Loss of planktotrophy and speciation: geographical fragmentation in the deep-water gastropod genus Bathytoma (Gastropoda,Conoidea) in the western Pacific

Dispersal capabilities are crucial in how speciation patterns are determined in marine invertebrates. Species possessing a long-living planktonic larva apparently have a dispersal advantage over those with non-planktotrophic development, and their distant populations may exchange genetic material, maintaining a broad geographical range for the species. Recent species of the gastropod genus Bathytoma (Conoidea) are all characterized by non-planktotrophic development, having most probably lost a free-swimming larva in the pre-Pliocene, as Miocene fossils have protoconchs indicating planktotrophic larval development. All have a bathyal distribution (100–1500 m), which implies that their capability for direct expansion on the bottom is restricted by both deep-sea basins and shallow-water areas, especially in insular West and South-West Indo-Pacific. Therefore, it can be hypothesized that Bathytoma populations should represent numerous, mostly allopatric taxa restricted to a single or contiguous island groups. We tested this hypothesis using molecular and morphological characters independently. One hundred and thirty-eight specimens from the Philippines, Solomons, Vanuatu, and the Coral Sea were sequenced for one mitochondrial (COI) and one nuclear (ITS2) gene, and 14 operational molecular units were recognized. When these molecular units are overlaid over shell characters, 13 species (11 unnamed) and one form of uncertain status are recognized: three occur in the Philippines, six in the Solomons and one in New Caledonia. Broad distributions (inter-archipelagic) are uncommon (three species). On the whole, the phylogeographic pattern of the diversity in the genus is rather complex and probably also reflects processes of sympatric and fine-scale allopatric speciation, and local extinctions. The eleven new species are described and named.     

Spermiogenesis in the vermetid gastropod Dendropoma petraeum (Gastropoda,Prosobranchia)

The structure and maturation of the male gonad of the Mediterranean vermetid gastropod Dendropoma petraeum are described. Histological sections of the gonads were made throughout development and gonad activity was monitored at regular monthly intervals. During the autumn months the gonad is very small and is surrounded by a large quantity of connective tissue; it becomes more voluminous from December to August, with the highest growth peak in springtime. The stages of spermatogenesis were also observed and described.     

The circatidal rhythm of the estuarine gastropod Hydrobia ulvae (Gastropoda: Hydrobiidae)

Intertidal animals display a suite of cyclic behaviours that evolved as adaptations to the predictable cycle of inundation and exposure. In estuarine habitats, mud snails from the genus Hydrobia are among the most abundant grazers, and have received considerable attention with respect to the behavioural mechanisms mediating locomotion, dispersal, and feeding, although the nature of the control of these processes has remained elusive. In particular, it is not clear whether endogenous activity patterns are related to periodic changes of microphytobenthos biomass at the sediment surface, or whether they are timed to the tidal cycle at all. In the present study, we address the crawling activity of Hydrobia ulvae under constant conditions, as well as the effects of individual size and previous short‐term exposure to tides of different range, by recording immersed individual snails under constant dark conditions. We show that the species displays an overt circatidal pattern of crawling, with activity peaks around high water, and that the start of inundation may act as an entrainment agent of the rhythm. Moreover, the results obtained indicate that smaller snails display higher levels of activity, although neither the size nor previous in situ influence of tidal range has an effect on the period and on the amplitude of the rhythm. These findings suggest that fluctuations of microphytobenthos biomass are not a sufficiently strong selective pressure to have shaped locomotor activity in H. ulvae. Moreover, feeding of H. ulvae should take place mostly during high water and be independent of periodic fluctuations of microphytobenthos biomass at the surface of the sediment. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 439–450.     

Reproductive isolation in snails of the genus Albinaria (Gastropoda: Glausiliidae)

Parapatric, morphologically characterized forms of the Mediterranean snail genus Albinaria have traditionally been regarded as biological species. Recently, this view has been challenged on the basis of small interspecific genetic distances and cross-breeding experiments. In order to test whether traditionally recognized species are reproductively isolated lineages, two cases of syntopy were analysed by means of isozyme electrophoresis. The data suggest that complete reproductive isolation is present. In one of the two cases, ecological differentiation on a small spatial scale was observed.     

