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1 September 2014 Poorly Explored Jewels of the Tropics: Estimating Diversity in Non-Pulmonate Land Snails of the Family Helicinidae (Gastropoda: Neritopsina)
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Abstract

Helicinids represent a family of tropical land snails with a distribution range limited to the subtropical and tropical zones of the New World, Australasia, and the Pacific. For an estimate of diversity in this poorly systematically revised group, the total number of described taxa was determined and used for calculations based on analyses of selected case studies with regard to the percentage of valid and new taxa.

Extensive bibliographic searches identified about 1,250 available names, regardless of rank, that were described from 1801 onward. Fiftyeight percent of the names represent New World taxa whose majority (63%) was created before 1880 while the intensive study in most of the Australasian and Pacific areas started much later with the bulk of taxa described between 1880–1930. An analysis of the distribution of the type localities and the times of descriptions allowed for identification of scarcely- and well-studied areas.

Eight potentially representative case studies of major revisions were compared with respect to changes in described versus “true” diversity. The geographic range covered Costa Rica, Cuba, Jamaica, Lesser Antilles, New Caledonia, northeast Australia, and the Hawaiian and Gambier Islands. In these studies approximately half of the available names were regarded as synonyms (range from 37 to 72%). On the other hand, 36 to 41% of the recognized diversity represented new species depending on whether a more lumping or splitting approach was considered, the latter simulated by simply counting subspecies as equal units of diversity. The amount of new taxa ranged from 2% (Cuba) to 90% (Gambier Islands). Under the assumption that six of the studies were representative throughout the area of distribution, worldwide diversity would range from 770 to 1,140 species or up to 1,400 species if the studies from the Australasian-Pacific area were realistic. Although obviously poorly studied, in comparison with an estimate for all continental molluscs of Mexico and Central America by Thompson (2011), helicinids would still be among the better documented snail families for this region.

The following aspects and their consequences are discussed as most significant drawbacks in the exploration of helicinids: questionable systematic concepts above species level; limited recognized differentiating characters and convergence; species complexes and last, massive habitat loss, increasingly fragmented distribution and extinction. Another practical aspect is the rather limited availability of wet preserved material.

Ira Richling "Poorly Explored Jewels of the Tropics: Estimating Diversity in Non-Pulmonate Land Snails of the Family Helicinidae (Gastropoda: Neritopsina)," American Malacological Bulletin 32(2), (1 September 2014). https://doi.org/10.4003/006.032.0216
Received: 20 February 2014; Accepted: 1 April 2014; Published: 1 September 2014
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