda and Chilopoda are ecologically important classes that occur throughout the temperate and tropical zones of the world and have been unintentionally introduced by man onto most oceanic islands. They are major components of terrestrial ecosystems including even xeric (desert) environments, yet they are poorly known and have been relatively ignored by past and present biologists.