Variation in shell morphology of Calliostoma zizyphinum (Gastropoda: Trochidae)

Differences in shell morphology in the intertidal prosobranchmollusc Calliostoma zizyphinum were studied from a number ofsites within four geographical regions of the British Isleswith varying exposures to wave action and crab predation. Meanvalues of damage scarring were highest in shells sampled fromStrangford Lough, Northern Ireland, and lowest in individualsfrom the Atlantic Coast. Shells collected from the Isle of Manwere smaller than those from either the Atlantic coast of Irelandor Strangford Lough. Shells from Strangford Lough had tallershells (higher aspect ratio) than shells from the County Downand Atlantic Coast and shells from the County Down coast weremore squat (lower aspect ratio) than those from all other areas.Shells from Strangford Lough were significantly thinner thanshells from all other geographical areas. The relationshipsbetween shell damage scarring and shell size and tallness werenot consistent among areas. Shells from Strangford Lough arenotable in showing a steep, positive relationship between shellsize and scarring and a steep, negative relationship betweenscarring and tallness. The unusual shell phenotypes observedin shells from Strangford Lough may be explained by rapid shellgrowth, which would not only allow Calliostoma to attain a sizerefuge from crab predators but also to recover successfullyfrom repeated crab attacks on the shell lip. Such a strategywould result in larger, thinner shells with a high number ofdamage scars. (Received 6 June 2006; accepted 20 December 2006)     

A new type of gastropod proboscis: the foregut of Hastula bacillus (Gastropoda: Terebridae)

Hastula bacillus (Deshayes) is a small terebrid gastropod which inhabits sandy surf beaches in southern Thailand, where it feeds upon spionid polychaetes. It possesses a foregut anatomy unlike that of any other gastropod. An elongate arborescent muscular organ, known as the accessory proboscis structure, is extended through the mouth during foraging. When retracted, it is folded into an 's' shape in the permanent rhynchodeum. The accessory proboscis structure bears numerous tufts of short, stiff cilia which are associated with pairs or triplets of dome-like structures. It is suggested that the structures may be chemosensory and concerned with prey location. Hastula bacillus also possesses a retractable labial tube, a long proboscis and buccal tube, dart-shaped radular teeth, an odontophore, an accessory salivary gland, a pair of salivary glands and a well-developed venom gland with muscular bulb. A comparison with other terebrid species suggests that H. bacillus is the most plesiomorphic taxon yet described from the family.     

Phylogenetic reconstruction and shell evolution of the Diplommatinidae (Gastropoda: Caenogastropoda)

The fascinating and often unlikely shell shapes in the terrestrial micromollusc family Diplommatinidae (Gastropoda: Caenogastropoda) provide a particularly attractive set of multiple morphological traits to investigate evolutionary patterns of shape variation. Here, a molecular phylogenetic reconstruction, based on five genes and 2700 bp, was undertaken for this family, integrated with ancestral state reconstruction and phylogenetic PCA of discrete and quantitative traits, respectively. We found strong support for the Diplommatininae as a monophyletic group, separating the Cochlostomatidae into a separate family. Five main clades appear within the Diplommatininae, corresponding with both coiling direction and biogeographic patterns. A Belau clade (A) with highly diverse (but always sinistral) morphology comprised Hungerfordia, Palaina, and some Diplommatina. Arinia (dextral) and Opisthostoma (sinistroid) are sister groups in clade B. Clade C and D solely contain sinistral Diplommatina that are robust and little ornamented (clade C) or slender and sculptured (clade D). Clade E is dextral but biogeographically diverse with species from all sampled regions save the Caroline Islands. Adelopoma, Diplommatina, Palaina, and Hungerfordia require revision to allow taxonomy to reflect phylogeny, whereas Opisthostoma is clearly monophyletic. Ancestral state reconstruction suggests a sinistral origin for the Diplommatinidae, with three reversals to dextrality.     

