A Surprising Diversity of Aquatic Oligochaetes (Annelida: Clitellata) on Campbell Island/Motu Ihupuku (New Zealand), With a Checklist of Sub‐Antarctic and Antarctic Microdrile Oligochaetes

Campbell Island/Motu Ihupuku, 650 km SW of New Zealand, was surveyed for freshwater invertebrates during the austral summer of 2010/11 as part of the Campbell Island Bicentennial Expedition. Aquatic oligochaetes constituted a considerable proportion of the species collected. A total of 19 species were recorded, including 6 Naididae, 9 Enchytraeidae, and 4 Phreodrilidae, bringing the total number of microdrile species known from freshwater habitats on the island to 20. At least nine are known only from this island. Two new genera and four new species are described, with other specimens also likely representing undescribed species. The island's fauna has biogeographic affinities with other islands in the Southern Ocean/sub‐Antarctic and high latitude regions of southern continents, such as Macquaridrilus (also from Macquarie Island), Biprostatus (also from Tasmania) and Phreodrilidae which primarily inhabits Gondwanan landmasses and southern oceanic islands. Several species are likely human introductions. Species richness on Campbell Island greatly exceeds that of Macquarie Island, where only six species have been documented. Interpretation of the origins of this diversity and comparisons with other islands is hampered by inadequate knowledge of worm faunas from other islands and even from high latitude regions of some southern hemisphere continents.