Preliminary review of 130 available genus-group names for the notoriously polyphyletic group of skeneiform microgastropods has revealed a concentration of biodiversity in Australasia, primarily on the shelf and on or in clastic substrates. Forty-four of the names are based on type species from Australia or New Zealand, and some of the most speciose genera are abundantly represented and well preserved in the Cenozoic fossil record. Many skeneiform species were not illustrated at the time of description, and remain unillustrated except by inadequate line drawings. Features observed in scanning electron micrographs are used to define a set of new shell characters and to name and diagnose a new vetigastropod family Crosseolidae. Diagnostic features are the shallow anterior canal at the base of the columellar lip, a prominent umbilical keel, and a pseudumbilicus between the umbilical keel and the sharply defined inner lip. The shell of the type species of Crosseola, C. concinna (Angas, 1868), is illustrated with SEM for the first time, along with variation in shells of Crosseola striata (Watson, 1883). Three additional genera are assigned to the family: Conjectura Finlay, 1927, Conradia A. Adams, 1860, and Crossea A. Adams, 1865. Dolicrossea Iredale, 1924 is excluded on external anatomical evidence that the type species is a rissooidean caenogastropod. Intraspecific variation in crosseolids is partly a consequence of terminal growth features: adult variciform thickening of the outer lip, descending suture, and modifications of the columella and umbilical region. A restrictive definition of Skeneidae is provided along with examples of Australasian genera that can be allocated confidently to other families. Three predominantly Australasian groups of Cenozoic skeneiform taxa are identified for intensified study and potential allocation to new families. The constituency of vetigastropod family-groups and inferences of their relationships are too poorly resolved at this time to warrant the use of superfamily names.

The invasion of the bryozoan Membranipora membranacea to the Gulf of Maine in 1987 eventually provided an additional prey resource to the dorid nudibranch Onchidoris muricata (Müller, 1776). The impact of this novel prey on the population and reproductive biology of O. muricata was investigated at an intertidal site in the southern Gulf of Maine from January 2005 to October 2009. Nudibranchs were found associated with a variety of bryozoans, with a seasonal shift from Electra pilosa (December to May) to M. membranacea (June to November). Juveniles (< 3 mm) were found in all months except May, June, and July and mature nudibranchs were present in all months. Copulating pairs were observed between lanuary and July and spawn masses were found between March and September on the undersides of rocks usually attached to the surface of bryozoans. The population structure and reproductive phenology of O. muricata at this intertidal site shows changes from historical reports. Whether adaptive change of this native predator to invasive prey species is occurring remains a possibility and emphasizes the need for long-term studies documenting native predators and invasive prey for possible changes in species interactions.

Species of the genus Elysia Risso, 1818 have relatively few external characters useful for species identification, and features such as papillae and/or color markings on the body surface are often used to classify and identify species. Elysia atroviridis Baba, 1955 and E. setoensis Hamatani, 1968, for example, have been described as distinct based mainly on such characters. Close examinations of 46 specimens identifiable as either species collected from nine localities in Japan revealed that many specimens exhibited mixed features of the two species. Detailed comparisons of radular morphology could also not differentiate the two species. With phylogenetic analyses based on COI and 16S rRNA (1072 bp in total), all of the examined specimens formed a single clade with very little variation among specimens. The AMOVA of the specimen haplotypes showed there was no significant genetic differentiation in relation to differences in external morphology, geographic region, or algal host. Our results indicate that E. atroviridis and E. setoensis are conspecific. In contrast, cryptic species were found in two other clades of congeners, indicating that further taxonomic scrutiny is needed within the genus.

The best way to reduce problems related to invasive species is by preventing introductions into potentially susceptible areas. The purpose of this study was to create distribution models for the invasive gastropod Achatina fulica Bowdich, 1822 in South America in order to evaluate its potential geographic distribution and identify areas at potential risk. This mollusc, considered one of the 100 world's worst invasive alien species, is the focus of intense concern due to its impact on agriculture, human health, and native fauna. We tested two commonly used ecological niche modeling methods: Genetic Algorithm for Rule-Set Prediction (GARP) and Maximum Entropy (MaxEnt). Models were run with occurrence points obtained from several sources, including the scientific literature, international databases, governmental reports and newspapers, WorldClim bioclimatic variables, and altitude. Models were evaluated with the threshold-independent Receiver Operating Characteristic (ROC) and Area Under the Curve (AUC). Both models had consistent performances with similar areas predicted as susceptible, including areas already affected and new potentially susceptible areas in both tropical and temperate regions of South America.

