Species of the marine bivalve family Laternulidae are frequently misidentified with some having particularly tangled nomenclatural histories. To redress these problems all available type specimens or new images of them, totalling 52 of the 56 nominal species, were examined and assessed. Concurrently, new molecular analyses identified major clades and corroborated species boundaries based on shell characters. Two clades of laternulids were recognised as subfamilies Laternulinae and Exolaternulinae the latter introduced herein and characterised by presence of a lithodesma. A new classification of the family is presented. The depth of insertion of the pallial sinus is identified as a useful character separating species with similar shell shapes. Two new genera Cryolaternula and Parilaternula are proposed. Twenty-eight putative species are recognised with some resurrected from prior synonymy. Six new species are described: Laternula pristissinus Taylor & Glover, L. inopinata Taylor & Glover, L. omissa Taylor & Glover, Parilaternula acuta Taylor, Fukuda & Haga, P. certa Taylor & Glover and P. delicata Taylor, Glover & Hong. To stabilise the name Exolaternula a lectotype is selected for the type species, Anatina truncata Lamarck, 1818. Exolaternulinae species are distributed from the Arabian Gulf eastwards to Japan and eastern Russia and northern Australia at the southern limit. Laternulinae species occur around Australia, northern Indian Ocean, through the central Indo-W. Pacific to Japan, with Cryolaternula confined to the Southern Ocean within the Antarctic Convergence.

Phosphate mineralization as a skeletal material is uncommon in invertebrate animals and rare in Mollusca. Remarkably, apatite minerals were first reported more than 30 years ago in the periostracum of two species of the mytilid bivalve Lithophaga where shells are mostly constructed of calcium carbonate. This discovery extended the range of biominerals secreted by molluscs but has attracted no subsequent research. In this study we review the occurrence of phosphate mineralization in Lithophaga and putatively allied taxa. Lithophagine bivalves, particularly Lithophaga and the more diverse Leiosolenus species, are well known for their endolithic chemical dissolution of calcareous rocks and corals with calcium-binding lipoproteins secreted by mantle glands. Fluorapatite was identified by X-ray diffraction in an outer layer of the periostracum in six species of Lithophaga. Morphological study by scanning electron microscopy of four species showed the fluorapatite crystals embedded in periostracal material in a layer 10-20 mu m thick. Dilute bleach treatment revealed the crystals as densely packed euhedral prisms 250-400 nm in size. The succeeding inner layers of the periostracum were unmineralized. Observations of the developing periostracum of Lithophaga teres suggest that the initial mineralization is in the form of amorphous granules that coalesce and transform into euhedral crystals. Periostracal phosphate was not recorded in other members of the Lithophaginae - Leiosolenus, Botula or Zelithophaga species. Leiosolenus species characteristically have extraperiostracal aragonitic encrustations that can be thick and structurally complex. Published molecular phylogenies of Mytilidae bivalves show a division into two major clades with Lithophaga species in one clade and Leiosolenus species in the other, indicating that the subfamily Lithophaginae as presently understood is polyphyletic. This result implies that the two genera have independent evolutionary pathways to endolithic occupation of calcareous substrates although using similar mantle gland secretions to excavate their crypts. Because fluorapatite is considerably less soluble and harder than calcium carbonate, it is suggested that the phosphate layer of Lithophaga is a functional adaptation to protect their shells from self-dissolution from their rock-dissolving glandular secretions and may also act as defence against other shell-eroding organisms.

