Differences In Shell Morphology Research Articles

Shell shape does not accurately predict self-righting ability in hatchling freshwater turtles

Flat hydrodynamic shells likely represent an evolutionary trade-off between adaptation to an aquatic lifestyle and the instability of more rounded shells, thought beneficial for self-righting. Trade-offs often result in compromises, this is particularly true when freshwater turtles, with flatter shells, must self-right to avoid the negative effects of inverting. These turtles, theoretically, invest more biomechanical effort to achieve successful and timely self-righting when compared to turtles with rounded carapaces. This increase in effort places these hatchlings in a precarious position; prone to inversion and predation and with shells seemingly maladapted to the act of self-righting. Here, we examine hatchling self-righting performance in three morphologically distinct freshwater turtle species (Apalone spinifera, Chelydra serpentina and Trachemys scripta scripta) that inhabit similar environmental niches. We demonstrate that these hatchlings were capable of rapid self-righting and used considerably less biomechanical effort relative to adult turtles. Despite differences in shell morphology the energetic efficiency of self-righting remained remarkably low and uniform between the three species. Our results confound theoretical predictions of self-righting ability based on shell shape metrics and indicate that other morphological characteristics like neck or tail morphology and shell material properties must be considered to better understand the biomechanical nuances of Testudine self-righting.

Geometric morphometric methods for identification of oyster species based on morphology.

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.

Systematic revision of the microcystid land snails endemic to Norfolk Island (Gastropoda: Stylommatophora) based on comparative morpho-anatomy and mitochondrial phylogenetics

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

Assessment of the distribution of Ruditapes spp. in northern Mediterranean sites using morphological and genetic data

ABSTRACT In the 1970s, Ruditapes philippinarum was introduced to France at Arcachon Bay for aquaculture. At present, in Europe, R. philippinarum is often found in place of the native species Ruditapes decussatus. The aim of this study is to evaluate the distribution of these two species along the northern Mediterranean coastline using morphological and morphometric analysis. The sampling period was between June and December 2018. Among the 11 French sites, only 2 contained R. philippinarum, whereas only the indigenous species was present at the other sites. Genetic analyses were used to confirm species identity and to confirm this distribution. A site in Italy, Pialassa Baiona, was also added to the sample. This analysis of Ruditapes from multiple French sites and one Italian site highlights species-level differences in shell morphology between R. decussatus and R. philippinarum. The intraspecific morphometric analysis showed the presence of different groups depending on spatial scales (i.e. at the large scale, between the Mediterranean Sea and the Atlantic, and on the small scale, that is within the Berre lagoon in France. No relationship between morphometric and genetic variation was found. This suggests that the differences in the shell shape of Ruditapes are driven by local environmental conditions.

Kerkia Radoman, 1978 (Caenogastropoda: Hydrobiidae): endemism, apparently morphostatic evolution and cryptic speciation

ABSTRACT Kerkia is a snail genus inhabiting mainly subterranean waters. Live specimens of Kerkia were collected in the West Balkans. Mitochondrial cytochrome c oxidase subunit I and nuclear histone H3 were sequenced. Populations of Kerkia molecularly represented 10 mOTUs, each deserving a species rank. Apart from known species, five new species are described. The interspecies differences in shell morphology were slight and thus morphology did not reflect the evident molecular differences. All available information about the penes and female reproductive organs are summarised and their limited usefulness in species-level taxonomy is discussed. Kerkia seems to represent another example of morphostatic evolution, a result of non-adaptive radiation marked by the rapid proliferation of sibling species, whose ecology most probably remains the same. In Kerkia, intrapopulation genetic diversity does not (or almost does not) exist, and the same is true for intraspecies variation. At the same time, there is a high level of molecular difference between the species. Despite potential means for range expansion of the stygobiont fauna provided by interstitial habitats, which reduce the levels of endemism in some stygobiont gastropod species, the species of stygobiont Kerkia are restricted to small geographic areas. LSID: urn:lsid:zoobank.org:pub:F710D90A-4427-4C64-AAFE-5ADE89EEAABC

One, two or three? Integrative species delimitation of short-range endemic Hemicycla species (Gastropoda: Helicidae) from the Canary Islands based on morphology, barcoding, AFLP and ddRADseq data

