Mollusks are megadiverse
The Mollusca, as second largest animal phylum, contribute with countless fossil and roughly 100,000 Recent species, and many more remain to be discovered and investigated. In whichever tropical, temperate or polar ocean we have collected mollusks during the last 10 years, we always made new discoveries. Depending on the region, 10-50% of species collected referred to species new to science. Regarding gastropod species, 80% or even more may be new when exploring abyssal depths of the oceans (Schrödl et al. 2010). Usually, species with individuals growing large, having massive shells and looking conspicuous are better represented in faunal lists than small and colorless, sluggish specimens living hidden between sand grains or parasitic in deep sea host animals. During centuries, molluscan taxonomy largely depended on shell morphology, and more recently also gross anatomy and radula features were compared and considered. Yet, the renaissance of (micro)morphology and especially the advent of molecular genetics greatly supplemented and enriched molluscan taxonomy and diversity research. There is increasing evidence that cryptic species, i.e. those not detectable by traditional methods, will boost the species richness in several sea slug groups. An exciting range of traditional and novel methods and tools is available to explore the hidden species diversity in molluscs, and also their morphological, functional and genetic diversity, i.e. any kinds of biological diversity. Ultimately, we are interested in how and why such an overwhelming organismic diversity evolved. Modern phylogenetic and evolutionary research provides exciting new insights into the secrets of molluscan life history.