Symposium on the "Magnitude of molluscan diversity - the known and the unknown"

The symposium formed part of the 78 Annual Meeting of the American Malacological Society in Cherry Hill, New Jersey, and was held on 19 and 20 June 2012. While everyone talks about biodiversity we asked the basic question: What do we know about molluscan diversity? Or even more simply: How many species of molluscs exist today? A simple question to ask but diffi cult to answer. Of course, this question is not a new one, but ever rising threats to our environment and thus, habitats of molluscs render it more urgent than ever to know what lives on our earth and what will we lose. Land and freshwater molluscs are among the most endangered groups worldwide (Lydeard et al. 2004, Regnier et al. 2009). More recent comprehensive estimates of molluscan diversity suggest the number of described species at 31,000 non-marine and 52,500 marine, but the number of yet unknown diversity may be roughly one third to more than an equal amount (Lydeard et al. 2004, Bouchet 2006). The symposium title refl ects these two aspects while the “known” refers to described species rather than implies that their number is known considering the often unknown share of synonyms among available names. The goal of the symposium was to gather new data to narrow down a realistic estimate of the diversity of this second largest phylum in the animal kingdom and to reveal the progress made during the last few years. The 22 talks presented in Cherry Hill encompassed studies on special taxonomic groups, geographic areas as well as theoretical approaches like analyzing saturation curves, the portion of valid species versus synonyms, correlation to rarity, sampling methods, the amount of undescribed species in collections versus discovery by new fi eldwork, and last but not least elucidated the potential of new methods. The “unknown” stood for what remains to be discovered in terms of species not yet found in underexplored habitats and regions, species not yet recognized due to the lack of taxonomic expertise, revisionary works, and cryptic species. If the title was mirrored in two talks, Gary Rosenberg’s analyses of databases reducing the estimated diversity of described species to 70,000–76,000 represented the “known“ (this issue) while Philippe Bouchet certainly took the audience to the frontier of the “unknown“. Based on his tremendous exploration efforts in the tropical Indo-Pacifi c Bouchet assumed that only 30% of the molluscan diversity of this area is known. This already anticipates that despite some detailed approaches the latter aspect remains not only as undescribed diversity but still unknown in its extent. In terms of marine species, Rudiger Bieler questioned our knowledge of the molluscan fauna in the well known Florida Keys. Philippe Bouchet, as mentioned above, characterized the tropical Indo-Pacifi c as a treasure trove for new species and highlighted the phenomenon of a high percentage of species occurring in low abundances. Janet Voight evaluated the exploration of hydrothermal vent habitats (this issue). John Taylor, co-authored by Emily Glover, gave insight into the enormous diversifi cation of Lucinidae triggered by their obligate chemosymbiosis. Continuing with bivalves, Paul Valentich-Scott dug deep into the hyperdiverse group of Galeommatoidea which not only amaze us with their previously unexpected species diversity but even more by their range of unusual lifestyles. Patrick LaFollette described the attempt to catalogue the published taxa of the megadiverse family Pyramidellidae resulting in an estimated 10,000 names regardless of status. James McLean’s review of the Liotiidae and Areneidae more than doubles the known diversity and sampling still seems far from complete. Exposing the most cryptic groups, Timea Neusser and colleagues gave insights into the mesopsammic fauna and their underestimated diversity and ability to colonize unusual habitats (this issue, Jorger et al.). Moving from the least known to the best known, Fabio Moretzsohn reviewed the progress of cataloging the Cypraeidae (this issue). An equally attractive group but less popular among shell collectors, Terrence Gosliner described nudibranch exploration. Greatly supported by citizen scientists like scuba divers, Gosliner feels their role is not only in accelerating the discovery of new species but also in helping to monitor environmental changes. The contributions focusing on advances by the application of molecular techniques identifi ed signifi cant numbers of so-called cryptic species: Ellen Strong estimated the diversity of Cerithiidae two to three times higher than currently recognized. John Slapcinsky deduced equal ranges from his analyses of the land snail genera Tropidophora and Daedolochila (this issue, on Tropidophora). To the relief of less wellequipped biologists both pointed out that after recognizing the hidden species differentiating morphological characters Stuttgart State Museum of Natural History, Rosenstein 1, 70191 Stuttgart, Germany