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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 Pleurolucina leucocyma, it is most similar to the eastern Pacific Pleurolucina 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.

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 Pusillolucina gen. 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 .

Four new species and a new genus of lucinid bivalves are described from shallow and deeper waters in the Indian and West Pacific Oceans. The new genus Scabrilucina (subfamily Lucininae) includes the little-known S. victorialis (Melvill, 1899) from the Arabian Sea and S. vitrea (Deshayes, 1844) from the Andaman Sea as well as a new species S. melvilli from the Torres Strait off northeastern Australia. Ferrocina brunei new species (Lucininae) was recovered from 60 m near oil drilling activities off Borneo; its anatomy confirmed the presence of symbiotic bacteria. Two unusual deeper water species of Leucosphaerinae are described, both species included in on-going molecular analyses; Gonimyrtea ferruginea from 400–650 m in the southwest Pacific and Myrtina reflexa from 200–825 m off Zanzibar and Madagascar.

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.

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.

A new molecular phylogeny of the chemosymbiotic bivalve family Lucinidae is presented. Using sequences from the nuclear 18S and 28S rRNA genes and the mitochondrial gene cytochrome b, 105 specimens were analysed representing 87 separate species classified into 47 genera. Samples were collected from a wide range of habitats including mangroves, seagrass beds, shallow sands, offshore muds, and hydrocarbon seeps at depths ranging from the intertidal to over 2000 m. A chronogram, derived from the combined molecular tree, was calibrated using ten lucinid fossils. The trees show five well-supported clades and two single branches of Fimbria fimbriata (Linnaeus, 1758) and Monitilora ramsayi (Smith, 1885). A new classification of Lucinidae is proposed with seven subfamilial divisions: three new subfamilies ‐ Pegophyseminae, Leucosphaerinae, and Monitilorinae ‐ are introduced and Codakiinae, usually treated as a synonym of Lucininae, is revived to include the Lucinoma, Codakia, and Ctena subclades. Membership of the Lucininae and Myrteinae is considerably revised compared with Chavan’s commonly employed ‘Treatise’ classification. Previously considered as a separate family, Fimbriinae is now regarded as a subfamily within Lucinidae. The status of Milthinae is presently equivocal pending further analysis and Divaricellinae is recognized as polyphyletic, and is therefore abandoned, with species and genera now grouped in various places within the Lucininae. Deeper water Lucinidae mainly belong to Leucosphaerinae, Codakiinae (Lucinoma clade), and Myrteinae, with Lucinoma species being most frequently associated with hydrocarbon seeps. Species occurring in seagrass habitats derive largely from Pegophyseminae, Codakiinae, and Lucininae, and species from mangrove habitats derive from the Pegophyseminae and Lucininae.

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 Zélée 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., Des espèces rares appartenant à trois genres anciens de lucines, Gibbolucina Cossmann, 1904, Barbierella Chavan, 1938 et Retrolucina n. gen., dont l'origine se situe au Paléocène et à l'Éocène en Téthys occidentale, sont présentes dans la zone du Canal du Mozambique dans le sud-ouest de l'océan Indien, et absentes ailleurs dans l'Indo-Ouest Pacifique. Une nouvelle espèce, Gibbolucina zelee n. sp., est décrite du Banc de la Zélée et de l'ouest de Madagascar; elle ressemble à une espèce du Miocène de l'ouest de la France. Depuis leur origine au Paléocène jusqu'à nos jours, les espèces de Barbierella ont toujours été rares. Des signalisations nouvelles et des illustrations, dont celles de syntypes, sont données pour Barbierella louisensis (Viader, 1951) de l'île Maurice et du Canal du Mozambique, et Barbierella scitula Oliver & Abou-Zeid, 1986 de la Mer Rouge est donnée comme synonyme. Le nouveau genre Retrolucina n. gen. est établi avec pour espèce type l'espèce actuelle Lucina voorhoevei Deshayes, 1857 (habituellement appelée Eomiltha voorhoevei), et comprenant également Lucina defrancei Deshayes, 1857, une espèce de l'Éocène du Bassin Parisien qui lui est étonnamment semblable. Retrolucina n. gen. diffère d'Eomiltha Cossmann, 1912 par sa forme, sa sculpture et les caractères de sa charnière. Monitilora sepes (Barnard, 1964), du Mozambique (auparavant Phacoides sepes Barnard, 1964), est classée dans le genre Monitilora Iredale, 1930, un autre genre dont l'origine remonte au moins au Paléocène et qui comprend un petit nombre d'espèces actuelles de l'Indo-Ouest Pacifique. Les espèces de Gibbolucina, Barbierella et Retrolucina n. gen. ont pu se retrouver isolées dans l'Ouest de l'océan Indien à la suite de la fermeture de la Téthys au début du Miocène alors que leurs congénères de la Téthys occidentale se sont éteintes. La survie de ces genres rares, avec des aires de distribution restreintes et apparemment de petites populations, va à l'encontre des idées classiques sur les risques d'extinction à long terme.

