Evolutionary biology is not only a biological subdiscipline but also a synthetic theory based on comprehensive scientific achievements. However, to date biodiversity, which is far from being fully documented, and the evolutionary processes leading to it are two of the least understood phenomena in evolutionary biology. Surprisingly, decades after the Modern Synthesis and centuries after the commencement of research in biological systematics, we are still unable to satisfyingly answer apparently simple yet fundamental questions. Here termed “Darwinian mysteries”, these are for example, how many species inhabit Earth today, what are species, where are they distributed, and how did biodiversity originate. While many contributions in malacology center around morphology, anatomy, and phylogenetic relationships within and among constituent taxa, molluscs only rarely have been utilized explicitly as models for the study of general aspects in evolutionary biology. However, this particular group, with its many features and facets, is highly suitable for providing fundamental insights into the mechanisms that generate biodiversity, pattern in historical biogeography, and the underlying processes of speciation and radiation. Here, I discuss some aspects of these fundamental questions that are of relevance for evolutionary biology, hoping that the influence of malacology within evolutionary biology will increase in the future.

Biologists have used a wide range of organisms to study the origin of taxa and their subsequent evolutionary change in space and time. One commonly used tool is the molecular clock approach, relating substitution rates of nucleotide or amino acid sequences to divergence times. The accuracy of the molecular clock, however, has long been subject to controversy, and numerous papers have addressed problems associated with estimating divergence times. Some workers pointed out a striking imbalance between sophisticated software algorithms used for molecular clock analyses on the one hand, and the poor data on the other hand. Moreover, there is often unease among workers relative to molecular clocks because of the controversy surrounding the approach, the complex mathematical background of many molecular clock tools, the still limited number of available, user-friendly software packages, the often confusing terminology of molecular clock approaches, and the general lack of reliable calibration points and/or external clock rates. The current review therefore briefly provides an overview of analytical strategies, covering approaches based on calibration points and/or bounds, approaches based on external clock rates, and approaches that attempt to estimate relative divergence times in the absence of information that can be used for estimating substitution rates. It also deals with major problems and pitfalls associated with data and analyses, including potential errors of calibration points and bounds, the performance of the gene(s) used, estimation of confidence limits, and misinterpretation of the results of clock analyses due to problems with sampling design. A substantial part of the review addresses the question of “universal” molecular clock rates and summarizes important biological and life history variables that account for deviations from rate constancy both between lineages and at different times within lineages. The usefulness of these factors is discussed within the framework of “trait-specific” molecular clock rates. One such clock rate is introduced here for the cytochrome c oxidase subunit I (COI) gene in small dioecious, tropical and subtropical Protostomia with a generation time of approximately one year. A flow chart is provided as a “simple fool's guide” to molecular clock analyses, together with a glossary of widely used terms in molecular clock approaches. Finally, step-by-step examples are provided for calculating divergence times in the caenogastropod subfamily Pyrgulinae based on both an internal calibration point and a “trait-specific” molecular clock rate, and it is demonstrated how a relative clock approach can be used for testing evolutionary hypotheses. Our review encourages a judicious use of molecular clock analyses in evolutionary studies of invertebrates by demonstrating their great potential on the one hand and (often-manageable) problems and pitfalls on the other hand.

Molluscs constitute the second largest phylum in terms of the number of described species and possess a wide array of characteristics and adaptations for living in marine, terrestrial, and freshwater habitats. They are morphologically diverse and appear in the fossil record as far back as the early Cambrian (∼560 mybp). Despite their high diversity and long evolutionary history, molluscs are often underused as models for the study of general aspects of evolutionary biology. Freshwater snails in the family Ampullariidae have a global tropical and subtropical distribution and high diversity with more than 150 species in nine currently recognized genera, making them an ideal group to address questions of historical biogeography and some of the underlying mechanisms of speciation. They exhibit a wide range of morphological, behavioral, and physiological adaptations that have probably played a role in the processes of diversification. Here we review some of the salient aspects of ampullariid evolution and present some early results from ongoing research in order to illustrate the excellent opportunity that this group provides as a system for addressing numerous questions in evolutionary biology, particularly with regard to the generation of biodiversity and its distribution around the globe. Specifically, we suggest that ampullariids have great potential to inform (1) biogeography, both on a global scale and a smaller intra-continental scale, (2) speciation and the generation of biodiversity, through analysis of trophic relations and habitat partitioning, and addressing issues such as Rapoport's Rule and the latitudinal biodiversity gradient, and (3) the evolution of physiological and behavioral adaptations. Also, a number of species in the family have become highly successful invasives, providing unintentional experiments that may offer insights into rapid evolutionary changes that often accompany introductions, as well as illuminating invasion biology in general.