Hemicycla mascaensis and H. diegoi are short-range endemics that occur allopatrically in small areas in the Teno Mountains in the western part of Tenerife (Canary Islands). Both taxa have been recognised as distinct species based on differences in shell morphology and genital anatomy. Preliminary molecular analyses using mitochondrial markers suggested a potential paraphyly of H. diegoi with regard to H. mascaensis. We here use multilocus AFLP data and ddRADseq data as well as distribution data, data on shell morphology and genital anatomy to assess the status of these taxa using phylogenetic analyses, species tree reconstruction and molecular species delimitation based on the multispecies coalescent as implemented in BFD* and BPP in an integrative approach. Our analyses show that, based on the analysis of multilocus data, the two taxa are reciprocally monophyletic. Species delimitation methods, however, tend to recognise all investigated populations as distinct species, albeit neither lending unambiguous support to any of the species hypotheses. The comparison of the anatomy of distal genital organs further suggests differentiation within H. mascaensis. This highlights the need for a balanced weighting of arguments from different lines of evidence to determine species status and calls for cautious interpretations of the results of molecular species delimitation analyses, especially in organisms with low active dispersal capacities and expected distinct population structuring such as land snails. Taking all available evidence into account, we favour to recognise H. mascaensis and H. diegoi as distinct species, acknowledging, though, that the recognition of both taxa as subspecies (with possibly a third yet undescribed) would also be an option as morphological differentiation is within the limits of other land snail species that are traditionally subdivided into subspecies.

Sexual dimorphism in shell morphology of mollusks of the genusViviparus– important objects of water resources of Ukraine

Bioindication assessment of water bodies of Ukraine can be carried out using the ratio of males and females of mollusks of the genusViviparus. In practice, it is very convenient to determine the sex of mollusks by the differences in their shell. Male and female freshwater snailsViviparus viviparus(Linnaeus, 1758) andV. contectus(Millet, 1813) are shown to have reliable differences in shell morphology depending on their age. There is almost no sexual dimorphism by shell morphometrics and indices in Viviparus snails aged one to three years. After three years of life, mature females have significantly larger shell width, higher body whorl, and size of the aperture. Females ofV. viviparusat the age of two to five years may be differentiated from males by the relationship of mean shell width and shell height, which is statistically significant higher than in males. This difference is explained by the different size of the mantle section genital organs of mature male and female. The obtained results should be taken into consideration in establishing the sex of viviparid snails.

Substrate-dependent shell morphology in a deep-sea vetigastropod limpet

Having a noncoiled, limpet-like shell is a characteristic shared by numerous gastropod molluscs, including many lineages outside the true limpets (Patellogastropoda) where it has evolved convergently. The shell shape of limpet-formed gastropods has often been used as a key taxonomic character, and although studies have shown that it can vary depending on the substrate morphology, these have mostly been examples from true limpets. Over a dozen origins of limpet-form are known in Vetigastropoda, and these limpets are still generally assumed to have rather stable shell forms that are useful for taxonomy and species identification. Here, we show that the vetigastropod limpet Lepetodrilus nux (Okutani, Fujikura & Sasaki, 1993) from a deep-sea hot vent in the Okinawa Trough develop distinct shell forms when living on different substrate types. Sequences of the barcoding region of the mitochondrial cytochrome c oxidase subunit I gene among the three forms only differed by 0.31–0.63% (K2P distance) in a 637 bp alignment, in line with the differences in shell morphology being intraspecific. The extent of shell form shift seen in this species is likely the largest reported for a vetigastropod limpet and provide further evidence that such plasticity is not phylogenetically constrained but is an intrinsic part of having a limpet-like shell.

Adaptive divergence in shell morphology in an ongoing gastropod radiation from Lake Malawi

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.

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

Volcanic CO2 vents are useful environments for investigating the biological responses of marine organisms to changing ocean conditions (Ocean acidification, OA). Marine shelled molluscs are highly sensitive to changes in seawater carbonate chemistry. In this study, we investigated the effects of reduced pH on the intertidal gastropod, Phorcus sauciatus, in a volcanic CO2 vent off La Palma Island (Canary Islands, North East Atlantic Ocean), a location with a natural pH gradient ranging from 7.0 to 8.2 over the tidal cycles. Density and size-frequency distribution, shell morphology, shell integrity, fracture resistance, and desiccation tolerance were evaluated between populations from control and CO2 vent sites. We found no effects of reduced pH on population parameters or desiccation tolerance across the pH gradient, but significant differences in shell morphology, shell integrity, and fracture resistance were detected. Individuals from the CO2 vent site exhibited a higher shell aspect ratio, greater percentages of shell dissolution and break, and compromised shell strength than those from the control site. Our results highlight that long-term exposure to high pCO2 can negatively affect the shell features of P. sauciatus but may not have a significant effect on population performance. Moreover, we suggest that loss of shell properties could lead to changes in predator-prey interactions.