We examined whether the terrestrial micro snail Vallonia excentrica Sterki, 1893 detects and follows conspecific mucous trails. A trail-layer snail moved on a transparent 5×5 cm plastic sheet to establish a mucous trail then was removed. A trail-follower snail of the same species was allowed to move on the same plastic sheet. Of 30 trials, 24 trail-followers encountered the laid trail. We compared with null models the distance that the trail-follower trail was coincident with the laid trail, and the turning angle of the trail-follower trail upon meeting the laid trail, to determine that V. excentrica follows conspecific mucous trails more, and showed sharper turning angles upon meeting a trail, than expected by the null model.

A new species of the helminthoglyptid genus Cahuillus Roth, 1996 from the Mojave Desert of southeastern California, is described as Cahuillus fultoni n.sp. It lacks the dart sac and associated mucus glands of the female system found in all other members of Cahuillus including Eremarionta rowelli unifasciata (Willett, 1930), which is herein reassigned to this genus and elevated to species status as Cahuillus unifasciata. Sequence comparisons support the new species as distinct from other available taxa, based on combined analysis of 16S and COI mitochondrial gene regions for Cahuillus fultoni and four of the nominal taxa of Cahuillus or Eremarionta Pilsbry, 1913 within the Mojave. Although a relevant species, Cahuillus greggi (Miller, 1981), remains unsampled, the estimated phylogeny supports a sister species relationship between C. unifasciata and C. fultoni.

The polyplacophoran Chiton articulatus Sowerby, 1832, is distributed along the tropical Pacific coast of Mexico and has been collected for generations in an artisanal manner for bait or as a complement in domestic cookery of coastal inhabitants; nevertheless, recently, some restaurants are offering this chiton to the tourists as a gourmet and aphrodisiac food, thus becoming of potential economic interest. This study explores in a population of C. articulatus adults from Oaxaca, southern Mexican Pacific, the changes in morphometry and in somatic and reproductive indices throughout one year, reporting on five reproductive indices, five somatic indices, body shape (BS), and length-weight relationships. An attempt is made to elucidate the energetic trade-off between somatic and reproductive tissues, including an assessment of whether these can be estimated from noninvasive indices. Somatic indices diminished considerably as gonad development proceeded, thus showing an inverse relationship with reproductive indices. Body mass index (BMI, i. e., physical conditions) patterns revealed that chitons were overweight (in the sense of high accumulation of lipids in the gonad) during reproductive seasons. The C. articulatus body was mainly oval-shaped throughout the whole sampling period. The slope of the length-weight regressions indicated an allometric growth (b, between 2.2 and 2.8). Gonad development is fueled by energy and nutrients derived from food rather than from reallocation of somatic reserves, although some somatic tissue constituents (in particular from foot) of reproducing adults may be mobilized in the short-term to meet nutrient and energy needs for reproduction. Reproductive seasons of C. articulatus according to the measured indices, occurred around May (late-spring) and again around August-September (late-summer), and these periods were correlated with maximum sea surface temperatures. The measurement of BS together with BMI can be used nearly as effectively as the more invasive reproductive indices to estimate reproductive seasonality.

The genus Lyonsia Turton, 1822 is represented in the southwestern Atlantic Ocean by three species: Lyonsia hyalina (Conrad, 1831), which is very common on the east coast of the U.S.A. and has a few isolated records from Brazil and Uruguay; Lyonsia malvinensis d'Orbigny, 1846, known only from the Falkland (Malvinas) Islands; and Lyonsia alvarezii d'Orbigny, 1846, restricted to southern Brazil, Uruguay and Argentina. Some authors consider L. alvarezii a synonym of L. hyalina. Study of material deposited in malacological collections (including types) allowed a redescription of L. alvarezii and its comparison with L. hyalina. Lyonsia alvarezii is characterized by markedly inequilateral valves, with the umbo well dislocated to the anterior region. It has considerable intraspecific variation, mainly in the ventral outline, from almost straight to sinoidal, and at the umbo, from pointed to slightly rounded. The arrangement of spinules on the outer surface of the shell is irregular, usually consisting of three to five radial rows between each pair of radial lines. Previous records of L. hyalina from southern Brazil and Uruguay were based on misidentifications of shells of L. alvarezii and of Lyonsia celeste n. sp. The latter is diagnosed by its elliptical shell, with the anterior, posterior and ventral outline rounded; its subequilateral valves; and the shell spinules restricted to the umbo region of the shell surface. Four species occur on the coast of Canada and the U.S.A: L. arenosa (Møller, 1842), L. granulifera Verrill and Bush, 1898, L. hyalina and L. floridana Conrad, 1849. Three are restricted to the southwestern Atlantic: Lyonsia alvarezii has a wide distribution, from shallow waters in northeastern (∼3°S) and southeastern Brazil (∼23°S) to Argentina (∼41°S); L. malvinensis is restricted to the Falkland Islands; and Lyonsia celeste n. sp. is known only from Uruguay and Argentina.

