Gastropod Lineages Research Articles

Antarctic and sub-Antarctic Nacella limpets reveal novel evolutionary characteristics of mitochondrial genomes in Patellogastropoda

Mitochondrial genomes (mitogenomes) provide valuable phylogenetic information and genome-level characters that are useful in resolving evolutionary relationships within major lineages of gastropods. However, for more than one decade, these relationships and the phylogenetic position of Patellogastropoda have been inferred based on the genomic architecture as well as the nucleotide and protein sequences of a single representative, the limpet Lottia digitalis. This mitogenome exhibits extensive rearrangements and several repetitive units that may not represent universal features for Patellogastropoda. Here, we sequenced the complete mitogenomes of three Nacella limpets, providing new insights into the dynamics of gene order and phylogenetic relationships of Patellogastropoda. Comparative analyses revealed novel gene rearrangements in Gastropoda, characterised by two main translocations that affect the KARNI and the MYCWQ clusters in Nacella limpets. Our phylogenetic reconstructions using combined sequence datasets of 13 mitochondrial protein-coding genes and two rRNAs, recovered Patellogastropoda, and Gastropoda in general, as non-monophyletic. These findings could be related to the long-branch attraction tendency of these groups, and/or taxon sampling bias. In our novel mitogenome-based phylogenetic hypothesis, L. digitalis is placed in a sister position to Bivalvia and Heterobranchia, whereas Nacella limpets are placed sister to a clade containing Caenogastropoda + Neritimorpha and Vetigastropoda + Neomphalina.

Morphological and ecological adaptation of limpet-shaped top shells (Gastropoda: Trochidae: Fossarininae) to wave-swept rock reef habitats.

Flattening of coiled shells has occurred in several gastropod lineages, while the evolutionary process of shell flattening is little known. The subfamily Fossarininae of the top shell family (Trochidae) is unique, because it includes four genera at various stages of shell flattening. Broderipia and Roya, have zygomorphic shells that has lost coiling, while the sister genera, Fossarina and Synaptocochlea, have respectively turbiniform and auriform shells. Therefore, comparisons of biology, habitats and detailed morphology among these four genera may help us to detect selection pressure driving shell flattening and loss of coiling. Although Broderipia has recently been identified as living symbiotically in the pits of sea urchins, the habitats and biology of the other three Fossarininae species, especially Roya are poorly known. After an extensive search on rocky shores of the Japanese Archipelago, we found live Roya eximia snails on intertidal/subtidal rock surfaces exposed to strong waves. Roya snails crept on the bare rock surface to graze periphyton at low tide, and fled into vacant barnacle shells at high tide. Comparison of the morphology of soft bodies in Fossarininae revealed that the columellar muscle of flattened species has been drastically elongated and arranged in posterior semi-outer edge of the flattened shell as observed in true limpets. The flattering and loss of coiling of the shell in Roya caused acquisition of a zygomorphic flat body, retraction of coiled visceral mass, and expansion of the foot sole. All of these changes improved tolerance against strong waves and the ability to cling to rock surfaces, and thus enabled a lifestyle utilizing both wave-swept rock surfaces and the inside of vacant barnacle shells.

Piercing Fishes: Porin Expansion and Adaptation to Hematophagy in the Vampire Snail Cumia reticulata.