New molecular phylogenies of the chemosymbiotic bivalve family Lucinidae, using 18S rRNA, 28S rRNA and cytochrome b genes, include species from genera not previously analysed. Notable additions from Myrteinae are sequences from Rostrilucina, Solelucina and Taylorina species, species of Ustalucina, Gonimyrtea from Leucosphaerinae and additional species of Ctena, Codakia, Lucinoma and Divalucina from Codakiinae. New sequences of Lucininae include the type species of Parvilucina (P. tenuisculpta), Liralucina, Falsolucinoma, Easmithia, Jallenia, Radiolucina and Cardiolucina as well as samples of Loripes orbiculatus from multiple localities. Five major clades, defined as subfamilies, are recognized: Pegophyseminae, Myrteinae, Leucosphaerinae, Codakiinae and Lucininae. Two branches, Fimbriinae and Monitilorinae, are represented by single species. Pegophyseminae are an extremely long-branched group with a sister-group relationship to Leucosphaerinae, while Codakiinae are a sister clade to the Lucininae. In various gene trees, the position of Myrteinae is unstable in relation to Pegophyseminae + Leucosphaerinae, Monitilorinae and Fimbriinae. The Myrteinae are not well resolved, with an ambiguous correlation of molecular and morphological characters. Codakiinae now include Divalucina cumingi, shown to be related to Lucinoma rather than Divaricella and Divalinga of the Lucininae. Leucosphaerinae are a well-supported clade but morphologically disparate, with the positions of Gonimyrtea and Callucina unresolved. Several molecularly distinct subclades are recognized within the Lucininae, especially the Lucinisca, Loripes and Parvilucina groups. Parvilucina species are paraphyletic with P. tenuisculpta, the type species, distinct from the western Atlantic species. Codakia, Ctena and Pegophysema have pan-tropical distributions with former connections disrupted by vicariant events of the closure of the eastern Tethyan and Central American Seaways. Species of Radiolucina, Pleurolucina and Lucinisca are present on either side of the Isthmus of Panama. A new classification of the 96 living lucinid genera is presented, providing a framework for future studies of systematics, ecology, biogeography and bacterial symbioses.

Species identified as Pillucina are paraphyletic in molecular analyses and a new generic name, Rugalucina, is introduced for a complex of three similar species Rugalucina angela from the northern Indian Ocean and Red Sea, R. vietnamica from South East Asia, and R. munda from northern and north eastern Australia. Lucina concinna from the Red Sea, previously synonymised with P. vietnamica/angela is recognised as a Rugalucina-like species but with a very short anterior adductor scar. Divaricella cypselis from Karachi is similarly now recognised as a distinct species, probably related to Rugalucina but with oblique commarginal sculpture and a short adductor scar. A group of minute Indo-West Pacific lucinids with highly unusual multi-cuspate lateral teeth and previously classified as Pillucina are separated under a new genus Pusillolucinagen. nov., with the description of three new species P. arabica, P. africana, and P. biritika from the Arabian Gulf, Mozambique, and Madagascar. Finally, a new genus, Notocina, is introduced for the small southern Atlantic species, Epicodakia falklandica, shown in molecular analyses to be misplaced at subfamily level and now classified in Lucininae and not Codakiinae with Epicodakia.

The large, burrowing bivalve Laternula elliptica is an abundant component of shallow-water soft-substrate communities around Antarctica but its congeners are temperate and tropical in distribution and their phylogenetic relationships are obscure. A new molecular analysis of Laternulidae species shows that there are two distinct clades, one of Exolaternula species, E. spengleri and E. liautaudi, possessing a ligamental lithodesma and a larger clade of species lacking the lithodesma. Of the latter, Laternula elliptica is a sister taxon to temperate and tropical species, including those that live around the coasts of Australia from Tasmania to Darwin. It is suggested that L. elliptica was left isolated around Antarctica following the opening of the Tasman Gateway and initiation of the Circum-Antarctic Current as Australia drifted northwards following the final breakup of Gondwana. A further scenario is that as Australia moved closer to Asia, species spread into tropical habitats and more widely to the Red Sea and Japan. Exolaternula species have a likely Tethyan origin and the present-day range is from the Arabian Gulf, around southern Asia and as far north as southern Russia.

