Earthworm is the ordinary name for the larger members of the Oligochaeta (which is either a class or subclass depending on the author) in the phylum Annelida. In classical systems they were located in the order Opisthopora, on the basis of the male pores opening to the exterior of body posterior to the female pores, even though the male segments are anterior to the female. Cladistic studies have supported placing them instead in the suborder Lumbricina of the arrange Haplotaxida. Folk names for earthworm include "dew-worm", "night crawler" and "angleworm". Earthworms are also called megadriles (or big worms), as divergent to the microdriles, which include the families Tubificidae, Lumbriculidae, and Enchytraeidae, among others. The megadriles are characterized by having a multilayered clitellum (which is much clearer than the single-layered one of the microdriles), a vascular system with true capillaries, and male pores behind the female pores.
There are over 5,500 named classes known worldwide, existing everywhere but Polar and arid climates. They choice in size from two centimeters (less than one inch) to over three meters (almost ten feet) in the Giant Gippsland Earthworm. Amongst the main earthworm species usually found in temperate regions are the reddish colored, deep-burrowing Lumbricus terrestris.
In temperate zone areas, the most usually seen earthworms are lumbricids (Lumbricidae), mostly due to the recent rapid spread of a fairly small number of European species, but there are numerous other families, e.g. Megascolecidae, Octochaetidae, Sparganophilidae, Glossoscolecidae, etc.. These other families are often differing from the lumbricids in behavior, physiology and habitat.
