Abstract Harmful algae can cause economic damage to fisheries and tourism. Additionally, toxins produced by harmful algae and ingested via contaminated shellfish can be potentially fatal to humans. Monitoring these harmful algae can be difficult as determining cell morphology by light microscopy may be insufficient to give definitive species attribution. The goal of the EU FP7 project MIDTAL (microarrays for the detection of toxic algae) was to achieve rapid species identification using species-specific probes for rRNA genes in a microarray chip format. Field samples from the Orkney Islands, an area of the UK that has a number of nuisance and toxic species, were tested with the second generation of the microarray chip. Species-specific probes were looked at for the toxin-producing dinoflagellates Alexandrium tamarense Group III (North American clade) and Dinophysis acuta and also general class probes for Dinophyta, Heterokontaphyta and Prymnesiophyta over the course of a year. These were compared with light microscopy cell counts. A good agreement in determining presence and absence between the methods was found. The second generation microarray is potentially more sensitive than cell counts. However, further work is needed to ensure that the microarray signal for each species provides an accurate quantitative assessment.

Abstract Bivalves have been important members of marine communities since the early Palaeozoic, in terms of both their numerical abundance and diversity. They are particularly prevalent in shallow shelf sediments, but they have also conquered the intertidal zone as well as the deep sea, where they are successful predators and key components of some vent communities. They have also invaded freshwater systems a number of times, where today they are important (and costly) foulers. In terms of general community structure, bivalves are important as prey items for a range of different predatory groups, and as major space occupiers, particularly on hard substrata where space may be limited. The abundance and diversity of both Recent and fossil bivalves have made them attractive subjects for both zoologists and palaeontologists, and both disciplines have contributed to the present system of classification and the understanding of their phylogenetic relationships. However, somewhat inevitably, the focus of the two groups has been rather different, with zoologists concentrating on anatomical characters such as those associated with the gills and stomach, whilst palaeontologists have necessarily dwelt on hard-part characters such as dentition and shell microstructure. It is becoming increasingly clear, however, that convergence and parallelism is rife within the class and more integrated approaches are necessary to unravel these. The last major attempt to integrate the palaeontological and zoological approaches to bivalve evolution was more than 20 years ago, at the Royal Society of London meeting in 1977. The resulting volume of the Philosophical Transactions of the Royal Society of London

Abstract The classification of the Pteriomorphia, a major division of the Bivalvia with Ordovician origins, is controversial both among palaeontologists and neontologists. To elucidate phylogenetic relationships new near-complete 18S rDNA sequences of 26 Pteriomorphia, three Protobranchia, three Heterodonta, one Anomalodesmata and three Scaphopoda were obtained, aligned with 71 other published molluscan sequences, and analysed with parsimony, maximum likelihood and spectral analysis. Although Bivalvia appear diphyletic due to heterogeneity of substitution rates among lineages, monophyly of Protobranchia, Heteroconchia and Pteriomorphia is supported. The heteroconch Lucinida, Myoida and Venerida are not monophyletic, and Anomalodesmata arise from within Heteroconchia. The basal nodes of Pteriomorphia have little support but two major clades, [Pinnoidea (Ostreoidea + Pterioidea)] and [(Anomioidea + Plicatuloidea) + (Limoidea + Pectinoidea)], are resolved with more confidence. The strongly supported clade of Anomioidea + Plicatuloidea, the separation of Pinnoidea from Pterioidea and most of the intrafamiliar relationships are not in accordance with morphological classifications. Combining these results with selected morphological characters, a phylogenetic hypothesis is proposed showing Mytiloidea and Arcoidea as the basal pteriomorph groups, the latter giving rise to the clade uniting the pinnoid-ostreoid-pterioid and the anomioid-limoid-pectinoid lines.

Abstract Despite widespread agreement on the monophyly of several major taxa of bivalves, others remain uncertain and the relationships among them are debated. The present study compares new and published morphological phylogenies with new analyses based on 18S gene sequences. All but one family and all superfamilies in the Bivalvia were monophyletic in all the analyses. Several higher taxa, including most subclasses and orders, were also resolved as monophyletic. Only Myoida shows strong evidence for polyphyly, with at least two origins from Veneroida. Autobranchia was supported as monophyletic in the parsimony analyses. Within Pteriomorphia, Ostreoida is the sister taxon of Pterioida, if not derived from within it, rather than closest to Pectinoida. The numerous points of agreement with morphology based analyses suggests that both types of evidence are converging on a common phylogeny; however, differences remain to be resolved by further study.