Cytolytic pore-forming proteins are widespread in living organisms, being mostly involved in both sides of the host–pathogen interaction, either contributing to the innate defense or promoting infection. In venomous organisms, such as spiders, insects, scorpions, and sea anemones, pore-forming proteins are often secreted as key components of the venom. Coluporins are pore-forming proteins recently discovered in the Mediterranean hematophagous snail Cumia reticulata (Colubrariidae), highly expressed in the salivary glands that discharge their secretion at close contact with the host. To understand their putative functional role, we investigated coluporins’ molecular diversity and evolutionary patterns. Coluporins is a well-diversified family including at least 30 proteins, with an overall low sequence similarity but sharing a remarkably conserved actinoporin-like predicted structure. Tracking the evolutionary history of the molluscan porin genes revealed a scattered distribution of this family, which is present in some other lineages of predatory gastropods, including venomous conoidean snails. Comparative transcriptomic analyses highlighted the expansion of porin genes as a lineage-specific feature of colubrariids. Coluporins seem to have evolved from a single ancestral porin gene present in the latest common ancestor of all Caenogastropoda, undergoing massive expansion and diversification in this colubrariid lineage through repeated gene duplication events paired with widespread episodic positive selection. As for other parasites, these findings are congruent with a “one-sided arms race,” equipping the parasite with multiple variants in order to broaden its host spectrum. Overall, our results pinpoint a crucial adaptive role for coluporins in the evolution of the peculiar trophic ecology of vampire snails.

Molecular and morphological divergence in a stygobiont gastropod lineage (Truncatelloidea, Moitessieriidae,Paladilhiopsis) within an isolated karstic area in the Mecsek Mountains (Hungary)

Molecular and morphological divergence in a stygobiont gastropod lineage (Truncatelloidea, Moitessieriidae,<i>Paladilhiopsis</i>) within an isolated karstic area in the Mecsek Mountains (Hungary)

A phylogenetic classification of gastropod aquaporins

Successful responses to the multifarious challenges of controlling water balance are critical for snails' survival in the great diversity of habitats they occupy. Advances are being made in understanding how such challenges are approached at the molecular level, including through the study of aquaporins, which are proteins functioning to facilitate the passage of water and other small molecules across cellular membranes. Deduced aquaporin amino acid sequences from partial genomic assemblies of three neritimorph species were added to available gastropod data and sequences from other taxa to make a phylogenetic classification of these proteins using maximum likelihood and Bayesian analyses. We identified ten groups, designated as G1 to G10, containing sequences from multiple major gastropod lineages. At least six of the groups appear to be encoded by multiple genes within at least some species. Five weakly-associated sequences from Neritimorpha were not allocated to a group. The designated groups G1, G2, G3, G4, G5 and G7 (previously defined as Malacoglyceroporins) formed clades containing only gastropod sequences and were strongly supported by Bayesian inference. G1, G2, G3 and G5 were also strongly supported by maximum likelihood analyses. Group G6 (previously defined as Malacoaquaporins)was included with sequences from the oyster, Crassostrea gigas in a strongly supported clade. Groups G8 and G9 included only gastropod sequences but were not strongly supported. Groups G8 and G10 were designated to include all the gastropod sequences belonging respectively to strongly-supported clades including human aquaglyceroporins and aquaammoniaporins. Most groups have been found in a wide range of gastropod lineages but all identified representatives of group G7 belong to Apogastropoda whereas G2 is known only from Patellogastropoda and Neritimorpha.

The unique deep sea-land connection: interactive 3D visualization and molecular phylogeny of Bathyhedyle boucheti n. sp. (Bathyhedylidae n. fam.)-the first panpulmonate slug from bathyal zones.

The deep sea comprises vast unexplored areas and is expected to conceal significant undescribed invertebrate species diversity. Deep waters may act as a refuge for many relictual groups, including elusive and enigmatic higher taxa, but the evolutionary pathways by which colonization of the deep sea has occurred have scarcely been investigated. Sister group relationships between shallow water and deep sea taxa have been documented in several invertebrate groups, but are unknown between amphibious/terrestrial and deep-sea species. Here we describe in full and interactive 3D morphoanatomical detail the new sea slug species Bathyhedyle boucheti n. sp., dredged from the continental slope off Mozambique. Molecular and morphological analyses reveal that it represents a novel heterobranch gastropod lineage which we establish as the new family Bathyhedylidae. The family is robustly supported as sister to the recently discovered panpulmonate acochlidian family Aitengidae, which comprises amphibious species living along the sea shore as well as fully terrestrial species. This is the first marine-epibenthic representative among hedylopsacean Acochlidiida, the first record of an acochlidian from deep waters and the first documented panpulmonate deep-sea slug. Considering a marine mesopsammic ancestor, the external morphological features of Bathyhedyle n. gen. may be interpreted as independent adaptations to a benthic life style in the deep sea, including the large body size, broad foot and propodial tentacles. Alternatively, the common ancestor of Bathyhedylidae and Aitengidae may have been a macroscopic amphibious or even terrestrial species. We hypothesize that oophagy in the common ancestor of Aitengidae and Bathyhedylidae might explain the impressive ecological and evolutionary flexibility in habitat choice in the Acochlidiida.