Oceanic islands have long been important in evolutionary biology. Land snails are a major component of oceanic island biotas and have much to offer as systems for addressing major questions in evolution and biogeography. We review patterns of within-archipelago biogeography and diversification in two large Hawaiian land snail groups, the Succineidae and the Achatinellinae. Molecular studies suggest that long-distance oceanic dispersal and colonization of the Hawaiian Islands has been rare but between-island dispersal has been far more common. Long-distance oceanic dispersal is the most important driver for deep phylogenetic divergence. Dispersal is also important within the archipelago, while among-island vicariant processes result in only a portion of tip clade diversity. The Achatinellinae are monophyletic but there is evidence of a deep phylogenetic split between the two Hawaiian succineid clades, a result of two independent colonizations reflecting two oceanic dispersal events. Hawaiian succineids have also dispersed to Samoa and Tahiti. Dispersal is an important biogeographical phenomenon, and its role in shaping distributions of island lineages should not be underestimated. Because of their relatively sedentary nature, yet a proclivity for long-distance passive dispersal, island snails can facilitate insights into mechanisms of evolutionary diversification. Important phylogenetic lessons are emerging from studies of island snails and such studies will eventually allow estimation of ages of species groups, speciation rates, timing of the processes involved in community assembly, and other dynamics, all of which are important contributions to the overall understanding of evolution.

We reconstructed the molecular phylogeny of 78 specimens, including nearly all nominal species of the genus Pyrenaearia, and discussed the implications of the molecular phylogeny for species delimitation. The four basal clades obtained by mitochondrial COI and 16S sequences were highly congruent with nuclear ITS markers, shell morphology, and geographic distribution patterns, and were considered different species under the phylogenetic species concept: Pyrenaearia carascalopsis (Bourguignat in Fagot, 1884), P. carascalensis (Férussac, 1821), P. parva Ortiz de Zárate, 1956, and P. cantabrica (Hidalgo, 1873). Evidence of reproductive isolation between coexisting species of these basal clades has also been obtained. Because of genetic divergence, together with peculiarities of habitat use, distributional range, and shell morphology, P. organiaca (Fagot, 1905) and P. navasi (Fagot, 1907) were regarded as valid species. Further subdivisions within Pyrenaearia were also considered. Some incongruencies were found between shell morphology and DNA-based taxonomy, including the presence of hairs in adult shells and shell shape adaptations to different altitudes. The deepest split in Pyrenaearia involves four different lineages and represents an ancient event, occurring during the Pleistocene or even the Pliocene. Subsequent Pyrenaearia speciation within the four main groups has been a very recent process, and it is hypothesized to have occurred during Pleistocene cycles of climatic cooling and warming. Chronologically, a third speciation process is occurring from the Würm de-glaciation to the present time. All these processes included allopatric speciation of the high-altitude taxa during warmer interglacial periods, but parapatric or peripatric speciation events could also be involved. Based on the present day distribution of the species and their different altitudinal preferences, the whole genus could constitute a good model to investigate the evolutionary processes that created this diversity. It could also be an excellent group of closely related taxa for the study of the effect of PlioPleistocene climate changes on species distribution, population structure, speciation processes, secondary contacts, and passive dispersal.