Abstract Parsimony analysis suggests derivation of the Bivalvia from monoplacophorans rather than from rostroconchs, and additionally indicates that a phylogenetic classification of the Bivalvia can be achieved by erecting the superorder Nuculaniformii nov. and the order Nuculanoida nov. for the superfamily Nuculanoidea; relegating all other palaeotaxodonts to the superorder Nuculiformii; restricting the order Nuculoida to the families Nuculidae and Pristiglomidae; expanding the order Solemyoida to include ctenodontid genera as basal plesions; restricting the superorder Heteroconchia to palaeoheterodonts and heterodonts, exclusive of the Modiomorphidae; relegating the new family Evyanidae, the Colpomyidae, Matheriidae and Modiolodontidae to near-basal plesion status within the superorder Pteriomorphia; restricting the Mytiloida to the superfamily Mytiloidea, inclusive of modiolopsid genera as basal plesions; placing Ortonella as a basal plesion within the Cyrtodontoida; expanding the order Pectinoida to include the Myodakryotidae and the suborders Limina and Pectinina; and expanding the superfamily Arcoidea to include the frejid genera and Catamarcaia as basal plesions, and the family Glyptarcidae. Modiomorphid anomalodesmatans appear to be more closely related to the Pteriomorphia than to the Heteroconchia, and Evyana lies close to the common ancestry of modiomorphids and colpomyid pteriomorphians. Arcoids may have evolved from left–right symmetrical but otherwise rhombopteriid-like ancestors, rather than from actinodontoids or directly from cyrtodontids. The new family Eodonidae is proposed to distinguish the nacreous genus Eodon from the non-nacreous Astartidae within the superfamily Crassatelloidea.

Abstract In the 30 years since publication of the bivalve Treatise , (Moore, R. C. (ed.) 1969. Treatise on Invertebrate Paleontology. Part N. Mollusca 6, Bivalvia , Geological Society of America and University of Kansas) important new faunas have been described from the early and mid Cambrian and from the early and mid Ordovician. These contain significant new forms, including some long-ranging intermediate groups, that indicate the relationships between the principal bivalve clades, but lack of fossils from the late Cambrian and earliest Ordovician is a major hindrance. The principal phase of bivalve diversification followed on from the evolution of the filibranch gill in the latest Cambrian or earliest Ordovician. The fundamental division of the class is into two subclasses, Protobranchia and Autolamelli branchiata; links between the two can be demonstrated in the early Ordovician. Major divisions of each subclass are recognized as superorders. Within the Protobranchia, the Nuculoida developed specialist food-gathering palps and an enlarged foot. Diverging early from the protobranch stock were other bivalves that lived symbiotically with sulphur-oxidizing chemoautotrophic bacteria; this allowed colonization of anaerobic substrates and produced two distinct stocks: the deeply infaunal anteriorly elongate Solemyoida and the shallower infaunal Nucinelloida. The Autolamellibranchiata, initially identified by strongly asymmetrical hinges, diversified in three directions, each characterized by distinctive hinges. The Trigonioida were characterized by ligamental nymphs and frequently denticulate teeth, and rapidly regained greater symmetry; the Anomalodesmata also developed a strong ligamental insertion within nymphs and largely lost their dentition, whilst the Heteroconchia, principally with a shell including a complex crossed-lamellar structure, had various combinations of cardinal and lateral teeth. Heteroconch diversifications were mainly in the Mesozoic and Cenozoic, but one Ordovician group, the Glyptarcoidea, is a good ancestor for the Pteriomorphia. The following new taxa are proposed: Cardiolarioidea superfam. nov., Eritropidae fam. nov. and Catamarcaidae fam. nov.

