A new gigantic earthworm of the genus Metaphire Sims and Easton (Megascolecidae: Oligochaeta) from Taiwan with reference to evolutional trends in body sizes and segment numbers of the Pheretima genus-group

This paper describes a new species of gigantic terrestrial earthworm Metaphire taiwanensis sp. nov. from western Taiwan. It reached the maximum length of 860 mm for a living clitellate and 637 mm after preservation. It is an autochthonous species found in Mt Beidongyan and the Meifeng area of the Central Mountain Range at elevations of 1800-2100m. M. taiwanensis is octothecate and protandric, characters shared by Metaphire stephensoni (Michaelsen) of Indochina, and Metaphire bununa Tsai, Tsai and Liaw and Metaphire paiwanna Tsai, Tsai and Liaw of Taiwan. These four species are combined as a new speciesgroup called the stephensoni-group within the genus Metaphire Sims and Easton. It is closely related to the congeneric ignobilis species-group, which is also octothecate but holandric. It differs from holandric and quadrithecate Metaphire magna (Chen) of Hainan Island, in which the length also reaches 700 mm. Specific variation and evolutionary trends in sizes and segment numbers of the Pheretima genus-group are discussed.