Zidona dufresnei Donovan, 1823 is an endemic snail of the southwestern Atlantic Ocean. In San Antonio Bay, Río Negro Province, it is commonly found in the intertidal zone all year round and from October to April the females deposit planoconvex egg capsules attached to hard substrates. The population of Z. dufresnei studied is an exception because it is unique in that inhabits shallow waters. The main goal of this study was to determine the duration of the direct intracapsular development of Z. dufresnei in the field. Results show that the intracapsular development takes 34.5 ± 3.8 days. In late developmental stages, a mean of three embryos per capsule was observed. Developmental duration under natural conditions was shorter than in lab conditions previously studied. The shorter developmental period than that reported for other temperate neogastropods may be related to the high summer water temperatures and high salinity at the location studied. Shorter embryonic duration would be important for this population of Z. dufresnei which inhabits an environment of high predation pressure on egg capsules.

An individual snail shell of Columella simplex (Gould, 1841) was discovered inside of a soybean stem from no-till field in Crittenden County, Arkansas. The shell was found on top of the frass plug of an overwintering chamber of the cerambycid beetle, Dectes texanus.

Octopus hubbsorum Berry, 1953 is an important fishery species off the Pacific coast of Mexico. It inhabits the intertidal and subtidal zones to depths of 30 m. Its occurrence has been documented in tropical and subtropical zones. In Mexico, it is in the Gulf of California and at some localities of the southern Mexican Pacific, including the Revillagigedo Islands. In this paper, the presence of a well-established population of O. hubbsorum in Bahía Magdalena (on the west coast of the Baja California peninsula) is presented. This new record expands the distribution range not only in distance but also into a temperate zone. Additionally, the maximum size records for this species are extended (1020 mm total length; 220 mm dorsal mantle length; and 3705 g total weight).

Idiosepius paradoxus (Ortmann, 1881) has been previously collected only in the four months from September to December at Usujiri, in northern Japan, which is considered its northern limit. Previous reports indicate that I. paradoxus is not able to overwinter at this distribution boundary. In winter 2006–2007, seawater temperatures were higher than in previous years. To investigate whether I. paradoxus overwinters in Usujiri, we collected specimens monthly and compared their occurrence pattern with seawater temperature data. In 2007, samples were collected between April and August, months in which they had not been previously collected in Usujiri. Winter seawater temperatures in 2007 were higher than in any other year. These results suggested that I. paradoxus successfully overwintered in Usujiri. However, winter water temperatures in 2008 returned to their usual lows, and specimens were not found in April. Therefore, overwintering success appeared to be temporary, and range expansion toward higher latitudes does not appear to have yet occurred.

The giant squid, Architeuthis Steenstrup, 1857, serves as a model for what we know and do not know about the broad biological aspects of the coleoid cephalopods. Gaps in our knowledge of taxonomy and systematics, distribution, population size, habitat use, age and growth, predation and feeding, reproduction and life cycles, and functional morphology all are examined by our review of Architeuthis natural history. Continued Architeuthis research improves our understanding of all coleoid cephalopods, and provides an avenue to engage the public in the process of science.