The limpet form in gastropods: evolution, distribution, and implications for the comparative study of history

The limpet form – a cap-shaped or slipper-shaped univalved shell – convergently evolved in many gastropod lineages, but questions remain about when, how often, and under which circumstances it originated. Except for some predation-resistant limpets in shallow-water marine environments, limpets are not well adapted to intense competition and predation, leading to the prediction that they originated in refugial habitats where exposure to predators and competitors is low. A survey of fossil and living limpets indicates that the limpet form evolved independently in at least 54 lineages, with particularly frequent origins in early-diverging gastropod clades, as well as in Neritimorpha and Heterobranchia. There are at least 14 origins in freshwater and 10 in the deep sea, with known times ranging from the Cambrian to the Neogene. Shallow-water limpets are most diverse at mid-latitudes; predation-resistant taxa are rare in cold water and absent in freshwater. These patterns contrast with the mainly Late Cretaceous and Caenozoic warm-water origins of features such as the labral tooth, enveloped shell, varices, and burrowing-enhancing sculpture that confer defensive and competitive benefits on molluscs.

Phylogenetic relationships among superfamilies of Neritimorpha (Mollusca: Gastropoda)

Despite the extraordinary morphological and ecological diversity of Neritimorpha, few studies have focused on the phylogenetic relationships of this lineage of gastropods, which includes four extant superfamilies: Neritopsoidea, Hydrocenoidea, Helicinoidea, and Neritoidea. Here, the nucleotide sequences of the complete mitochondrial genomes of Georissa bangueyensis (Hydrocenoidea), Neritina usnea (Neritoidea), and Pleuropoma jana (Helicinoidea) and the nearly complete mt genomes of Titiscania sp. (Neritopsoidea) and Theodoxus fluviatilis (Neritoidea) were determined. Phylogenetic reconstructions using probabilistic methods were based on mitochondrial (13 protein coding genes and two ribosomal rRNA genes), nuclear (partial 28S rRNA, 18S rRNA, actin, and histone H3 genes) and combined sequence data sets. All phylogenetic analyses except one converged on a single, highly supported tree in which Neritopsoidea was recovered as the sister group of a clade including Helicinoidea as the sister group of Hydrocenoidea and Neritoidea. This topology agrees with the fossil record and supports at least three independent invasions of land by neritimorph snails. The mitochondrial genomes of Titiscania sp., G. bangueyensis, N. usnea, and T. fluviatilis share the same gene organization previously described for Nerita mt genomes whereas that of P. jana has undergone major rearrangements. We sequenced about half of the mitochondrial genome of another species of Helicinoidea, Viana regina, and confirmed that this species shares the highly derived gene order of P. jana.

Stability, variability, and parallelisms in the development of distant sensory systems: Olfactory and visual systems in the phylogeny and ontogeny of gastropods

The results of studies in the field of olfactory and visual systems of a number of gastropod representatives, differing in the general level of organization, phylogenetic position, habitat, and mode of life are given. The direction, general patterns, features, and parallels in the development of these sensory structures and related integrative brain regions in different phylogenetic lineages of gastropods are traced. Parallels in the development of the olfactory system of mollusks, insects, and vertebrates are shown. The important role of the habitat and mode of life of animals in the formation of specific patterns of evolutionary development of sensory organs is noted.

