Based on study of material collected in the Gambier Islands (eastern Polynesia) by the 1934 Mangarevan Expedition and in 1997, two endemic species of Euconulidae are shown to exhibit apertural barriers unlike those of any other Pacific island limacoids, both in their ontogeny and development. The barriers are fully developed only in juveniles and subadults and are resorbed in full-grown individuals. Aukena, hitherto considered a subgenus of the Hawaiian-Polynesian genus Hiona, is elevated to genus rank. Aukena endodonta, n. sp., with six apertural barriers (one columellar, three parietal, two palatal), is described, and A. tridentata (Baker, 1940) is redescribed. The natural environment of the Gambier Islands had already been severely altered by 1934, and the two endemic species of Aukena are considered extinct. One other endemic euconulid without apertural barriers, Pbilonesia mangarevae Baker, 1940, survives in a small patch of native forest at the base of Mount Mokoto.
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