Long-lived lakes with their often in situ evolved faunas form an excellent model system to study evolution. The paleontological record of long-lived lakes provides possibilities to investigate the tempo and mode of evolutionary change. However, in order to demonstrate such processes, a combined rigorous temporal and spatial framework is needed in order to make sure (1) alleged evolutionary successive morphs are not misidentified immigrant species and (2) morphological variation is not due to ecophenotypy. Other factors that may cause the development of discrete morphs, such as sexual dimorphism, also must be considered. In this paper, evolution in the Miocene snail genus Toxosoma Conrad, 1874 from long-lived Lake Pebas in western Amazonia is studied within such a temporal and paleo-environmental framework.

Chitons are often referred to as “living fossils” in part because they are proposed as one of the earliest-diverging groups of living molluscs, but also because the gross morphology of the polyplacophoran shell has been conserved for hundreds of millions of years. As such, the analysis of evolution and radiation within polyplacophorans is of considerable interest not only for resolving the shape of pan-molluscan phylogeny but also as model organisms for the study of character evolution. This study presents a new, rigorous cladistic analysis of the morphological characters used in taxonomic descriptions for chitons in the living suborder Lepidopleurina Thiele, 1910 (the earliest-derived living group of chitons). Shell-based characters alone entirely fail to recover any recognized subdivisions within the group, which may raise serious questions about the application of fossil data (from isolated shell valves). New analysis including characters from girdle armature and gill arrangements recovers some genera within the group but also points to the lack of monophyly within the main genus Leptochiton Gray, 1847. Additional characters from molecular data and soft anatomy, used in combination, are clearly needed to resolve questions of chiton relationships. However, the data sets currently available already provide interesting insights into the analytical power of traditional morphology as well as some knowledge about the early evolution and radiation of this group.

First introduced by Ernst Haeckel in the nineteenth century, the use of developmental sequences has recently seen a renaissance as part of the study of the evolutionary biology of embryos; here we review briefly the literature describing gastropod developmental sequences, appraising the extent to which it has contributed to this renaissance. Gastropods have figured extensively in studies of early development with cell lineage analysis available for numerous taxa. Phylogenetic comparisons of these data reveal strong evolutionary signals, particularly in relation to early cell divisions. In contrast, although the description of post cell division developmental stages, including functional elements of development, in gastropods is extensive, interspecific comparisons are rare and tend to focus instead on developmental mode. However, a recent comparison of the sequence of functional and morphological events in a clade of basommatophoran snails demonstrated several alterations in the timing of developmental events (i.e., heterochronies) across the phylogeny. Many gastropod groups may offer the potential to carry out similar investigations of the evolutionary importance of sequence heterochrony and to try to unravel the mechanistic basis for such patterns in developmental sequences.

In 2002, the U.S. Department of Agriculture requested assistance from the American Malacological Society in the development of a list of non-native snails and slugs of top national quarantine significance. From a review of the major pest snail and slug literature, together with our own experience, we developed a preliminary list of gastropod species displaying significant potential to damage natural ecosystems or agriculture, or human health or commerce, and either entirely absent from the United States to our knowledge or restricted to narrow areas of introduction. Comments on the list from the worldwide malacological community were then solicited and led us to modify the original list. We then evaluated the taxa on this list by ranking them according to 12 attributes—seven biological variables and five aspects of human interaction—based on thorough review of the detailed literature. The ranked list that emerged from this risk assessment process included 46 taxa (species or species-groups) in 18 families. The highest ranked taxa were in the Ampullariidae, Hygromiidae, Cochlicellidae, Helicidae, Veronicellidae, Succineidae, Achatinidae, and Planorbidae. We validated the risk assessment model by scoring a suite of non-native snail and slug species already present in the United States. The list is not definitive but rather is offered as a framework for additional research. There remain important gaps in biological knowledge of many of the taxa evaluated, and rigorous reporting of economic impacts is extremely limited. We expect the prioritizing and listing of taxa to be dynamic, not only as these knowledge gaps are filled but also as environmental, agricultural, international trade, and societal factors change.

During environmental characterization of the Campos Basin, Rio de Janeiro State (22°S), about 120 samples from depths between 400 and 2000 m were dredged with a 0.25-m² box-core, and a high biodiversity of micro-molluscs was found. Although only dead animals were collected, the shells were often in a good state of preservation. Six new species, belonging to gastropods families Aclididae (Aclis kanela n. sp.), Trochidae (Mirachelus urueuauau n. sp. and Calliotropis pataxo n. sp.), Skeneidae (Palazzia pankakare n. sp. and Adeuomphalus xerente n. sp.), and Tornidae (Ponderinella xacriaba n. sp.) are described.