Mitogenomics of Vetigastropoda: insights into the evolution of pallial symmetry

The nucleotide sequences of the complete or nearly complete mitochondrial (mt) genomes of seven vetigastropods were determined:Angaria neglecta(Angarioidea),Phasianella solida(Phasianelloidea),Granata lyrata(Seguenzioidea),Tegula lividomaculataandBolma rugosa(Trochoidea),Diodora graeca(Fissurelloidea) andLepetodrilus schrolli(Lepetodriloidea). While the mt genomes of the superfamilies Angarioidea, Phasianelloidea, Seguenzioidea and Trochoidea conform generally to the ancestral gene order of Vetigastropoda and Gastropoda, those of the superfamilies Fissurelloidea and Lepetodriloidea have suffered important rearrangements. The gene order of the mtDNAofChrysomallon squamiferum, a representative of Neomphalina, was also analysed since it has been proposed to be closely related to Vetigastropoda, and showed a distinct arrangement. The reconstructed phylogenies recovered Neomphalina as a distinct gastropod lineage that is the sister group (only with moderate bootstrap support) of a clade including Vetigastropoda and Neritimorpha + Caeno‐gastropoda while the relative position of Heterobranchia and Patellogastropoda in the gastropod tree could not be determined definitively due to their long branches. Within the monophyletic Vetigastropoda, the superfamily Fissurelloidea was recovered as the sister group of two lineages, one including Lepetodriloidea as the sister group of Seguenzioidea + Halitoidea, the other including Phasianelloidea, Angarioidea and Trochoidea without resolved relationships. The long branches of Fissurelloidea were found to introduce significant tree instability in phylogenetic reconstruction. The new phylogeny supports that the loss of the right pallial gill occurred multiple times in vetigastropod evolution as previously suggested and that Phasianelloidea, Angarioidea and Trochoidea radiated from a common asymmetric (single‐gilled) ancestor that lived in the middle Palaeozoic.

Gross mismatch between thermal tolerances and environmental temperatures in a tropical freshwater snail: Climate warming and evolutionary implications

The relationship between acute thermal tolerance and habitat temperature in ectotherm animals informs about their thermal adaptation and is used to assess thermal safety margins and sensitivity to climate warming. We studied this relationship in an equatorial freshwater snail (Clea nigricans), belonging to a predominantly marine gastropod lineage (Neogastropoda, Buccinidae). We found that tolerance of heating and cooling exceeded average daily maximum and minimum temperatures, by roughly 20°C in each case. Because habitat temperature is generally assumed to be the main selective factor acting on the fundamental thermal niche, the discordance between thermal tolerance and environmental temperature implies trait conservation following ‘in situ’ environmental change, or following novel colonisation of a thermally less-variable habitat. Whereas heat tolerance could relate to an historical association with the thermally variable and extreme marine intertidal fringe zone, cold tolerance could associate with either an ancestral life at higher latitudes, or represent adaptation to cooler, higher-altitudinal, tropical lotic systems. The broad upper thermal safety margin (difference between heat tolerance and maximum environmental temperature) observed in this snail is grossly incompatible with the very narrow safety margins typically found in most terrestrial tropical ectotherms (insects and lizards), and hence with the emerging prediction that tropical ectotherms, are especially vulnerable to environmental warming. A more comprehensive understanding of climatic vulnerability of animal ectotherms thus requires greater consideration of taxonomic diversity, ecological transition and evolutionary history.

Phylogenomic analyses of deep gastropod relationships reject Orthogastropoda.

