Differences in Shell Morphology among Three Large Abalone Species in Japan

We examined the shell morphology of the bay mussel Mytilus trossulus (Gould) at six locations with various levels of wave exposure in Barkley Sound on the west coast of Vancouver Island, British Columbia, Canada. Young adult M. trossulus (29-35 mm shell length) collected from wave-exposed sites displayed striking differences in shell morphology from M. trossulus from sheltered sites. Mytilus trossulus from wave-exposed habitats had a lower shell height / shell width ratio and a thicker shell; they also had higher, more robust dysodont teeth, as well as a thicker hinge ligament. Examination of juveniles (12-14 mm shell length) collected from a wave-exposed shore and a sheltered shore separated by only a few hundred metres displayed similar differences in shell morphology and ligament thickness. These observations suggest that wave exposure is the cause of the observed differences in shell morphology and ligament thickness in M. trossulus. This is the first report of a correlation between wave exposure and morphology of the dysodont teeth and ligament in a bivalve. We discuss potential selective pressures that may favor characteristics of wave-exposed shells, including the probability of dislodgment and misalignment of valves in high wave energy areas.

ABSTRACTShell shape varies markedly in freshwater mussels in the order Unionoida. Freshwater mussels belonging to the genus Velesunio (Family Hyriidae) are distributed widely in the rivers and wetlands of Australia, with recent molecular evidence suggesting at least three more species within the genus Velesunio than previously described using shell morphology. This study explored differences in shell morphology between and within two major Australian drainage basins: the Murray–Darling and Lake Eyre. Differences in shell shape among the species were difficult to detect with variability in morphology, showing the greatest difference between drainage basins. For all species, there were significant differences in morphology between rivers within basins; Shells from the Lake Eyre Basin, showed small differences in shell morphology among with greater species level differences in morphology at the site scale in the Murray–Darling Basin. Extreme flow variability of Lake Eyre Basin rivers means they spend considerable time as lentic waterholes. In contrast, the rivers of the Murray–Darling Basin, while still highly variable, spend a far greater time under flowing conditions. Thus, the variability in shell morphology among sites may reflect local hydraulic variability rather than large-scale flow variability.

Associations between shell strength, shell morphology and heavy metals in the land snail Cepaea nemoralis (Gastropoda, Helicidae)

The soft-shell clam Mya arenaria Linnaeus, 1758 is a commercially important fishery resource that occurs in boreal and temperate environments in the Northern Hemisphere. Whether the soft-shell clam is a single species with a circumboreal range or a species complex also comprising Mya japonica Jay, 1857 distributed in the north Pacific has long been debated by malacologists and palaeontologists based on slight differences in shell morphology. We used an integrative taxonomic approach incorporating available Mya spp. mitochondrial COI and 16S rRNA, and nuclear 28S rRNA gene sequences, as well as spermatozoan and shell morphological characters to test the validity of M. japonica and examine the range of soft-shell clam distribution. Although differences in shell morphology were minor, the results from tree topologies, pairwise uncorrected p-distances, Automatic Barcode Gap Discovery (ABGD) and spermatozoan ultramorphological data confirm the validity of M. japonica in both its endemic region in the northwest Pacific, and as here newly reported introduced populations in British Columbia in the northeast Pacific, and show that M. arenaria is distributed in the northeast Pacific, North Atlantic, Barents Sea (Arctic Ocean) and Mediterranean. We estimate these two closely related sister species diverged 4.1-12.5 Myr during early Pliocene to late Miocene, which is consistent with current evolutionary theory regarding M. arenaria. In addition, ABGD indicated the congener Mya truncata Linnaeus, 1758 may represent a species complex, but additional evidence is still needed to clarify its taxonomic status.

Both genetic and environmental factors affect the morphology of oysters. Molecular identification is currently the primary means of species identification, but it is inconvenient and costly. In this research, we evaluated the effectiveness of geometric morphometric (GM) techniques in distinguishing between two oyster species, Crassostreagigas and C.ariakensis. We used traditional morphometric and GM methods, including principal component analysis (PCA), thin-plate spline analysis (TPS) and canonical variable analysis (CVA), to identify specific features that distinguish the two species. We found that differences in shape can be visualised using GM methods. The Procrustes analysis revealed significant differences in shell morphology between C.gigas and C.ariakensis. The shells of C.ariakensis are more prominent at the widest point and are more scattered and have a greater variety of shapes. The shells of C.gigas are more oval in shape. PCA results indicated that PC1 explained 45.22%, PC2 explained 22.09% and PC3 explained 10.98% of the variation between the two species, which suggests that the main morphological differences are concentrated in these three principal components. Combining the TPS analysis function plots showed that the shell shape of C.ariakensis is mainly elongated and spindle-shaped, whereas the shell shape of C.gigas is more oval. The CVA results showed that the classification rate for the two species reached 100% which means that C.ariakensis and C.gigas have distinct differences in shell morphology and can be completely separated, based on morphological characteristics. Through these methods, a more comprehensive understanding of the morphological characteristics of different oyster populations can be obtained, providing a reference for oyster classification and identification.