Rare species of three long-lived lucinid genera, Gibbolucina Cossmann, 1904, Barbierella Chavan, 1938 and Retrolucina n. gen., with origins in the Paleocene and Eocene of western Tethys, are present in the Mozambique Channel area of the southwestern Indian Ocean but absent elsewhere in the Indo-West Pacific. A new species, Gibbolucina zelee n. sp., is described from the Banc de la Zelee and western Madagascar that resembles Miocene species from western France. Since their origin in the Paleocene to the present day Barbierella species have always been rare. New records and images, including syntypes, are provided for Barbierella louisensis (Viader, 1951) from Mauritius and the Mozambique Channel, with Barbierella scitula Oliver & Abou-Zeid, 1986 from the Red Sea regarded as synonym. A new genus, Retrolucina n. gen., is proposed with the living Lucina voorhoevei Deshayes, 1857 (usually called Eomiltha voorhoevei) as type species and also including Lucina defrancei Deshayes, 1857, a strikingly similar species from the Eocene of the Paris Basin. Retrolucina n. gen. differs from Eomiltha Cossmann, 1912 in shape, sculpture and hinge characters. Monitilora Iredale, 1930, another genus of Paleocene or earlier origins, includes a few living species in the Indo-West Pacific and is now identified from Mozambique with Monitilora sepes (Barnard, 1964) (formerly Phacoides sepes Barnard, 1964). It is suggested that Gibbolucina, Barbierella and Retrolucina n. gen. species became isolated in the western Indian Ocean following the closure of the Tethyan Seaway in the early Miocene while their congeners in western Tethys became extinct. The survival of these rare genera, with restricted geographical ranges and seemingly small populations, runs counter to current ideas concerning long-term extinction risk.

A new species of the lucinid bivalve genus Lucinoma is described from shells dredged at depths of 240-500 m from the edge of the continental shelf off southern Newfoundland. It differs from the other northern species, Lucinoma filosa, in shape, ligament, and characters of the anterior adductor muscle scar. It also differs from the poorly known Lucinoma atlantis from the outer shelf off Maryland that is longer than high and has both anterior and posterior sulci, and from L. blakeana from deep water off North Carolina, a smaller species with a truncate posterior margin. Other Lucinoma species are recorded further south in the northern Gulf of Mexico, particularly from hydrocarbon seeps, although the taxonomy is confused for those taxa.

The systematics of the molluscan class Bivalvia are explored using a 5-gene Sanger-based approach including the largest taxon sampling to date, encompassing 219 ingroup species spanning 93 (or 82%) of the 113 currently accepted bivalve families. This study was designed to populate the bivalve Tree of Life at the family level and to place many genera into a clear phylogenetic context, but also pointing to several major clades where taxonomic work is sorely needed. Despite not recovering monophyly of Bivalvia or Protobranchia-as in most previous Sanger-based approaches to bivalve phylogeny-our study provides increased resolution in many higher-level clades, and supports the monophyly of Autobranchia, Pteriomorphia, Heteroconchia, Palaeoheterodonta, Heterodonta, Archiheterodonta, Euheterodonta, Anomalodesmata, Imparidentia, and Neoheterodontei, in addition to many other lower clades. However, deep nodes within some of these clades, especially Pteriomorphia and Imparidentia, could not be resolved with confidence. In addition, many families are not supported, and several are supported as non-monophyletic, including Malletiidae, Nuculanidae, Yoldiidae, Malleidae, Pteriidae, Arcidae, Propeamussiidae, Iridinidae, Carditidae, Myochamidae, Lyonsiidae, Pandoridae, Montacutidae, Galeommatidae, Tellinidae, Semelidae, Psammobiidae, Donacidae, Mactridae, and Cyrenidae; Veneridae is paraphyletic with respect to Chamidae, although this result appears to be an artifact. The denser sampling however allowed testing specific placement of species, showing, for example, that the unusual Australian Plebidonax deltoides is not a member of Donacidae and instead nests within Psammobiidae, suggesting that major revision of Tellinoidea may be required. We also showed that Cleidothaerus is sister group to the cementing member of Myochamidae, suggesting that Cleidothaeridae may not be a valid family and that cementation in Cleidothaerus and Myochama may have had a single origin. These results highlight the need for an integrative approach including as many genera as possible, and that the monophyly and relationships of many families require detailed reassessment. NGS approaches may be able to resolve the most recalcitrant nodes in the near future.