A tale of two soft-shell clams: an integrative taxonomic analysis confirms Mya japonica as a valid species distinct from Mya arenaria (Bivalvia: Myidae)

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.

Variable plasticity in shell morphology of some Australian freshwater mussels (Unionoida, Hyriidae)

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.

Haliotis kamtschatkana Jonas, 1845 – a Single Species, not a Pair of Subspecies

Haliotis kamtschatkana kamtschatkana Jonas, 1845, and Haliotis kamtschatkana assimilis Dall, 1878, are shown to represent a single species, Haliotis kamtschatkana Jonas, 1845. This conclusion is reached by an extensive examination of shell specimens throughout the range of the species and of the animal itself. This conclusion is corroborated by no genetic differentiation existing between the subspecies at the molecular level (Gruenthal and Burton, 2005; Supernault, et al., 2010). Photoplates of specimens illustrate differences in shell morphology and colorations at various locations throughout the range of the species.

Parallel evolution of passive and active defence in land snails.

Predator-prey interactions are major processes promoting phenotypic evolution. However, it remains unclear how predation causes morphological and behavioural diversity in prey species and how it might lead to speciation. Here, we show that substantial divergence in the phenotypic traits of prey species has occurred among closely related land snails as a result of adaptation to predator attacks. This caused the divergence of defensive strategies into two alternatives: passive defence and active defence. Phenotypic traits of the subarctic Karaftohelix land snail have undergone radiation in northeast Asia, and distinctive morphotypes generally coexist in the same regions. In these land snails, we documented two alternative defence behaviours against predation by malacophagous beetles. Furthermore, the behaviours are potentially associated with differences in shell morphology. In addition, molecular phylogenetic analyses indicated that these alternative strategies against predation arose independently on the islands and on the continent suggesting that anti-predator adaptation is a major cause of phenotypic diversity in these snails. Finally, we suggest the potential speciation of Karaftohelix snails as a result of the divergence of defensive strategies into passive and active behaviours and the possibility of species radiation due to anti-predatory adaptations.

Iconography and Distribution of the Cape Verde Island Abalone, Haliotis tuberculata fernandesi Owen & Afonso, 2012, with Comparisons to H. tuberculata coccinea Reeve, 1846, of the Canary Islands

Specimens of Haliotis tuberculata fernandesi collected from Santa Luzía Island, Cape Verde Islands, are illustrated to provide additional representatives of this subspecies. Comparisons are made with Haliotis tuberculata coccinea Reeve, 1846, of the Canary Islands. Differences in shell morphology between the two subspecies are discussed in greater detail.

Divergence Preceding Island Formation Among Aegean Insular Populations of the Freshwater Snail GenusPseudorientalia(Caenogastropoda: Truncatelloidea)

Freshwater snails that inhabit islands are excellent model organisms for testing relationships between geological events and phylogeography, especially in the Aegean region. Although many Aegean islands were searched in the present study, species of the genus Pseudorientalia were only found on Lesvos, Samos, and Chios. Phylogenetic relationships between specimens living on these three islands were analysed using COI and 16S rRNA molecular markers and morphological data. A high level of diversity was found between islands. Genetic distances between clades showed differences high enough for the samples from different islands to be considered distinct species (p-distance: 0.105-0.133). These results are also supported by obvious morphological differences in shell morphology between islands. The mean divergence time between the Lesvos clade and Samos/Chios clade was 24.13 ± 3.30 Mya; between the Samos and Chios clades the divergence time was 14.80 ± 1.11 Mya. Our data suggest that high divergence may have occurred between Pseudorientalia populations during the Upper and Middle Miocene, when the Aegean region was part of a united landmass. It is possible that the observed highly divergent Pseudorientalia clades are relicts of high regional diversity that existed in the past.

