Helodrilus hachiojii sp. nov. (Oligochaeta: Lumbricidae) from Japan

Abstract

A small (60-70mm) semi-aquatic or limnic lumbricid earthworm from a creek in Hachioji, western Tokyo appears new to science and is named after the locality. It is tentatively attributed to the genus Helodrilus Hoffmeister, 1845 – characterized by lack of nephridial bladders – rather than Eisenia Malm, 1877 that holds the only other endemic lumbricid, E. japonica (Michaelsen, 1891). The current species is close to type Helodrilus oculatus Hoffmeister, 1845 but differs on its clitellum in segments 23-31 with tubercula pubertatis in 29, seminal vesicles in 9-12, and intramural calciferous glands in 11-12 extending into 13-14. Further lack of spermathecae is distinctive, whereas He. oculatus is not known for parthenogenesis in its European headquarters. Restricted distribution suggests endemicity, however discovery of a specimen in a rice paddy at Lake Biwa indicates at least partial transportation. Alternatively, its apparent rarity and restriction may relate to common sampling omission of small species.