The Accanthodrile earthworm genus Microscolex (Diplotrema) (Megascolecidae : Oligochaeta) in the Northern Territory of Australia

Diplotrema is redefined to include Australian species formerly assigned to the subgenus Microscolex (Notiodvilus) and thus now contains species with or without spermathecal genital setae, presence of which formerly was considered diagnostic of Diplotrema. The presence of similar spermathecal setae in the related North American genus Diplocardia is noted. Nine species of Diplotrema are described from the Northern Territory, of which eight are new, and a key to these species is provided. One of these, D. ridei, sp. nov., has a subspecies on Melville I. the first report of an insular subspecies of a mainland oligochaete species for Australia. Three species-groups are tentatively recognized for the species of the Northern Territory. New taxonomic notes are given for D. australis, D. dameli, D. fragilis, D. queenslandica and D. cornigravei, species occurring outside the Territory. It is suggested that Diplotrema is a relict of a Gondwanaland acanthodrile fauna.