Littorina subrotundata from wave-exposed rocky shores differ consistently in shell and radula morphology from those found in wave-protected salt-marshes. To determine if the two morphological forms of this gastropod represent separate species, clades, or ecotypes, DNA sequencing and single-stranded conformational polymorphism (SSCP) analysis were used to assay variation in a 480 bp fragment of the mitochondrial cytochrome-b gene. Several nested analyses of molecular variance (AMOVA) were then performed to test if grouping populations by geographical region or habitat type better explained the distribution of cytochrome-b haplotypes among some northeastern Pacific populations. The analysis by geographic region resulted in a significant variance component that explained 53% of the variance, whereas the analysis by habitat type was not significant. These results, along with previous studies showing that the differences in shell morphology among different forms have a heritable component, suggest that the two forms are ecotypes and not separate species or clades as had been previously proposed. These results also imply that each ecotype has evolved independently in each geographic area and that the morphological similarity of individuals from the same habitat type is most likely the result of parallel evolution.

Rochia nilotica (Linnaeus, 1767) previously known as Trochus niloticus Linnaeus, 1767, is known in Indonesia by the local name “lola” or “lolak”. In Indonesian waters, “lola” is easily and widely found, its shiny shell has a high selling value and is an industrial commodity with an export orientation. The other most similar species is Trochus maximus F. C. L. Koch, 1844. In adult shells, T. niloticus and T. maximus are easily distinguished by the shape of their shells; but their juvenile and semi-adult shells are easily confused with one another. Both species have large shells, 110-120 mm in diameter and 115-140 mm in height. Initially, these two species were included in the genus Trochus Linnaeus, 1758 of the family Trochidae Rafinesque, 1815. Bouchet & Rocroi, 2005 in the “Taxonomy of the Gastropoda“ approved the validity of the family Tegulidae Kuroda, Habe, & Oyama, 1971 of the superfamily Trochoidea Rafinesque, 1815, separate from the family Trochidae Rafinesque, 1815. These two large species are included in the genus Rochia Gray, 1857 from the family Tegulidae, becoming Rochia nilotica (Linnaeus, 1767) and Rochia maxima (F. C. L. Koch, 1844). Included in the family Tegulidae, among which are the genera Rochia Gray, 1857; Tectus Montfort, 1810; and Tegula Lesson, 1833. This paper discusses the differences between the two species Rochia nilotica (Linnaeus, 1767) and Rochia maxima (F. C. L. Koch, 1844) in terms of shell morphology. KEYWORDS: Tegulidae, Rochia, nilotica, maxima

BackgroundEcological speciation is a prominent mechanism of diversification but in many evolutionary radiations, particularly in invertebrates, it remains unclear whether supposedly critical ecological traits drove or facilitated diversification. As a result, we lack accurate knowledge on the drivers of diversification for most evolutionary radiations along the tree of life. Freshwater mollusks present an enigmatic example: Putatively adaptive radiations are being described in various families, typically from long-lived lakes, whereas other taxa represent celebrated model systems in the study of ecophenotypic plasticity. Here we examine determinants of shell-shape variation in three nominal species of an ongoing ampullariid radiation in the Malawi Basin (Lanistes nyassanus, L. solidus and Lanistes sp. (ovum-like)) with a common garden experiment and semi-landmark morphometrics.ResultsWe found significant differences in survival and fecundity among these species in contrasting habitats. Morphological differences observed in the wild persisted in our experiments for L. nyassanus versus L. solidus and L. sp. (ovum-like), but differences between L. solidus and L. sp. (ovum-like) disappeared and re-emerged in the F1 and F2 generations, respectively. These results indicate that plasticity occurred, but that it is not solely responsible for the observed differences. Our experiments provide the first unambiguous evidence for genetic divergence in shell morphology in an ongoing freshwater gastropod radiation in association with marked fitness differences among species under controlled habitat conditions.ConclusionsOur results indicate that differences in shell morphology among Lanistes species occupying different habitats have an adaptive value. These results also facilitate an accurate reinterpretation of morphological variation in fossil Lanistes radiations, and thus macroevolutionary dynamics. Finally, our work testifies that the shells of freshwater gastropods may retain signatures of adaptation at low taxonomic levels, beyond representing an evolutionary novelty responsible for much of the diversity and disparity in mollusks altogether.