Gastropods are a highly diverse clade of molluscs that includes many familiar animals, such as limpets, snails, slugs and sea slugs. It is one of the most abundant groups of animals in the sea and the only molluscan lineage that has successfully colonized land. Yet the relationships among and within its constituent clades have remained in flux for over a century of morphological, anatomical and molecular study. Here, we re-evaluate gastropod phylogenetic relationships by collecting new transcriptome data for 40 species and analysing them in combination with publicly available genomes and transcriptomes. Our datasets include all five main gastropod clades: Patellogastropoda, Vetigastropoda, Neritimorpha, Caenogastropoda and Heterobranchia. We use two different methods to assign orthology, subsample each of these matrices into three increasingly dense subsets, and analyse all six of these supermatrices with two different models of molecular evolution. All 12 analyses yield the same unrooted network connecting the five major gastropod lineages. This reduces deep gastropod phylogeny to three alternative rooting hypotheses. These results reject the prevalent hypothesis of gastropod phylogeny, Orthogastropoda. Our dated tree is congruent with a possible end-Permian recovery of some gastropod clades, namely Caenogastropoda and some Heterobranchia subclades.

The mitochondrial genome of Ifremeria nautilei and the phylogenetic position of the enigmatic deep-sea Abyssochrysoidea (Mollusca: Gastropoda).

The complete nucleotide sequence of the mitochondrial (mt) genome of the deep-sea vent snail Ifremeria nautilei (Gastropoda: Abyssochrysoidea) was determined. The double stranded circular molecule is 15,664 pb in length and encodes for the typical 37 metazoan mitochondrial genes. The gene arrangement of the Ifremeria mt genome is most similar to genome organization of caenogastropods and differs only on the relative position of the trnW gene. The deduced amino acid sequences of the mt protein coding genes of Ifremeria mt genome were aligned with orthologous sequences from representatives of the main lineages of gastropods and phylogenetic relationships were inferred. The reconstructed phylogeny supports that Ifremeria belongs to Caenogastropoda and that it is closely related to hypsogastropod superfamilies. Results were compared with a reconstructed nuclear-based phylogeny. Moreover, a relaxed molecular-clock timetree calibrated with fossils dated the divergence of Abyssochrysoidea in the Late Jurassic-Early Cretaceous indicating a relatively modern colonization of deep-sea environments by these snails.

Differences in retinoid levels and metabolism among gastropod lineages: Imposex-susceptible gastropods lack the ability to store retinoids in the form of retinyl esters

The presence of a complex retinoid system was long believed to be a chordate/vertebrate novelty. However, recent findings indicate otherwise since the gastropod mollusk Osilinus lineatus was found to have the capacity to store retinoids in the form of retinyl esters (REs), a key feature to maintain a homeostatic control of retinoid levels. Here, we investigated whether such a complex retinoid system is widely distributed among gastropod lineages. Additionally, since one of the most spectacular examples of endocrine disruption in the wild, the masculinization of female gastropods (imposex) by the retinoid X receptor (RXR) agonist, tributyltin (TBT), has been linked with perturbed retinoid signaling, we also investigated if retinoid storage mechanisms in the form of retinyl esters were present in imposex-susceptible gastropods. Initially, we determined the presence of both polar (active retinoic acid isomers) and nonpolar retinoids (retinol, REs) in selected gastropod species: the limpet Patella depressa and the imposex-susceptible whelks Nucella lapillus and Nassarius reticulatus. Although all species presented active retinoid forms, N. lapillus and N. reticulatus were shown to lack nonpolar retinoids. The absence of REs, which are the common retinoid storage form found in vertebrates and in O. lineatus suggest that those species are unable to use them to maintain a homeostatic control of their retinoid levels. In order to further clarify the retinoid metabolic pathways in imposex-susceptible gastropods, a retinoid exposure study was carried out with N. lapillus. The results demonstrate that although N. lapillus is able to metabolize several retinoid precursors, it lacks the capacity to store retinoids as REs. Whether the lack of retinoid storage mechanisms in the form of REs in imposex-susceptible gastropods plays an important role in the susceptibility to RXR agonists warrants additional studies.