A scanning electron microscope study of the periostracum of 50 species of venerid bivalves revealed that periostracal calcification in the form of aragonitic needles and shorter pins is widespread within the family. Together with organic and sediment coatings that are found in some species, these needles form an integral part of the functional shell. Visible as a white ‘crust’ on the outside of shells, long slender needles (up to 400 mm long and 1 mm wide) without adherent material are seen in species of Tivela and Lioconcha and in Gomphina undulosa. Other venerids including Pitar species, Mysia undata and Compsomyax subdiaphana have short pins, capped with a fibrous organic matrix and significant coatings of sediment. Callocardia hungerfordi and Clementia papyracea have very thick sediment coatings underlain by short pins, while Gafrarium and Circe species have short pins with a thin, robust, organic coating and little particulate material. Finally, there are species, including Venus verrucosa, Chione elevata and Mercenaria mercenaria, where minute, ,1 mm long pins also underpin a thin organic coating. Details of formation were studied in Tivela lamyi and Lioconcha ornata, where the needles are elongate hexagonal crystals of aragonite enveloped by an organic sheath, which grow at their proximal ends from within the periostracum, connected to the outer mantle epithelium via narrow channels. Growth of needles ceases following the onset of shell calcification. The distribution of the periostracal structures was examined in relation to a published molecular phylogeny that recognized two major clades within the family. Larger needles and pins are confined to the clade that includes subfamilies Pitarinae, Gouldinae, Meretricinae and Petricolinae, while submicron-sized pins are found only in the Venerinae and Chioninae of the second clade. Calcified periostracal structures appear to be absent in Tapetinae and Dosiniinae.

The structure of the ctenidia of the Indo-West Pacific chemosymbiotic lucinid bivalve Anodontia (Euanodontia) ovum was investigated by electron microscopy. Ctenidial filaments are similar in general morphology to those described from other Lucinidae, with a ciliated zone, a short intermediary zone and a thick abfrontal zone composed largely of bacteriocytes separated by narrow intercalary cells. The bacteriocyte zones of adjacent filaments are fused in the distal part to form short cylindrical channels. The apices of intercalary cells project as cytoplasmic protrusions in the form of spiky tufts, with sheets and tendrils spreading over adjacent bacteriocytes. Compared with other lucinids A. ovum lacks abfrontal granule cells, mucocytes are infrequent and the bacteriocyte channels are short. Three morphotypes of symbiotic bacteria were detected, associated with the bacteriocyte zone of the ctenidial filaments: (1) all bacteriocytes contained abundant bacteria 3-5 mu m long and 0.5-1.0 mu m wide, enclosed in single vacuoles; (2) some bacteriocytes possessed spherical vesicles enclosing masses of smaller rod-shaped bacteria c. 1.0 mu m long; (3) probable spirochaete bacteria, 8-10 mu m long and 0.3 mu m wide, were abundant within the apical cytoplasmic protrusions of the intercalary cells. Preliminary molecular analysis using 16S rRNA gene sequences has so far identified only one bacterial symbiont, from the gamma division of Proteobacteria grouping in a cluster of symbiotic thiotrophs. This symbiont of A. ovum is closely similar to a symbiont previously reported from the western Atlantic lucinid Anodontia schrammi (originally cited as A. philippiana).

The giant bivalve Lucina megameris Dall, 1901, from the late Eocene White Limestone Group of Jamaica and by far the largest known species of the family Lucinidae, is placed in a new genus Superlucina. Apart from its large size, with a shell height exceeding 310 mm, it is distinguished from other genera, such as Pseudomiltha and Eomiltha by external shell characters and the extremely long and narrow, anterior adductor muscle scar. Features preserved on internal moulds suggest that, in common with living Lucinidae, S. megameris was chemosymbiotic with sulphide - oxidizing bacteria housed in the gills. Palaeoenvironmental evidence suggests a habitat in oligotrophic, shallow waters, probably in seagrass beds, with an associated molluscan fauna includ- ing large cardiids that may have been photosymbiotic. Super- lucina is considerably larger than any living lucinid that range in size from 3 to 150 mm with most encompassed within 5-30 mm. From the Jurassic onwards, a few other large lucinids are known from cold seep sites, with several other records from possible shallow water seagrass beds.