Eight species of Cuspidariidae belonging to the genera Myonera Dall, 1886, Octoporia Scarlato and Starobogatov, 1983, and Protocuspidaria Allen and Morgan, 1981 were obtained in samples from the continental slope (700-2000 m depth) at Campos Basin, Rio de Janeiro state (22°S), Brazil. Myonera paucistriata Dall, 1886 and Protocuspidaria verityi Allen and Morgan, 1981 are now documented from the Campos Basin. Though previously reported for Brazil, the known range of Octoporia octaporosa (Allen and Morgan, 1981) is enlarged southward. Myonera limatula (Dall, 1881) and Protocuspidaria atlantica Allen and Morgan, 1981 are reported from the South Atlantic Ocean for the first time. Myonera kaiwa sp., nov. and Protocuspidaria jarauara sp. nov. are described herein. Myonera sp., an eighth taxon, is present as one unique specimen. The presence of micro-pits on the shell surface is reported for the first time in the Septibranchia.

X-ray Quantitative Texture Analysis (QTA) results are examined for the outer aragonitic shell layers of Helix aspersa aspersa (Müller, 1774) to probe the relevance of the approach to non-flat surfaces. Two sets of H. aspersa aspersa were studied, for a total of 29 samples. Quantitative texture analysis showed that although the nature of the texture present was roughly constant, the textural strength varied significantly among specimens because of biologically inherited surface irregularities. A statistical analysis showed that textural strength exhibited larger standard deviations for snails selected for greater shell weight than for control snails. The H. aspersa aspersa aragonite texture is the same as observed in previous studies, with <110> shell growth directions. This texture causes elastic behavior of the mineral part of the shell, which accommodates moderate shear and compression. We furthermore determine that the colored bands at the shell surface were aligned with the <020> crystal directions.

The Bruneau River in southwestern Idaho is a largely free-flowing desert stream characterized by a snowmelt-driven hydrograph, flash floods, and geothermal inputs. We surveyed the lower Bruneau River from its confluence with the Snake River upstream to Hot Creek, a distance of approx. 41 river kilometers, between 1997 and 2008. We supplemented our work with a review of collections held at the Orma J. Smith Museum of Natural History, College of Idaho and with collections available online from national and international museums. The known mollusc fauna consists of 18 species (11 gastropods and 7 bivalves) from eight families. Molluscan richness is greatest in free-flowing stream reaches and is dominated by hydrobiid and unionid taxa.

We examine the morphometric, chemical, and physical properties of adult shells from breeding populations of Cornu aspersum maxima (Taylor, 1883), Cornu aspersum aspersum (Müller, 1774), and Helix pomatia (Linnaeus, 1758). The higher thermal requirements of the African subspecies C. aspersum maxima were confirmed by the fact that normal shell maturation, indicated by a decreasing calcium content as the snail ages, was related to an increased mean air temperature of over 22.9 °C during the breeding season. In contrast, normal shell maturation of the European subspecies C. aspersum aspersum occurred with a temperature in the range of 20.6–23.6 °C. Based on the results of texturometric analysis, shell puncture force increased with an increase in temperature during breeding. In contrast, shell puncture force decreased and collapsing force increased with increasing relative humidity. The mechanical strength of C. aspersum and H. pomatia shells was related to their chemical composition and the level of their structural maturity. Shells containing a higher percentage of calcium were characterized by lower mechanical strength than those containing a lower amount.

In December 2008, eight sacoglossan specimens of Hermaea Lovén, 1844 were collected from uniseriate red algae (cf. Wrangelia tanegana) at two sites on the west coast of Okinawa, Japan. These specimens are compared to the described Aplysiopsis wrangeliae Ichikawa, 1993 from Okinawa which we and other authors have previously suggested belongs to the genus Hermaea; we suggest that our specimens are attributable to Hermaea wrangeliae (Ichikawa, 1993).