Nacre in Molluscs from the Ordovician of the Midwestern United States

Nacre was previously thought to be primitive in the Mollusca, but no convincing Cambrian examples are known. This aragonitic microstructure with crystal tablets that grow within an organic framework is thought to be the strongest, most fracture-resistant type of shell microstructure. Fossils described herein from the Ordovician of Iowa, Indiana, and Ohio provide supporting evidence for the hypothesis that sometime between the middle Cambrian and late Ordovician, nacre originated in cephalopod, bivalve, and possibly gastropod lineages. The correlation of independent origins of fracture-resistant nacre with increasing shell-crushing abilities of predators during the Cambrian-Ordovician suggests an early pulse in the evolutionary arms race between predators and molluscan prey.

Comparing apples with apples: clarifying the identities of two highly invasive Neotropical Ampullariidae (Caenogastropoda)

Ampullariidae comprises two lineages of freshwater gastropods: one Old World and one New World. Recent molecular work confirmed the monophyly of the family and began to clarify generic relationships, but current systematics remains unsatisfactory. With more than 300 available species group names for New World taxa alone, taxonomic confusion is rampant, as illustrated by two species that have been introduced widely and are difficult to differentiate conchologically, Pomacea maculata Perry, 1810 and Pomacea canaliculata (Lamarck, 1822). Misidentification hampers efforts to manage their spread and impacts as invasives, and prevents meaningful comparative analyses of their biology. Here we clarify the taxonomy, describe the morphological and genetic distinctiveness of the two species, and re-evaluate their biogeographic ranges. They differ most clearly genetically, with no shared haplotypes and a mean genetic distance of 0.135 at cytochrome c oxidase subunit I (COI). Differences in shell morphology are most obvious in recently hatched juveniles; the number of eggs per clutch is higher in P. maculata, and the individual eggs are smaller, so P. canaliculata hatchlings are nearly twice as large as those of P. maculata. Adult shells differ primarily in the angulation of the whorl shoulder and pigmentation of the inner pallial lip, with the latter a distinctive feature of P. maculata. They also differ in reproductive anatomy, most notably in P. canaliculata having two distinctive glandular tissues in the apical penial sheath gland, and P. maculata lacking a medial sheath gland but possessing a basal sheath gland. Pomacea canaliculata is restricted to a narrower southern range, whereas P. maculata ranges extensively throughout much of South America. Ampullaria gigas Spix, 1827 and Ampullaria insularum d'Orbigny, 1835 are herein synonymized with P. maculata. Neotypes are designated for P. maculata and A. gigas, and a lectotype is designated for A. insularum. A neotype is designated for P. canaliculata. © 2012 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 166, 723–753.

Comparing the reproductive biology of three “marsupial”, eu-viviparous gastropods (Cerithioidea, Thiaridae) from drainages of Australia's monsoonal north

In molluscs, as often found also among other groups of animals, two distinct reproductive modes are realised, viz. oviparity and viviparity. The latter frequently occurs in various lineages of freshwater gastropods, among them the “marsupial” Thiaridae with a pantropical distribution including Australia. Here the family was found to comprise at least 11 species, of which five are endemic to the continent. Of those two are highly restricted to only the central northern most region, viz. Melasma onca and Sermyla venustula. In contrast, “Thiara” australis reveals a wider range in Australia’s monsoon tropics. Brood pouch contents of these three thiarids are analysed here in order to infer details of their reproductive modes in relation to the geographic origin of individual populations, seasonality and the biometry of their shells. We found pronounced species-specific differences in the reproductive modes of all three thiarids, with M. onca having significantly more progeny in the brood pouch compared to S. venustula and“Thiara” australis. At the same time, its progeny are smaller and hatchlings are less advanced than in the latter two species. In addition, we report drainage-based intraspecific differences in the first two species. Accordingly, the head-water region of the Roper River, which drains into the Gulf of Carpentaria, apparently provides better environmental conditions that allow both M. onca and S. venustula to produce more progeny with an increased shell height as compared to popoulations from other drainages within the two species’ ranges. We suggest, in accordance with earlier studies, to differentiate more than only one mode within eu-viviparous reproductive strategies in thiarids. Studying the influence of various factors potentially correlated with interspecific as well as intraspecific differences in their reproductive biology, such as female shell size and drainage specific habitat, we show that Australian thiarids are more flexible and adaptable than previously known (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Biosynthesis and Cellular Localization of Functional Polyketides in the Gastropod Mollusc Scaphander lignarius