DNA Barcoding Cleans House Through the Carychiidae (Eupulmonata, Ellobioidea)*

Abstract: The terrestrial, ellobioid taxon, Carychiidae provides an excellent case study for testing integrative taxonomy and addressing the plethora of historical species designations based on vague morphological characters. Since the Carychiidae are ephemeral, hermaphroditic microgastropods (< 2mm) inhabiting permanently moist aphotic zones of epigean (Carychium O. F. Muller, 1773) and subterranean habitats (eutroglobiont Zospeum Bourguignat, 1856), studies investigating their reproductive system for species delimitation have been futile. Many carychiid species designations were established during the mid-18th to 20th Century heydays of species discovery. Naturalists either split (“splitters”) species by recognizing them according to trivial differences in shell morphology or grouped them (“lumpers”) based upon common morphological traits. The concept of phenotypic variability was not considered or greatly underestimated in these species hypotheses. Although integration of DNA barcodes has since enabled...

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

The cold stenothermal nature of the Southern Ocean, and highly adapted fauna living within, raises the question of how much intra-specific variation there is among invertebrate populations, and how variation may have a role in speciation processes through ecological divergence, natural selection, and reproductive isolation. Despite decades of collecting biological material, this question remains largely unanswered, and many studies compare ‘populations’ of pooled material from wide geographic ranges to compensate for sampling constraints. In this study, variations in ecophysiological traits are explored by measuring growth, reproduction, and shell morphology among six populations of the small bivalve Lissarca cf. miliaris (Philippi, 1845) from the Southern Ocean, which experience subtle differences in temperature, disturbance, and food availability. There are significant differences in shell morphology and growth among different populations and slower growth rates at higher latitude populations. Prodissoconch sizes show an inverse ‘U’ shaped relationship with latitude, and are correlated with egg size at South Georgia and King George Island's Potter Cove. Higher brood sizes at the South Georgia population represent a trade-off with lower egg size, and correlate with shell morphology by offering lower internal capacity to brood young. Lower investment into offspring and morphological variations in L. cf. miliaris highlight the importance of local scale environmental variations on species' ecology. These variations in physical traits appear to be underestimated in the Southern Ocean, but may be important drivers of ecological divergence and speciation, which should be considered in future genetic investigations on different invertebrate populations.

Interpopulation differences in shell forms of the pearl oyster, Pinctada imbricata radiata (Bivalvia: Pterioida), in the northern Persian Gulf inferred from principal component analysis and elliptic Fourier analysis

Metapopulation characterization and discrimination of the pearl oyster Pinctada imbricata radiata in the northern part of the Persian Gulf is unknown. This study was conducted to examine differences in shell morphology of P. imbricata radiata from the Hendourabi and Lavan islands using principal component analysis (PCA) and elliptic Fourier analysis (EFA). Both EFA and PCA differentiated the shell form of the 2 populations significantly. PCA indicated that the pearl oysters from Hendourabi tended to be longer, while those from Lavan were wider and greater in thickness (width). Based on EFA, the specimens of Hendourabi Island were more fusiform than those from Lavan. In addition, the Lavan specimens were rounder than those from Hendourabi. The Lavan specimens had more diversity in form than those from Hendourabi. In conclusion, EFA and PCA approaches are clear-cut tools to identify and separate populations based on morphological characteristics, and EFA is a faster method compared with PCA in the discrimination of form in P. imbricata radiata.

Scallops Show That Muscle Metabolic Capacities Reflect Locomotor Style and Morphology

Although all scallops swim using their adductor muscle to close their valves, scallop species differ considerably in how they use their muscle during escape responses, in parallel with the striking interspecific differences in shell morphology. This provides an excellent opportunity to study links between muscle metabolic capacities and animal performance. We found that the capacity for anaerobic glycolysis and aerobic metabolism, as well as phosphoarginine levels in the phasic adductor muscle, differ with escape response strategy. Phosphoarginine contents were high in species that rely on phasic contractions (Amusium balloti, Placopecten magellanicus, and Pecten fumatus). Arginine kinase activities reflect reliance on rapid initial bursts of phasic contractions. Scallops that maintain their valves in a closed position for prolonged periods (P. fumatus, Mimachlamys asperrima, and Crassadoma gigantea) have high activities of enzymes of anaerobic glycolysis in their phasic adductor muscle. Myosin ATPase activity was lower in the nonswimming scallop, C. gigantea, than in swimming scallops. The different patterns and roles of swimming are reflected in interspecific differences in the biochemical attributes of the phasic adductor muscle. These patterns suggest coevolution of muscle metabolic capacities, patterns of adductor muscle use, and shell morphology in scallops.