|Megascolecidae castings in India|
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The Megascolecidae are a large family of earthworms which has native representatives in Australia, New Zealand, Southeast and East Asia, and North America. The most ancient lineages of the family show a Gondwanan distribution and have been used as evidence of continental drift. Members of the Pheretima group of genera (e.g. Amynthas) are widely distributed around the tropics, much as some Lumbricidae are distributed through the temperate zones. Some North American native genera – e.g. Arctiostrotus, Argilophilus and Driloleirus – also belong to this family.
The members of this family have the typical "megascolecine" arrangement of male pores, with vasa deferentia and prostatic ducts uniting before opening via a combined pore on segment 18, rather than the "acanthodriline" arrangement (with male pores and pores from one or more pairs of prostates opening separately near segment 18, but never combined on segment 18) as found in the related families Acanthodrilidae, Octochaetidae and Exxidae.
Megascolecidae genera are either meroic (with multiple nephridia per segment), or have the plesiomorphic holoic arrangement of two nephridia per segment. Some taxa also exhibit enteronephry, where some nephridia, instead of emptying to the body surface, empty into the digestive tract. Setae may be lumbricine (plesiomorphic, eight per segment) or perichaetine (more than eight setae per segment).