Differential adaptations between cold-stenothermal environments in the bivalve Lissarca cf. miliaris (Philobryidae) from the Scotia Sea islands and Antarctic Peninsula

Effects of long-term exposure to reduced pH conditions on the shell and survival of an intertidal gastropod

Summary1.Margaritifera hembeliis a threatened mussel limited to twenty‐two headwater streams in the Red River drainage in central Louisiana, USA. This study evaluated intraspecific variation in density, growth, size and age structure and shell morphology among several isolated populations. This study also identified the host fish and considered the role that host fish distribution played in determining mussel recruitment.2. Mussels were aggregated in beds and average densities differed among streams. However, maximum mussel densities in beds were similar in all streams; the observed maxima were among the largest for monospecific mussel beds in North America, often exceeding 300 individuals m–2.3. The maximum size reached by individuals differed among streams, but all size distributions were skewed towards larger individuals. A repeated measures analysis of tagged mussels in four populations, over a 2‐year period, indicated 2‐fold differences in growth rates among streams, and significant variation among years. Growth rates were not affected by local population density. Maximum ages reached, determined indirectly by comparing growth rates, varied from 45 to 75 years. A canonical discriminant analysis also revealed significant differences in shell morphology across populations.4. Half of the populations showed evidence of recent recruitment, and these sites had fish assemblages dominated by the host fishNoturus phaeus(Taylor). Host fish abundance appeared more important than adult mussel density in explaining recruitment patterns.5. Considerable intraspecific life history variation suggests that management strategies for this species should be stream‐specific, with emphasis on ensuring long‐term habitat stability.

Air pollution control lit

We compared shell morphology and DNA sequences of the ectosymbiotic bivalves Koreamya (Montacutidae) attached to two different species of inarticulate brachiopods Lingula collected from South Korea. There are some differences in shell morphology between K. arcuata (A. Adams, 1856) attached to Lingula anatina and K. sp. attached to L. adamsi, such as shell outline, periostracum and hinge teeth. However, there are very few differences in DNA sequences of COI and ITS1 suggesting that the two forms of Koreamya are genetically conspecific. While many ectosymbiotic Galeommatoidea species have been reported to live commensally with only one host species, this study suggested that K. arcuata lives commensally with at least two species of Lingula and that its shell morphology may vary according to the host species.

Predation on a tropical spinose gastropod: the role of shell morphology

Norfolk Island harbours a rich land snail diversity dominated by the Microcystidae and Helicarionidae that are currently represented by 10 endemic genera and 27 accepted species and subspecies. We comprehensively revise the taxonomy of these taxa using comparative morphology and phylogenetic analyses of the mitochondrial genes COI and 16S. We demonstrate that most ‘helicarionid’ species belong to Microcystidae with only a single species of Helicarionidae present (Dendrolamellaria mathewsi). The Norfolk Island microcystids comprise five major clades. These clades may have independently colonised the Norfolk Island group; however, clarity may only be achieved in a broader phylogenetic context that incorporates the study of extralimital groups. Three clades have radiated in situ into multiple endemic species. Based on our findings, we recognise the previously accepted genera Iredaleoconcha, Nancibella and Roybellia as junior synonyms of Allenoconcha, and Mathewsoconcha and Quintalia as junior synonyms of Advena, based on the close phylogenetic relationships. Furthermore, we confirm the previous treatment of Lutilodix, Parcolena and Dolapex as junior synonyms of Fanulena and Belloconcha as a synonym of Advena, bringing the total number of Norfolk Island microcystid genera to five. Secondly, we provide revised descriptions for each of these genera. Thirdly, we remove Allenoconcha belli, A. mathewsi, A. monspittensis, A. perdepressa and A. royana from the synonymy with Allenoconcha basispiralis. We also remove Helix patescens from synonymy with Quintalia flosculus, treating this as a member of Allenoconcha, and resurrect Advena campbellii nepeanensis and Quintalia stoddartii intermedia as accepted subspecies. Based on comparative morpho-anatomy, we treat Allenoconcha mathewsi and A. monspittensis as junior synonyms of Allenoconcha royana, A. inopina as a junior synonym of Allenoconcha caloraphe, Fanulena fraternus as a junior synonym of F. amiculus, Advena campbellii charon as a synonym of Advena campbellii campbellii, Mathewsoconcha belli, M. compacta and M. norfolkensis as junior synonyms of Advena suteri, M. elevata as a junior synonym of Advena grayi, and M. microstriatum as a junior synonym of Advena phillipii. Lastly, we describe three new species, Allenoconcha evansorum sp. nov., A. margaretae sp. nov. and A. varmani sp. nov. In summary, we accept 27 microcystid species and subspecies all of which are endemic to the Norfolk Island group. We provide recent and historical distribution data for each species and demonstrate that seven species or subspecies are probably extinct. All species are well differentiated in terms of basal branch lengths in the phylogenetic tree, but this distinction is not consistently reflected in the external morphology. Some closely related sister-taxa are very similar in shell morphology whereas others exhibit highly distinctive shells. We hypothesise that these stark differences in shell morphology may result from adaptation to different ecological niches, yet we currently lack a detailed understanding of the underlying evolutionary mechanisms. ZooBank: urn:lsid:zoobank.org:pub:BEFC0F76-4405-4EE7-9060-B7D9FB84BCB1