The radiation of the Helicinidae in New Caledonia(Mollusca: Gastropoda: Neritopsina)including zoogeographic considerations

摘要

This study revises the land snail family Helicinidae in the biodiversity hot spot area of the island of New Caledonia and theadjacent Loyalty Islands (the political unit of New Caledonia). The investigation is primarily based on comprehensive collectionsassembled between 1978 and 1989 by scientists and collaborators of the Museum national d'Histoire naturelle, Paris. It encompassesabout 460 lots from over 240 stations and includes a considerable amount of alcohol preserved material. Nearly all relevant typematerial was relocated and is discussed and figured. In addition, certain historical collections (e.g., coll. Wagner, Warsaw andcoll. Dautzenberg, Brussels) were also studied. In the past, poor knowledge of the species has led to great confusions includingthe creation of numerous synonyms, rendering a proper identification of new material virtually impossible. Moreover, it did notallow any reliable assessment of the diversity, distribution patterns, ecological requirements, and zoogeographic affinities. Ofthe 31 nominal taxa proposed for New Caledonia, 14 species are presently recognised as valid, and three new species, Sturanyasublaevigatoides n. sp., S. houmacensis n. sp. and S. eutrochatelloides n. sp., are described. Species discrimination is based on shellcharacters with emphasis on microscopic surface structures that proved to be a valuable feature. For each species a descriptionof the embryonic shell, the teleoconch, internal shell structures, as well as the female reproductive system is provided. The recentmaterial allowed determination of distributions and habitat preferences and their correlations with environmental factors. Despiteproblems with intergrading characters among species, a key is presented to facilitate the use of the revision as an identificationtool for non-specialists, especially for the purposes of biodiversity inventory in the face of recent habitat destruction and speciesextinction. All New Caledonian helicinid species are endemics with more or less restricted distributions. The three LoyaltyIsland species are local endemics, while the smaller northern and southern islands adjacent to the main island (Iles Belep, Iledes Pins, etc.) share their one or two species with the main island. The highest diversity (eight species) is found in the southernthird of Grande Terre. Because of similarities in the female reproductive system all New Caledonian helicinids are included ina single genus, tentatively the Samoan genus Sturanya. The previous assignment to the Philippine genus Pleuropoma proveduntenable. Despite the similarities, two subgroups were recognised on Grande Terre that are readily distinguished by the surfacesculpture of the early postembryonic whorls. The significance of this character is evidenced by the resulting consistent patternof distribution of distinct northern and southern radiations, with the latter being more diverse and reaching further northbecause of the wider distribution of a number of small-sized species. Lacking similarly-detailed studies in neighbouring areas,zoogeographic affinities are difficult to discuss, but on account of superficial resemblance and the geological history of NewCaledonia, the Australian fauna is the most likely candidate for the origin of the main New Caledonian radiations. The youngerLoyalty Islands were clearly colonised from more than one source, with one species originating from the southern radiationon Grande Terre, while the other two species show affinities to Vanuatu and to several north-eastern archipelagos includingVanuatu, Fiji, Tonga and Samoa respectively.