Opisthobranchs belong to a subclass of highly evolved and specialised marine gastropods that rely on the use of secondary metabolites for their survival. Here we report the full elucidation of the biosynthesis of aromatic metabolites, lignarenones, in one of these gastropods, the cephalaspidean Scaphander lignarius. Feeding experiments with ²H- and ¹³C-labelled precursors revealed a mixed acetate/propionate polyketide pathway primed by benzoic acid. Phenylalanine ammonia lyase (PAL), unprecedented in animals, is central to the synthesis of this aromatic precursor by oxidative deamination of L-phenylalanine to cinnamic acid. Lignarenones are synthesised in the cytoplasm of specialised eukaryotic cells named Blochmann's glands, which are distributed in biosynthetic tissue localised in the vulnerable mantle of the mollusc. This result supports the hypothesis that this lineage of gastropods has acquired the genetic information to produce the chemical substances that they use for their survival.

Body size, longevity, and growth rate in Lake Pannon melanopsid gastropods and their predecessors

We investigate potential microevolutionary mechanisms of phenotypic change in a lineage of brackish-water gastropods from Lake Pannon. The lineage exhibits a threefold increase in body size and a pronounced increase in shell shouldering over a roughly 2.5-Myr interval. We use the stable oxygen isotope profiles of 13 shells to address the question of whether large size is due to more rapid growth or to greater longevity.Results indicate that larger individuals have significantly greater longevity. Growth rates in large snails are comparable to those of their smaller-bodied ancestors.Potentially relevant selective advantages of large size include escape from predators, avoidance of resource competition, and increased fecundity. We argue that the first two advantages may have accrued to larger individuals but are not likely to have driven the trend because selection for them would favor more rapid growth rates. Fecundity selection, on the other hand, is readily envisioned in a stable, predictable environment in which the need for early reproduction is relaxed. The evolution of large body size in Lake Pannon molluscs may be comparable to evolution on many islands, where reduced pressure from competition and predation lead to characteristic changes in body size.

Genetic divergence and geographic variation in the deep-water Conus orbignyi complex (Mollusca: Conoidea).

Puillandre, N. et al. (2010) Genetic divergence and geographic variation in a deep-water cone lineage: molecular and morphological analyses of the Conus orbignyi complex (Mollusca: Conoidea).The cone snails (family Conidae) are a hyperdiverse lineage of venomous gastropods. Two standard markers, COI and ITS2, were used to define six genetically-divergent groups within a subclade of Conidae that includes Conus orbignyi; each of these was then evaluated based on their shell morphology. We conclude that three forms, previously regarded as subspecies of Conus orbignyi are distinct species, now recognized as Conus orbignyi, Conus elokismenos and Conus coriolisi. In addition, three additional species (Conus pseudorbignyi, Conus joliveti and Conus comatosa) belong to this clade. Some of the proposed species (e.g., Conus elokismenos) are possibly in turn complexes comprising multiple species. Groups such as Conidae illustrate the challenges generally faced in species delimitation in biodiverse lineages. In the case of the Conus orbignyi complex, not only are there definable, genetically divergent lineages, but also considerable geographic variation within each group. Our study suggests that an intensive analysis of multiple specimens within a single locality helps to minimize the confounding effects of geographic variation and can be a useful starting point for circumscribing different species within such a confusing complex.