RICHLING, I. (2009): The radiation of the Helicinidae in New Caledonia (Mollusca: Gastropoda: Neritopsina) including zoogeographic considerations. In: GRANDCOLAS, P. [ed.]: Zoologia Neocaledonica 7. Biodiversity studies in New Caledonia. - Mémoires du Muséum national d'Histoire naturelle 198: 247-372; Paris.
This study revises the land snail family Helicinidae in the biodiversity hot spot area of the island of New Caledonia and the adjacent Loyalty Islands (the political unit of New Caledonia). The investigation is primarily based on comprehensive collections assembled between 1978 and 1989 by scientists and collaborators of the Muséum national dHistoire naturelle, Paris. It encompasses about 460 lots from over 240 stations and includes a considerable amount of alcohol preserved material. Nearly all relevant type material was relocated and is discussed and figured. In addition, certain historical collections (e.g., coll. WAGNER, Warsaw and coll. DAUTZENBERG, Brussels) were also studied. In the past, poor knowledge of the species has led to great confusions including the creation of numerous synonyms, rendering a proper identification of new material virtually impossible. Moreover, it did not allow any reliable assessment of the diversity, distribution patterns, ecological requirements, and zoogeographic affinities. Of the 31 nominal taxa proposed for New Caledonia, 14 species are presently recognised as valid, and three new species, Sturanya sublaevigatoides n. sp., S. koumacensis n. sp. and S. eutrochatelloides n. sp., are described. Species discrimination is based on shell characters with emphasis on microscopic surface structures that proved to be a valuable feature. For each species a description of the embryonic shell, the teleoconch, internal shell structures, as well as the female reproductive system is provided. The recent material allowed determination of distributions and habitat preferences and their correlations with environmental factors. Despite problems with intergrading characters among species, a key is presented to facilitate the use of the revision as an identification tool for non-specialists, especially for the purposes of biodiversity inventory in the face of recent habitat destruction and species extinction. All New Caledonian helicinid species are endemics with more or less restricted distributions. The three Loyalty Island species are local endemics, while the smaller northern and southern islands adjacent to the main island (Îles Belep, Île des Pins, etc.) share their one or two species with the main island. The highest diversity (eight species) is found in the southern third of Grande Terre. Because of similarities in the female reproductive system all New Caledonian helicinids are included in a single genus, tentatively the Samoan genus Sturanya. The previous assignment to the Philippine genus Pleuropoma proved untenable. Despite the similarities, two subgroups were recognised on Grande Terre that are readily distinguished by the surface sculpture of the early postembryonic whorls. The significance of this character is evidenced by the resulting consistent pattern of distribution of distinct northern and southern radiations, with the latter being more diverse and reaching further north because 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 New Caledonia, the Australian fauna is the most likely candidate for the origin of the main New Caledonian radiations. The younger Loyalty Islands were clearly colonised from more than one source, with one species originating from the southern radiation on Grande Terre, while the other two species show affinities to Vanuatu and to several north-eastern archipelagos including Vanuatu, Fiji, Tonga and Samoa respectively.
© Ira Richling, Germany