Diversity of Helicinidae

Although already presented at the “Magnitude of molluscan diversity – the known and the unknown” Symposium held at the 78th meeting of the American Malacological
Society (2012), Ira Richling’s excellent paper on diversity of the Helicinidae was recently published (Richling, 2014).

Richling2014f2

Presenting a history of helicinid research starting in 1801 (the first taxon described was a Jamaican species), she has analysed the development of the diversity through time and also a number of revisions to compare the number of accepted (sub)species to available names. Under ‘Drawbacks in exploration’ several aspects (listed below in the abstract) are extensively discussed, which have an importance beyond the scope of the paper.

It would be interesting to explore these issues for other (large) land snail families in the (Neo)tropics. One of these issues is the “limited availability of wet preserved material”, which is quite crucial to make advances both in morphological and molecular studies. Unfortunately, the forthcoming implementation of the Nagoya Protocol (cf. Renner et al., 2012) makes things probably worse and opens up the possibilities for unwarranted claims from local scientists and license authorithies for financial expenditures, and more (examples are known of claimed co-authorship for several papers without any content contribution). Given the ongoing crisis in natural history museums, this is an avenue leading to disasters.

Richling2014f4

The full abstract of the paper reads: “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-Pacifi c 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”.

References:
Renner, S.C. et al., 2012. Import and export of biological samples from tropical countries—considerations and guidelines for research teams. – Organisms, Diversity & Evolution 12: 81–98.
Richling, I., 2014. Poorly explored jewels of the tropics: Estimating diversity in non-pulmonate land snails of the family Helicinidae (Gastropoda: Neritopsina). – American Malacological Bulletin 32: 246–258.

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