Intensive sampling of molluscs from the intertidal to depths of 800 m around the islands of Guadeloupe in the Lesser Antilles (KARUBENTHOS 2012, 2015) recovered 25 species of Lucinidae. All the Guadeloupe species are described and illustrated including details of larval shells and the taxonomy revised within the context of the wider western Atlantic fauna and recent classifications. Concurrent molecular analysis has helped separate frequently confounded species. 'Myrtea' pristiphora is placed in the Leucosphaerine genus Myrtina previously known from the Indo-West Pacific. A second western Atlantic species of Callucina, C. pauperatus previously known from the Pliocene of Jamaica is recognised from the southern Caribbean and off Brazil. The deeper water species 'Myrteopis' lens is placed in Afrolucina previously known from the eastern Atlantic. Lucinids commonly identified as Ctena orbiculata are shown to belong to two distinct species, C. orbiculata in the Gulf of Mexico and Florida and C. imbricatula in the Caribbean. Epicodakia is recognised for the first time in the western Atlantic with E. pectinata widely distributed across the region and E. filiata recorded from deeper water. Three species of Lucina are recognised, Lucina pensylvanica in the Gulf of Mexico and Florida and the similar Lucina roquesana from the Caribbean and Bahamas while the smaller L. aurantia has a wide distribution from central America to the Bahamas. A new species of Parvilucina, P. latens is described; this is similar to P. pectinella but has an internal ligament. The long problematic species 'Codakia' cubana is assigned to Ferrocina. A new genus, Guyanella is introduced for Parvilucina clenchi the smallest known lucinid. A critical reassessment of the lucinid fauna of the western Atlantic Ocean identifies 46 species for the region with 33 of these living at depths less than 200 m. Deeper-water habitats have been much less investigated except at sites of hydrocarbon seeps. Some species are widespread throught the whole region but others have more restricted ranges. Notable are species pairs, for example of Ctena, Lucina, Lucinisca and Parvilucina that are either largely Caribbean or Gulf of Mexico/Floridian in distribution. Although extralimital, two problematic species from the mid-south Atlantic island of St Helena are refigured and placed in Cavilinga.

A new molecular phylogeny of the Lucinidae using 18S and 28S rRNA and cytochrome b genes includes many species from the tropical Western Atlantic as well as additional taxa from the Indo-West Pacific. This study provides a phylogenetic framework for a new taxonomy of tropical Western Atlantic lucinids. The analysis confirmed five major clades-Pegophyseminae, Leucosphaerinae, Myrteinae, Codakiinae and Lucininae, with Monitilorinae and Fimbriinae represented by single species. The Leucosphaerinae are expanded and include Callucina winckworthi and the W. Atlantic Myrtina pristiphora that groups with several Indo-West Pacific Myrtina species. Within the Codakiinae two abundant species of Ctena from the Western Atlantic with similar shells are discriminated as C. orbiculata and C. imbricatula, while in the Indo-West Pacific Ctena bella is a probable species complex. The Lucininae is the most species rich and disparate subfamily with several subclades apparent. Three species of Lucina are recognized in the W. Atlantic L. aurantia, L. pensylvanica and L. roquesana. Pleurolucina groups near to Cavilinga and Lucina, while Lucinisca muricata is more closely related to the E. Pacific L. fenestrata than to the Atlantic L. nassula. A new species of Parvilucina is identified from molecular analyses having been confounded with Parvilucina pectinata but differs in ligament structure. Also, the former Parvilucina clenchi is more distant and assigned to Guyanella.