Recent molecular analyses have demonstrated that the traditional Lucinoidea, comprising the extant families Lucinidae, Thyasiridae, Ungulinidae, Fimbriidae, and Cyrenoididae, is not monophyletic. Thyasiridae and Ungulinidae are unrelated to Lucinidae, a result corroborated by clear morphological differences between the groups. Chemosymbiosis in Thyasiridae and Lucinidae has been independently derived. Within the family Lucinidae, previous ideas of relationship and subfamilial divisions based on shell characters have little support from molecular results. Anatomical characters of the ctenidia, mantle gills, and posterior apertures have potential in phylogenetic analysis but rigorous analysis of shell characters is also needed. Although there is a good fossil record of Lucinidae throughout the Cenozoic and Mesozoic, in the Palaeozoic fossils are less frequent and most need reappraisal. The Silurian Ilionia prisca is probably the earliest fossil with convincing lucinid features, followed in the Devonian by Phenacocyclas and some Paracyclas species. © 2006 The Linnean Society of London, Zoological Journal of the Linnean Society, 2006, 148, 421–438.

This taxonomic revision concerns the Australian and Indo-Pacific species of small lucinid bivalves possessing a deeply inset internal ligament. Nine species of Pillucina are recognised of which four occur around Australia including the two new species, P. pacifica and P. australis. Two other new species are described; P. denticula from South Africa and P. mauritiana from Mauritius. Pillucina vietnamica is common along the Queensland coast and P. symbolica the only species previously recorded from Australia is considered conspecific with the wide ranging species P. pisidium. A new genus, Chavania, includes two species; C. striata is widely distributed in the Indo-West Pacific including eastern and western Australia, while C. erythraea is restricted to the Arabian Peninsula. Two species of Wallucina live around Australia, W. assimilis is endemic occurring at southerly locations from New South Wales to North West Cape, while the tropical species, W. fijiensis, is found in island habitats of Queensland but is widely distributed in the Indo-West Pacific. Another new genus, Funafutia, is proposed for the species, F. levukana, recorded from Australia for the first time. Details of anatomy are provided for Pillucina vietnamica, W. assimilis and C. striata. Symbiotic bacteria are confirmed for the first time in the lateral zone of gill filaments of Pillucina vietnamica and Wallucina assimilis.

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 .

Revived interest in molluscan phylogeny has resulted in a torrent of molecular sequence data from phylogenetic, mitogenomic, and phylogenomic studies. Despite recent progress, basal relationships of the class Bivalvia remain contentious, owing to conflicting morphological and molecular hypotheses. Marked incongruity of phylogenetic signal in datasets heavily represented by nuclear ribosomal genes versus mitochondrial genes has also impeded consensus on the type of molecular data best suited for investigating bivalve relationships. To arbitrate conflicting phylogenetic hypotheses, we evaluated the utility of four nuclear protein-encoding genes—ATP synthase β, elongation factor-1α, myosin heavy chain type II, and RNA polymerase II—for resolving the basal relationships of Bivalvia. We sampled all five major lineages of bivalves (Archiheterodonta, Euheterodonta [including Anomalodesmata], Palaeoheterodonta, Protobranchia, and Pteriomorphia) and inferred relationships using maximum likelihood and Bayesian approaches. To investigate the robustness of the phylogenetic signal embedded in the data, we implemented additional datasets wherein length variability and/or third codon positions were eliminated. Results obtained include (a) the clade (Nuculanida + Opponobranchia), i.e., the traditionally defined Protobranchia; (b) the monophyly of Pteriomorphia; (c) the clade (Archiheterodonta + Palaeoheterodonta); (d) the monophyly of the traditionally defined Euheterodonta (including Anomalodesmata); and (e) the monophyly of Heteroconchia, i.e., (Palaeoheterodonta + Archiheterodonta + Euheterodonta). The stability of the basal tree topology to dataset manipulation is indicative of signal robustness in these four genes. The inferred tree topology corresponds closely to those obtained by datasets dominated by nuclear ribosomal genes (18S rRNA and 28S rRNA), controverting recent taxonomic actions based solely upon mitochondrial gene phylogenies.