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Tuhinga 21: 161-252
ABSTRACT: The prehistoric (pre-AD1800) landsnail fauna of the Rarotongan coastal plain comprised at least 43 species. Seventeen of these were probably endemic to this island; the remainder of the fauna consisted of species with wider distributions in the tropical Pacific, including several species probably introduced by Polynesians. By contrast, the modern coastal landsnail fauna as surveyed in 2005–07 contained 48 species and was dominated by non-indigenous species that were mostly introduced to Rarotonga in the last 100 years or so; most of the Rarotongan and Cook Island endemics are either extinct or verging on extinction. Loss and modification of native shrubland and forest habitats in the lowlands during the historic period was undoubtedly a key factor in the declines and extinctions of many native Rarotongan snail species. However, the introduction and establishment of a suite of non-indigenous predators during the historic period was probably also a significant contributing factor, and is inferred to have been the main cause of the declines and extinctions of native snail species in inland Rarotonga over the last 140 years. Descriptions of 13 new species of landsnails, thought to be endemic to Rarotonga, are given: Atropis rarotongana n.sp.(Assimineidae); eight species of Minidonta (Endodontidae) – Minidonta aroa n.sp., Minidonta arorangi n.sp., Minidonta iota n.sp., Minidonta kavera n.sp., Minidonta matavera n.sp., Minidonta ngatangiia n.sp., Minidonta pue n.sp. and Minidonta rutaki n.sp.; and four species of Sinployea (Charopidae) – Sinployea muri n.sp., Sinployea taipara n.sp., Sinployea titikaveka n.sp. and Sinployea tupapa n.sp. Nesopupa rarotonga n.sp. (Vertiginidae) from the southern Cook Islands is also described.
KEYWORDS: Pacific Ocean, Cook Islands, Rarotonga, landsnail, fauna, new species, fossil species, endemic species, non-indigenous species, extinctions, Holocene faunal changes.