Structure and in vitro cytocompatibility of the gastropod shell of Helix pomatia

Distinguishing features of biological constructions are high stability and adaptation to their environment. Beside biocompatibility, nontoxicity and degradability these characteristics are demanded for new biomaterials in the field of tissue engineering. This study investigated the chemical composition, the organization and the in vitro osteoconductive potential of the terrestrial gastropod shell (Helix pomatia) on CAL72 and human osteoblast-like cells. Chemical composition of the biomaterial was examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM) was performed to analyze the architecture of the snail shell and the morphology of the seeded cells. A double staining procedure (FDA/PI) and a proliferation test (EZ4U) assessed the viability of the cells. Microscopical images showed the multilayered architecture of the aragonite shell with hexagonal crystals on the inner side. The cells spread well on the biomaterial and the highest proliferation rate could be measured with CAL72 cells on the inner shell surface. The osteoconductive effects of this natural biomaterial could encourage further experiments in the field of tissue engineering.     

Suspension feeding and kleptoparasitism within the genus Trichotropis (Gastropoda: Capulidae)

The marine gastropod Trichotropis cancellata is a facultativekleptoparasite, either suspension feeding or parasitically stealingfood from tube-dwelling polychaete worms. To determine whetherconclusions drawn from long-term studies in the San Juan Islands,Washington, about the relative importance of suspension feedingand kleptoparasitism can be applied generally to T. cancellataacross its biogeographic range, I expanded earlier studies toAlaska and British Columbia. Kleptoparasitism is pervasive throughoutthe range of T. cancellata, occurring with equal frequency throughoutthe areas studied. The average density and size of worm hostsare relatively constant across this range. Snail and worm densitiesare not significantly correlated at the larger scale of site(averaged over nearby sampling locations clustered around acity), but are correlated at the smaller local scale (withina sampling location). Larger worms do not support more snails.The abundance of uninfected worm hosts is usually not limiting,except potentially in some sampling locations in southwest Alaskawhere the use of a novel host (a holothurian) may be the resultof low densities of uninfected worms. Additionally, I documentedthe feeding behaviours of other trichotropid species in theseregions. Trichotropis conica is the second confirmed kleptoparasitewithin the genus Trichotropis, with kleptoparasitism as frequentin this species as in T. cancellata. Like T. cancellata, allsizes observed of T. conica are kleptoparasites. On the otherhand, Trichotropis insignis is an obligate suspension feeder.Further studies are needed to determine exactly how many timesthis behaviour has arisen and been lost in Capulidae and relatedfamilies. (Received 31 May 2007; accepted 19 October 2007)     

Geometric morphometric analysis of shell shape variation in Conus (Gastropoda: Conidae)

Geometric morphometric techniques allow for the direct quantification and analysis of variation in biological shape and have been used in studies in systematic biology. However, these techniques have not been used for species discrimination in the gastropod genus Conus, a major taxon of significant tropical reef predators recognized for their peptide‐based toxins. Here, we used landmark digitization and analysis to show that five species commonly studied for their conotoxins –Conus consors, Conus miles, Conus stercusmuscarum, Conus striatus, and Conus textile – can be effectively distinguished from each other by their shape, as manifested in the results of a principal components analysis (PCA) and the generated thin‐plate splines. Two piscivorous species, C. stercusmuscarum and C. striatus, show clear overlaps in the PCA plot, although each taxon clusters within itself, as does each of the others. The loadings on the first two principal components show that the forms of the shells' aperture and spire are particularly important for discrimination. Phylogenetic analysis using neighbour‐joining methods shows that group separations are comparable with published phylogenetic schemes based on molecular data and feeding mode (i.e. piscivory, vermivory, molluscivory). The results of this study establish the utility of geometric morphometric methods in capturing the interspecific differences in shell form in the genus Conus. This may lead to the utilization of these methods on other gastropod taxa and the creation of species‐recognition programs based on shell shape. © 2012 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 165 , 296–310.     

Predatory shell drilling by two species of Austroginella (Gastropoda: Marginellidae)

Predatory shell drilling of bivalve mollusc shells is reported for the gastropods Austroginella johnstoni and A. muscaria from south-eastern Australia. This is the first record of this feeding behaviour in the family Marginellidae. The drill holes are circular and paraboloid, with a small inner penetration hole. The corroded nature of the aragonite crystals within the drill holes suggests a chemical dissolution drilling mechanism. No obvious accessory boring organ was located. The gastropods have subepithelial gland cells in the proboscis, a pair of small salivary glands and a large foregut gland. The latter has a duct bypassing the valve of Leiblein and joining the anterior oesophagus.     