Abstract The taxonomic history of the late Jurassic–Cretaceous rudist bivalves (Superfamily Hippuritoidea) is reviewed and a new phylogeny based on cladistic analysis of 32 skeletal characters is proposed. Informative characters include: relative thickness and structures of the outer (calcitic) shell layer; valve asymmetry and attachment to the substrate by either the left or right valve; form of the ligament; and, in the aragonitic inner shell, the dentition and shelly supports (myophores) for the adductor muscles, as well as accessory cavities and blind-ending (pallial) canals. The myocardinal complex (teeth and myophores) is especially important for discriminating clades previously lumped in paraphyletic or even polyphyletic taxa (e.g. Caprinidae, sensu lato, in the bivalve Treatise (Moore, R. C. (ed.) 1969. Treatise on Invertebrate Paleontology, Part N. Mollusca 6, Bivalvia, Geological Society of America and University of Kansas). As outgroup, a megalodontid bivalve was used, as this shares three derived traits (massive dentition, modified parivincular ligament and posterior myophores) in common with rudists. The clade of all rudists is united by possession of an outer shell layer of fibrillar prismatic calcite (albeit greatly reduced in a few taxa). Two subclades are distinguished according to the attachment of the shell – either by the left valve (all ‘diceratids’, except Diceras and Valletia, plus the monophyletic requieniids), or by the right valve ( Diceras, Valletia and all other rudists). Monophyly of some previously established families is substantiated. These include Caprinidae, sensu stricto (Skelton, P. W. 1978. Philosophical Transactions of the Royal Society of London, Series B, 284, 305–318), Radiolitidae (with Agriopleura as sister taxon) and Hippuritidae (with Tepeyacia emerging as a possible sister taxon), while others are resolved into distinct clades. There is some evidence for the Polyconitidae Mac Gillavry ( 1937 ), though with negligible bootstrap support.

Abstract Although ancient anomalodesmatans were apparently abundant shallow and deep burrowers, in Recent seas the subclass comprises some of the most specialized and rarest of all bivalves. The morphological adaptations associated with diverse life habits has persistently frustrated attempts to achieve a widely accepted scheme for the relationships between extant families. A cladistic analysis, using 43 informative anatomical and shell characters for each of the extant anomalodesmatan families has produced a single, reasonably robust tree which is in broad, albeit imperfect, agreement with the known fossil record of the subclass. This total evidence tree places the Pandoridae, Lyonsiidae, Cleidothaeridae and Myochamidae, and also the Thraciidae, Periplomatidae and Laternulidae in monophyletic groups. Carnivory appears diphyletic, with the Parilimyidae separated from the ‘septibranch’ families (Cuspidariidae, Verticordiidae, Lyonsiellidae and Poromyidae) which form a monophyletic group. The enigmatic tube-dwelling Clavagellidae appear as a sister group to the ‘septibranchs’. Re-analysis of the data matrix using only those 18 characters which could be scored from shell characters alone, produced a tree which contradicted the total evidence tree rather than producing a poorly resolved version. The degree of convergence shown by shell characters make it, at least at present, difficult to include the extinct anomalodesmatan families in a cladistic analysis.

Abstract Unionid bivalves or freshwater pearly-mussels (Unionoidea: Unionidae) serve as an exemplary system for examining many of the problems facing systematists and conservation biologists today. Most of the species and genera were described in the late 1800s and early 1900s, but few phylogenetic studies have been conducted to test conventional views of species and classification. Pearly-mussels of Gulf Coastal drainages of the southeastern United States from the Escambia (southern Alabama to Florida) to the Suwannee Rivers (Florida) are a unique fauna comprised of approximately 100 species, with about 30 endemic to the region. In this study, mitochondrial cytochrome c oxidase subunit I and 16S rRNA gene sequences were used to test the monophyly and to estimate evolutionary relationships of five unionid species representing three different genera. The molecular phylogenies depict all three genera as polyphyletic. The prodigious polyphyly exhibited within unionids is due to incorrect notions of homology and false assumptions about missing anatomical data. In contrast, the molecular phylogeny provides evidence to support the recognition of all five unionid species as distinct evolutionary entities. Furthermore, molecular genealogical evidence supports the elevation of Quincuncina infucata (Conrad) of the Suwannee River to species level, for which Q. kleiniana (Lea) is available.