A new shallow water species of the lucinid bivalve Pleurolucina is described from Curaçao in the southern Caribbean Sea and compared with known species of the genus from the western Atlantic and eastern Pacific Oceans. Although confused with the Floridian species P. leucocyma, it is most similar to the eastern Pacific P. undata. As in all studied lucinids, the new species possesses symbiotic bacteria housed in the ctenidia. The shell microstructure is unusual with repeated and intercalated conchiolin layers that have sublayers of ‘tulip-shaped’ calcareous spherules. Predatory drillings by naticid gastropods frequently terminate at the conchiolin layers.

A survey of the lucinid bivalves of Singapore recorded 18 species, 12 of these located during the Singapore Strait Biodiversity Workshop, two others previously collected from the Straits of Johor and a further four species identified from museum specimens. These are illustrated and briefly described. In 2013 survey, lucinids were uncommon at most locations but a seagrass bed at the southern end of the artificially constructed beach joining Seringat and Lazarus islands, yielded 9 species of lucinids and numerous other infaunal bivalves. By far the most abundant species was the small Pillucina profusa, with fewer numbers of Euanodontia ovum, Cardiolucina macassari, Cavatidens bullula, Leucosphaera philippinensis and Liralucina lyngei. The associated infaunal bivalves included 36 species from 10 families; the most diverse were Tellinidae with 14 species and these are illustrated to assist local identification. Three lucinids, Austriella corrugata, Indoaustriella dalli, and Pegophysema philippiana occurred amongst mangroves in the Strait of Johor. Species for which only museum records are available, such as Codakia paytenorum and Lepidolucina venusta, may be locally extinct. Five Singapore lucinid species were included in a new molecular analysis (18S, 28S and cytochrome b genes) to establish their phylogenetic relationships and anatomical details including, in particular, ctenidial structure and morphology of bacterial symbionts for Eunanodontia ovum and Pillucina profusa.

To re-evaluate the relationships of the major bivalve lineages, we amassed detailed morpho-anatomical, ultrastructural and molecular sequence data for a targeted selection of exemplar bivalves spanning the phylogenetic diversity of the class. We included molecular data for 103 bivalve species (up to five markers) and also analysed a subset of taxa with four additional nuclear protein-encoding genes. Novel as well as historically employed morphological characters were explored, and we systematically disassembled widely used descriptors such as gill and stomach ‘types’. Phylogenetic analyses, conducted using parsimony direct optimisation and probabilistic methods on static alignments (maximum likelihood and Bayesian inference) of the molecular data, both alone and in combination with morphological characters, offer a robust test of bivalve relationships. A calibrated phylogeny also provided insights into the tempo of bivalve evolution. Finally, an analysis of the informativeness of morphological characters showed that sperm ultrastructure characters are among the best morphological features to diagnose bivalve clades, followed by characters of the shell, including its microstructure. Our study found support for monophyly of most broadly recognised higher bivalve taxa, although support was not uniform for Protobranchia. However, monophyly of the bivalves with protobranchiate gills was the best-supported hypothesis with incremental morphological and/or molecular sequence data. Autobranchia, Pteriomorphia, Heteroconchia, Palaeoheterodonta, Archiheterodonta, Euheterodonta, Anomalodesmata and Imparidentia new clade ( = Euheterodonta excluding Anomalodesmata) were recovered across analyses, irrespective of data treatment or analytical framework. Another clade supported by our analyses but not formally recognised in the literature includes Palaeoheterodonta and Archiheterodonta, which emerged under multiple analytical conditions. The origin and diversification of each of these major clades is Cambrian or Ordovician, except for Archiheterodonta, which diverged from Palaeoheterodonta during the Cambrian, but diversified during the Mesozoic. Although the radiation of some lineages was shifted towards the Palaeozoic (Pteriomorphia, Anomalodesmata), or presented a gap between origin and diversification (Archiheterodonta, Unionida), Imparidentia showed steady diversification through the Palaeozoic and Mesozoic. Finally, a classification system with six major monophyletic lineages is proposed to comprise modern Bivalvia: Protobranchia, Pteriomorphia, Palaeoheterodonta, Archiheterodonta, Anomalodesmata and Imparidentia.