Egg capsules, eggs and embryos of the southwestern Atlantic gastropod Coronium coronatum (Gastropoda: Muricidae)

The egg capsules, eggs and embryos of the muricid gastropodCoronium coronatum are described for the first time. Capsulesare sessile, bulliform, semi-circular, with a plug in the dorsalcenter. Sutures split the capsule into two asymmetrical halves.Recently laid capsules showed the presence of 3639 (n = 2) uncleavednurse eggs with a diameter of 180–210 µm (mean= 197.4 ± 8.9). The number of early embryos was 9–11.The size of the embryos was 320 x 320 to 820–880 µm.Nine pre-hatching embryos of 3.94 mm (n = 8, SD = 0.32)were found inside the older capsule. SEM illustrations of embryosand radulae are provided. Comparison of shell and radula ofembryos with the protoconch and radulae of adults of C. coronatumrevealed that the capsule belongs to this species. (Received 18 March 2006; accepted 10 October 2006)     

The molluscan genus Cominella (Gastropoda: Buccinidae) at the Three Kings Islands

Abstract

Three endemic taxa of Cominella Gray are recorded from the Three Kings Islands, New Zealand. Cominella (Josepha) regalis n.sp. and C. (Josepha) quoyana griseicalx n.ssp. occur sympatrically in relatively shallow water (to c.50m), whereas C. (Eucominia) mirabilis mirabilis Powell is known only from c.180m. The history of colonisation by these taxa is hypothesised and discussed.     

New data on the morphology of ancient gastropods of the genus Aldanella Vostokova, 1962 (Archaeobranchia, Pelagielliformes)

The position of attachment of the shell muscle is discovered in the columellar area of the shell of the Early Cambrian univalved genus Aldanella (family Aldanellidae, order Pelagielliformes, subclass Archaeobranchia), the structure of its protoconch is described, and the presence of series of septa in the embryonic part of their shell is confirmed. These new features confidently support the position of the family Aldanellidae within the gastropod class and allow them to be considered ancestral to younger gastropod lineages with a turbospiral shell.     

A new freshwater snail genus (Hydrobiidae,Gastropoda) from Montenegro,with a discussion on gastropod diversity and endemism in Skadar Lake

Karucia sublacustrina a new species of freshwater snails (Hydrobiidae, Gastropoda) is described based on material collected from Skadar Lake (Montenegro, Albania). The new species belongs to monotypic genus Karuciagen. n. The shell morphology and body shape of the new genus resembles Radomaniola Szarowska, 2006 and Grossuana Radoman, 1973, from which it differs in the larger shells with relatively slim and a slightly, but clearly shouldered body whorl. The number of gastropods from Skadar Lake basin tallies now 50 species. The adjusted rate of gastropod endemicity for Skadar Lake basin is estimated to be 38%. By compiling faunal and taxonomic data we also aim to provide information of relevance as to conservation efforts.     

On the karyology of trematodes of the genus Microphallus and their intermediate gastropod host,Littorina saxatilis II. Karyological study of Littorina saxatilis (Gastropoda: Prosobranchia)

The karyotypes of Littorina saxatilis Olivi specimens from exposed areas of the Yarnyshnaya inlet littoral (the Kola Peninsular, USSR) consist of 34 chromosomes, i.e. 10 pairs of meta- and submetacentrics and 7 pairs of subtelo- and telocentrics. Two pairs of bi-armed homologues are much bigger than the others. On the whole these karyotypes are similar to those of the individuals from the Swedish and English populations.     

On the genus Auricullina Vassiljeva, 1998 and shell pores of the Cambrian helcionelloid mollusks

The genus Auricullina Vassiljeva, 1998 and its type species A. papulosa Vassiljeva, 1998 are redescribed based on new well-preserved material, which allows me to revise the generic diagnosis and greatly add to the morphological characterization of the type species. A new species, A. granulosa sp. nov., is described from the Botomian of Australia. The synonymy of the taxa is improved. The morphology and function of shell pores in Cambrian univalved mollusks are discussed.