Abstract A robust phylogeny for the Unionoida is emerging and presumed relationships of some major clades are being questioned. The Etheriidae or freshwater oysters has been a distinct family for over 160 years and currently contains three cemented genera: Acostaea (Columbia, South America), Pseudomulleria (India) and Etheria (Africa and Madagascar). Starobogatov ( 1970 , Nauka , 1–372), Mansur and da Silva ( 1990 , Amazoniana , 11 (2), 147–166) and Bonetto ( 1997 , Biociências , 5 , 113–142) present conflicting testable hypotheses regarding the evolution of these taxa. Using cytochrome c oxidase subunit I DNA sequences the evolutionary relationships of these three genera has been examined, by comparing them to representatives of 30 other unionoid taxa from around the world. These analyses place Acostaea and Etheria within the Mycetopodidae while Pseudomulleria falls within the Unionidae. A monophyletic Etheriidae, composed of cemented freshwater bivalves, is not supported by the present analyses. Furthermore, the analyses indicate that cementation in the Unionida has evolved at least twice.

Abstract Pteriomorphian spermatozoa, like those of most other bivalves, are of the classic aquasperm type (conical acrosomal vesicle, short to rod-shaped nucleus, short midpiece composed of two centrioles and a ring of spherical mitochondria, a simple flagellum). Whereas most other bivalve subclasses show at least some defining acrosomal feature(s), this does not appear to be the case within the Pteriomorphia. While this could indicate non-monophyletic status, it also correlates with the fact that the Pteriomorphia are a very old and very successful group of bivalves. Acrosomal similarities suggest a close link between the Ostreoidea and Limoidea (acrosomal vesicle with wedge-shaped apical zone; radiating plates present but not well developed); and between the Pterioidea, Pinnoidea and Pectinoidea (dense anterior layer; very well developed radiating plates). For supposedly closely related taxa, the Arcoidea and Limopsoidea (both Arcoida) differ markedly from each other in acrosomal shape and substructure. The affinities of the Anomioidea and even more so the Mytiloida remain uncertain, the latter possibly connected with the Pterioida or, more likely, removed from the rest of the Pteriomorphia (mytiloid acrosomes show concentric lamellae). A very close relationship between the Pectinidae and Spondylidae of the Pectinoidea is demonstrated (dense anterior layer of acrosome recurved). Within the Mytilidae (Mytiloidea) there is substantial variation in sperm morphology between supraspecific taxa especially at the subfamial level.

Abstract Examination of sperm ultrastructure in six out of eight of the living species of giant clams (‘Tridacnidae’) supports reduction in status of the Tridacnidae to a subfamily of the Cardiidae (Tridacninae), as suggested by recent cladistic analyses based on shell, anatomical and molecular characters. Tridacninae spermatozoa are all of the aquasperm type, featuring, in anterior–posterior sequence: a conical acrosomal vesicle, an oblong to rod-shaped nucleus, a short midpiece region (proximal and distal centrioles surrounded by four round mitochondria); and a flagellum (9 + 2 pattern axoneme). Substantial differences occur between species with respect to the shape and length of the nucleus, and in the spatial relationship between the acrosomal complex and the nuclear apex. Although the two extant genera can be distinguished on sperm features – Tridacna , nuclear peg associated with acrosome, centriolar connective absent; Hippopus , nuclear peg absent, connective present – no defining feature of the Tridacninae can be detected. Within Tridacna , the species T. (Chametrachea) maxima and T. (C.) crocea are distinguished from other species of the genus by a much finer nuclear peg and a considerably smaller acrosome. In contrast, and against expectation, T. (C.) squamosa shows acrosomal and nuclear dimensions very close to those obtained for T. (Tridacna) gigas. Recently proposed phylogenies and classificatory changes for ‘tridacnids’ are discussed in the light of available sperm data.