Bivalves share many of the “deeper” questions with the other molluscan groups - issues such as their origin and sister-group relationships within the Mollusca, and their suitability to explore molecular data in a “known” fossil framework. Other questions are more specific to bivalves, a group that radiated so successfully and nowadays predominantly specializes as infaunal and sessile epifaunal suspension feeders. This paper highlights and explores unanswered questions, from the seemingly trivial and mundane (e.g., how many species are actually out there?), to exploring enigmatic clades about which we know extremely little besides their shells, to macroevolutionary questions that could best be addressed by bivalve-based data. Fast-developing molecular approaches, including the first genome-level and transcriptomic data, a resurgence of detailed morphological and soft-anatomical research, and a renewed focus on Bivalvia by biological and paleontological workers provide us with an opportunity to address such issues. Coordination of efforts - and reciprocal illumination - across traditional disciplinary boundaries will be key factors in such endeavors.

The objective of this paper is to review the current state of our knowledge of freshwater bivalve diversity and evolution in order to identify some of the “Great Unanswered Questions” in the field. Twenty-one bivalve families have been attributed to fresh waters, but only 16 actually live and reproduce in inland waterways. Of 1209 species of freshwater bivalves, 1178 (97%) belong to eight primary freshwater families: Unionidae, Margaritiferidae, Hyriidae, Mycetopodidae, Iridinidae, and Etheriidae (all Unionoida), Sphaeriidae, and Cyrenidae (both Veneroida). The remaining 31 species represent secondary freshwater lineages of predominantly brackish/marine bivalve families. The global geographical patterns of freshwater bivalve richness are discussed, and an appendix detailing the families, genera, and species of freshwater bivalves is provided.

Although the primary freshwater bivalve families represent at least three independent radiations from marine into inland aquatic habitats, these lineages have converged on similar adaptations to life in a flowing hypoosmotic medium. For example, all have abandoned broadcast spawning and planktonic veligers. Phylogenetic studies of the Unionoida, Sphaeriidae, and Cyrenidae have also converged on a suite of common challenges: outgroup issues, biased ingroup taxon and character sampling, and atypical modes of genetic inheritance that uncouple gene trees from species trees. The recent phylogenetic literature on the three primary radiations is reviewed, emphasizing areas in need of research. Ample opportunities exist in freshwater bivalve research but progress is hindered by the limited numbers of researchers and students in the field.

Gastropods have served as research subjects for investigating questions that transcend both the taxon and the field of malacology. A major set of questions arises from repeated patterns in the microstructure, sculptural features, and coiling geometry of gastropod shells. The problem of similarity is one of distinguishing among alternative explanations of repetition and close resemblances. What explains the repetition of structural features? Are features similar as a consequence of shared ancestry (homology) or as a consequence of evolutionary convergence on good functional solutions (analogy)? There is increasing evidence for a third alternative that lies outside the evolutionary sphere, invoking the laws of physics and chemistry, building materials, and the assembly rules that apply strongly to the inorganic calcium carbonate of the gastropod shell. Three concepts are introduced to help organize the analysis of recurring similarities in the shells of marine gastropods. They are (1) remote biomineralization, (2) heterotectonic construction and ontogenetic reorganizations of shell secretion, and (3) structural funicity of the shell. Remote biomineralization produces organized structures without influence of the mantle, extrapallial space, and periostracum. Reticulate meshworks of aragonite on the exterior surfaces of larval shells are an example. Heterotectonic construction recognizes repeated instances of change in coiling geometry of the larval shell (protoconch) and the adult shell (teleoconch). Heterostrophy is an example of heterotectonic construction that is specific to the clade Heterobranchia; but there are many constructional changes that recur in other groups that are not closely-related. Examples include the set of changes that thicken larval shells (imbricate thickening) during the metamorphic reorganization of shell secretion and transition to secretion of new calcium carbonate microstructures. Funicity is a property of shell that results in recurring features that record ontogenetic history and ecological events. Funeous details include growth increments as records of periodic environmental rhythms, isotopic records of climate, and records of interaction with other organisms, including non-lethal damage inflicted by predators and modifications of shells by symbionts. Shells also record details of their post-mortem history, including a rich funeous record in deep time on and in shells in the fossil record.

Studies on the diversity of land molluscs raise a number of crucial questions that remain unanswered, or in some cases have not been asked. At the most fundamental level, we need to question the comparability of species concepts used in different studies, which influence our assessment of overall diversity and of regional differentiation. Current estimates of global diversity are likely to be too low. Beyond that, the assumption that all species can be represented by equivalent digits needs to be challenged: the range of size, habits and trophic levels needs to be taken into account. While higher taxonomic categories can be used as rough proxies for similar ecology, we have very little detailed information other than for shell size and shape, where the huge range suggests some radical differences within and among faunas. The range of niches occupied may differ among faunas: are we dealing with comparable taxonomic entities? Our knowledge of microhabitat requirements is severely deficient.