Abstract All Lucinidae species studied so far possess sulphide-oxidizing, chemosymbiotic bacteria housed in bacteriocytes of gill filaments. The ecology, functional anatomy and evolution of the Lucinidae must be considered in relation to this symbiosis. The ctenidia have been extensively studied but other anatomical structures peculiar to lucinids have received much less attention. Reviewed are the morphological diversity of living lucinids, highlighting features of their anatomy including ctenidia, pallial apertures, anterior adductor muscle, pallial blood vessel and mantle gills. The latter are much more complex than previously understood and are here redescribed. They comprise folded structures located near the anterior adductor muscle in Codakia, Phacoides and Lucina , and on the septum of Anodontia. These are interpreted as secondary respiratory surfaces, their location enabling the separation of the anterior inflow of oxygenated water from sulphide-containing water. The latter is released from the sediment by the probing activities of the highly extensible foot and is pumped over the gill through the pedal gape and perhaps also via the exhalant tube. The shell features of Ilionia from the Silurian Period suggests that the lucinid chemosymbiosis is an ancient association.

Abstract Anomalous mound-forming limestones, here termed the Kuhnpasset Beds, occur within Late Barremian (Early Cretaceous) mudstones on Wollaston Forland, Northeast Greenland. The normal mudstones contain a sparse fauna of small nuculoids, arcoids and inoceramids; by contrast, the mounds contain an unusual faunal assembage, dominated by large bivalves. These include an abundant lucinid, Cryptolucina kuhnpassetensis sp. nov., and, less commonly, Solemya , both known seep-associated genera. Locally, a large modiomorphid, Caspiconcha whithami gen. et sp. nov., is common and reaches > 300 mm in length and has a shell up to 28 mm thick. Also, the wood-boring bivalve Turnus is abundant in driftwood. Gastropods are rare, but the associated cephalopod fauna includes ammonites, belemnites, nautiloids and a remarkable large orthoconic phragmocone. The form of the mounds with calcite-cemented tube systems, associated laminated calcite crusts and void fills, together with the fauna, is analogous to those of methane-based cold-seep complexes. However, preliminary studies indicate that much of the original aragonitic shell is now replaced by silica. This precluded conclusive geochemical studies based on the shells themselves. It is believed that the mounds formed on the seafloor in a mid- to outer shelf situation at the end of a period of extensional rifting on the eastern Greenland passive Atlantic margin. The vents occur near the footwall crest of a tilted fault block. The underlying faults may have provided routes or influenced direction of movement for nutrient migration. Source rocks were probably the Late Jurassic black shales from depths of < 600–1200 m. If methane was being generated, it was probably forming by shallow-depth organic breakdown rather than by thermogenic processes, which require greater burial.

Abstract The structure of the pallial, ectopic eye of Patinopecten yessoensis is described and shown to be of the typical pectinid form, located on the middle mantle fold. The cornea is, however, a tall epithelium and, with the lens, forms a Cartesian oval, unlike the lens alone in other pectinids which functions to counter spherical aberration. The basal cell layer beneath the retina and argentea is poorly pigmented, although this may be countered by the fact that the optic tentacle epithelium itself is apically heavily pigmented. It is generally assumed that pectinid pallial eyes, being able to perceive a moving image, are used to warn of vicinal predators, resulting in swimming. However, this does not seem to be the case; although crabs and starfish, in particular, are known predators of scallops, which respond by swimming to the latter, they do so (usually) on receipt of mechanical and chemical stimuli, not visual. Some scallop species live in seagrass beds and there is evidence that these may afford protection. Scallops are visually attracted to the waving fronds. Scallops may also make relocation movements and, in more specialized taxa, e.g. species of Amusium , can swim for several metres. The visual sense of scallops is poorly understood and although pallial eyes may have developed early in the ancestry of the Pectinidae, as an antipredation sense organ, they may, in the descendants, now have a different, but perhaps related, function, although what this is, is unknown. Pectinid pallial eyes may improve the efficiency of photon capture in low light intensity subtidal habitats but for what purpose is unclear, since even if they are functioning as optical ‘burglar alarms’, what could they see in such a situation, especially as there is no brain to formulate an image?