Regional species richness varies much more than maximum local (site) richness across faunas. The poor regional faunas of areas subject to glacial or periglacial Pleistocene conditions are not always impoverished at local level. While this might suggest the presence of competitive interactions, the evidence for competition is scarce. There are many cases where closely-related species live in sympatry at the smallest scales. Nevertheless, there are cases of parapatric or microallopatric distributions of congeners, and metapopulation dynamics can facilitate the co-existence of potential competitors. There may be no general rule; cases of both character displacement and convergence in sympatry are reported.

While most studies accept the traditional model of allopatric speciation to account for the development of diversity, the balance between vicariance and dispersal as driving forces remains undetermined, and clearly varies from case to case. Poor powers of active dispersal may permit genetic differentiation over very short distances, but there are a number of spectacular cases of long-distance passive dispersal that suggest that our direct estimates of dispersal are questionable. Better knowledge of actual dispersal and of the ecological requirements of land mollusc species should be priorities for the future.

In numbers, the aplacophoran mollusks are of subordinate importance amongst the Mollusca and they remain a somewhat obscure group as compared to gastropods, bivalves, or even chitons. The ongoing confusion when it comes to naming, categorizing, and classifying what is known as either the class Aplacophora with subclasses Chaetodermomorpha and Neomeniomorpha, or the two classes Solenogastres and Caudofoveata, is not helpful in this matter, either. Nevertheless the last decade has brought a number of important results when it comes to aplacophoran biology, morphology, taxonomy, and currently also aplacophoran phylogeny. These results point to a sistergroup relationship between Solenogastres and Caudofoveata, but also show that there are a number of crucial differences that support a classification into two separate classes. Here, the current status of aplacophoran research is outlined and important open questions are discussed as focus areas for future studies.

A review of the current state of knowledge on the Monoplacophora, a taxon crucial for assessing phylogeny of the Mollusca, is provided. A number of questions related to this taxon have been resolved; the seriality of some organ systems is now regarded as secondarily gained within mollusks and shared with polyplacophorans; the tergomyan-cyclomyan condition does not reflect a principal difference in organization. Other topics remain to be resolved. These concern the relationships amongst monoplacophorans and the placement of the Monoplacophora within the Mollusca. Furthermore we point out a number of issues to be investigated (e.g., mechanism of excretion or development sequence of gills and muscles, gene expression) by fine structural, ontogenetic, or molecular analyses.

Despite the diversity and importance of Mollusca, evolutionary relationships among the eight major lineages have been a longstanding unanswered question in Malacology. Early molecular studies of deep molluscan phylogeny, largely based on nuclear ribosomal gene data, as well as morphological cladistic analyses largely failed to provide robust hypotheses of relationships among major lineages. However, three recent molecular phylogenetic studies employing different markers and more data have significantly advanced understanding of molluscan phylogeny by providing well-supported topologies and generally congruent results. Here, evolutionary relationships among the major lineages of Mollusca and implications of recent findings for understanding molluscan evolution are reviewed. Most notably, all three of the recent studies reviewed herein recovered a monophyletic Aculifera, a clade including Aplacophora (Neomeniomorpha Chaetodermomorpha; worm-like molluscs) and Polyplacophora (chitons). This finding argues against the previously widely-held notion of an aplacophoran-like ancestor of Mollusca. Also, these studies counter the widely held view that Gastropoda and Cephalopoda are sister taxa - a result with important implications for the field of neurobiology where representatives of both taxa are used as models. Surprisingly, the one study that sampled the limpet-like Monoplacophora recovered it sister to Cephalopoda. Placement of Scaphopoda remains ambiguous as two studies place it sister to a Bivalvia-Gastropoda clade (Pleistomollusca) with strong support but another places Scaphopoda sister to Gastropoda with strong support. Ongoing work in several labs employing new sequencing technologies and analytical methods as well as morphological and developmental studies will undoubtedly continue to improve understanding of deep molluscan phylogeny and evolution.