Abstract Studies on the digestive system of the Teredinidae are useful for a better understanding of the evolution of these bivalves in relation to the xylophagous habit. Neoteredo reynei and Psiloteredo healdi , two common species in Brazilian mangroves, have evolved differently in their methods to use wood as food, despite the similarities in the anatomy and functioning of their globular type II stomachs. N. reynei is predominantly xylophagous throughout its life, while P. healdi , despite its predominant suspension-feeding habit, uses wood more efficiently as the animal grows older. The outstanding differences that allow these conclusions are the large size of the appendix and anal canal in N. reynei , always conspicuous and packed with wood, and the small appendix of P. healdi , which increases in size with age. Based on anatomical data and revision of the literature, it is suggested that in both species the appendix, and also the anal canal in N. reynei , is of primary importance in the digestion of wood and absorption of nutrients, counterbalancing the reduced specialized digestive diverticula.

Abstract Recent data on the distributions of cilia and mucocytes on the bivalve gill abfrontal surface are analysed with respect to evolutionary relationships of the principal autobranch gill types. From the primitive function as a mucociliary cleaning surface in the protobranchs, two evolutionary trajectories are evident: (1) progressive reduction of both cilia and mucocytes with resultant loss of surface function, seen in the homorhabdic filibranchs studied; (2) reduction of cilia but retention or increase in acid mucopolysaccharide-secreting (AMPS) mucocyte density in the eulamellibranchs, corresponding to the assumption of a new function, probably in the reduction of frictional resistance to flow in the water canals. Heterorhabdic gill abfrontal surfaces present a mixture of these characteristics: reduction of cilia and mucocytes on the ordinary filaments, and retention of both on the principal filaments. The retention of AMPS mucocytes on the abfrontal surface of the pseudolamellibranchs may be related to the degree of interlamellar fusion, reducing frictional resistance to water flow as in the eulamellibranchs. The gill abfrontal surface thus constitutes an excellent candidate for the study of the different evolutionary options and trajectories of a redundant feature.

Abstract The dorsal ligaments of arcoid bivalves typically consist of oblique, lamellar and fibrous sheets, alternating along the hinge so that their attachments form characteristic chevron patterns. New elements are added at or near the middle of the pattern, as the ligament grows ventrally and gets longer. Most Palaeozoic arcoids exhibit this growth pattern, which still predominates among their living descendants. Early in the Cretaceous, a novel pattern emerged, with vertical strips of lamellar ligament embedded in grooves in the sheet of fibrous ligament which is attached to each valve. In contrast with the chevron, duplivincular ligament, new elements are added to each end of the noetiid ligament, anteriorly and posteriorly. This distinctive growth pattern is the defining character of the family Noetiidae. Remarkable variation among individuals within populations of a living limopsid arcoid includes forms with vertical strips of lamellar ligament. These variants suggest how the noetiid growth pattern could have been derived from the duplivincular pattern. Computer simulations show that such patterns can be generated by a reaction–diffusion mechanism of the sort first conceived by Turing ( 1952 , Philosophical Transactions of the Royal Society, London, Series B, 237, 37–72). Moreover, the noetiid growth pattern can simply be derived from the duplivincular pattern by a developmental switch based, for example, on a change in boundary conditions. These results indicate that striking differences in form may arise from modest changes in the developmental process. The evolution of the Noetiidae, members of which are quite disparate in overall shell form, should be reassessed. The derived character on which this family is based may not be uniquely shared, so the group could well be polyphyletic.

Abstract Unusual Pennsylvanian bivalves recovered from the Buckhorn Asphalt Quarry of south-central Oklahoma are members of the Order Praecardioida, Family Lunulacardiidae. This is the youngest occurrence of praecardioids in North America. These praecardioids have an ontogeny characterized by a veneriform juvenile shell, changing abruptly to an elongate adult shell with sharp carinae, accompanied by strong rotation of the juvenile shell and change in ligament. These shells provide new evidence of dentition and ligament for lunulacardiids and the first documentation of praecardioid shell microstructure. The Buckhorn taxa possess stout hinge teeth, indicating that lunulacardiids are not edentulous. Preserved ligament in multiple growth stages indicates that beaks are prosogyrous and the flattened truncated portion of the shell is posterior. A revised diagnosis of the Lunulacardiidae is presented. New taxa: Buckhornia carteri n. gen., n. sp.