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Reduction in body size of organisms following mass extinctions is well‐known and often ascribed to the Lilliput effect. This phenomenon is expressed as a temporary body size reduction within surviving species. Despite its wide usage the term is often loosely applied to any small post‐extinction taxa. Here we assess the size of bivalves of the family Limidae (Rafineque) prior to, and in the aftermath of, the end‐Triassic mass extinction event. Of the species studied only one occurs prior to the extinction event, though is too scarce to test for the Lilliput effect. Instead, newly evolved species originate at small body sizes and undergo a within‐species size increase, most dramatically demonstrated by Plagiostoma giganteum (Sowerby) which, over two million years, increases in size by 179%. This trend is seen in both field and museum collections. We term this within‐species size increase of newly originated species in the aftermath of mass extinction, the Brobdingnag effect, after the giants that were contemporary with the Lilliputians in Swift's Gulliver's Travels. The size increase results from greater longevity and faster growth rates. The cause of the effect is unclear, although it probably relates to improved environmental conditions. Oxygen‐poor conditions in the Early Jurassic are associated with populations of smaller body size caused by elevated juvenile mortality but these are local/regional effects that do not alter the long‐term, size increase. Although temperature‐size relationships exist for many organisms (Temperature‐Size Rule and Bergmann's Rule), the importance of this is unclear here because of a poorly known Early Jurassic temperature record.

Two new bivalve genera and three new species of the family Limidae from the Upper Eocene of Ukraine are described.

One of the most well-known species in the bivalve family Limidae (d’Orbigny, 1846) is the brightly coloredCtenoides scaber(Born, 1778), commonly known as the rough file clam or flame scallop. Distinguishing this bivalve from its close relative,C. mitis(Lamarck, 1807), can be difficult using only morphological features and has led to much taxonomic confusion throughout the literature. In this study, morphological characters were compared to a molecular phylogeny constructed using three genes (COI, 28S, and H3) in order to differentiateC. scaberandC. mitis.The phylogeny recovered two well-supported clades that differ significantly in shell rib numbers, but not tentacle colors. The two species were then placed in a larger phylogenetic context of the Limidae family, which revealed the need for further systematic revision across genera. As these bivalves are popular in aquaria, cannot be tank-raised, and have been overcollected in the past, proper species identification is important for assessing sustainable collection practices.

We have compiled a complete list of new marine molluscan taxa introduced by Tommaso Allery Di Maria, Marquis of Monterosato (1841–1927). The dates of publication of every single work have been checked against available evidence, and an updated bibliography is also presented. Finally, the type material of all marine taxa expected to be in the collection Monterosato (presently preserved in the Museo Civico di Zoologia in Rome) has been searched in the main collection, and all retrieved specimens have been catalogued. A large majority of the material has been found, representative specimens of each taxon have been illustrated, and remarks on nomenclature and taxonomy have been provided yielding 42 new synonymies, 46 nominal taxa rediscovered, and 6 new combinations.

In order to enhance the understanding of Pacific Colombia’s deep-water marine fauna, a benthic research cruise (2012 TUM Offshore 6 and 7) was conducted off the coast of the Department of Nariño, in southern Colombia. Biological, oceanographic and sediment samples from the continental shelf and slope were collected at depths between 350 and 941 m. A new species of Malletia obtained on that cruise is described and compared with other species from the eastern Pacific. Sixteen species of bivalve mollusks (belonging to 12 families and 15 genera) were identified. Five of them were the first records for Pacific Colombia (Jupiterialobula, Limatulasaturna, Lucinomaheroica, Cuspidariapanamensis, and Dallicordiaalaskana). Four of them had geographic distributions that now extend to Tumaco at the southern end of Nariño.

Mantellina translucens n. sp. inhabits the deep reefs (215-310 m) off southeastern Curacao, occurring singly or in pairs, attached to vertical rock walls and boulders by thin byssal threads. This species differs from all living Limidae in having an exceptionally thin, comarginally corrugated shell that is longer than tall and lacks radial sculpture. This new species possesses a unique suite of characters associated with adaptations to an epibyssate mode of life in bathyal habitats, including simplification of the digest- ive tract, possibly indicating omnivory. It is assigned to the genus Mantellina Sacco, 1904, previously known only from fossil deposits of Burdigalian to Serravallian Miocene age of the Central Paratethys, on the basis of similar shell morphology. Anatomical characters and ribosomal DNA sequence data (18S and 16S genes) confirm placement of this taxon within the family Limidae, yet its shell superficial- ly resembles those of several genera of the extinct family Inoceramidae, while differing in hinge morph- ology and shell ultrastructure. A preliminary molecular phylogeny recovered Limidae as a monophyletic clade within Pteriomorphia, with Mantellina derived relative to Limaria, and sister group to a clade containing the remaining representatives of Limidae. Ctenoides was not monophyletic. The phylogenetic tree based on molecular data does not support previously proposed suprageneric relation- ships based on morphological data.

The structure of the spermatozoon of Acesta oophaga (Bivalvia) is described by transmission electron microscopy. This cold-seep species produces ect-aquasperm, confirming that it is a broadcast spawner. The head of the sperm consists of a small, rounded, electron-dense nucleus, capped by a short conical acrosome, the contents of which are differentiated. The mid-piece contains a pair of orthogonally arranged centrioles surrounded by five spherical mitochondria. The gonad of one individual contained eggs and sperm, which supports the hypothesis that A. oophaga is a sequential hermaphrodite.

The recent Compendium of bivalves by Huber [(2010) Compendium of bivalves. ConchBooks, Hackenheim] introduces a large number of taxonomic and nomenclatural changes across the Bivalvia, worldwide. In this paper, we discuss a number of these changes that pertain to the New Zealand fauna. Although many of Huber's changes are justified, we find that there are a significant number with which we disagree, noting that many of them have been made in poorly understood groups with what seems to us rather weak evidence for the change. We have been guided by the belief that, in such cases, one should opt for taxonomic stability and await stronger data. We also argue that in a number of these difficult groups such data are likely to be molecular. We note also that in reviewing some of these cases, it has been convenient to make a small number of original changes. Recent records of Lima mestayerae Marwick, 1924 are based on mislocalised specimens of Lima nimbifer Iredale, 1924 from eastern Australia. Specimens from the...

Fourteen bivalve taxa belonging to 11 families are present in at least 13 early to middle Miocene hydrocarbon seep deposits in the East Coast Basin, North Island, New Zealand. Among these are at least three new species, one of which, Semeloidea (s. l.) bexhavenensis sp. nov. (Lasaeidae), is described here. New distribution data are recorded for bivalve species in the families Limidae, Propeamussiidae, Malleidae and Solemyidae. Additional morphological details of Gigantidas coseli (Mytilidae) and Pratulum quinarium (Cardiidae) are provided based upon previously unrecorded internal shell features. Palaeoecological analysis indicates that bivalves utilized a broad range of modes of life and niches within the New Zealand Miocene seep environment, and no more than ca. 30% of these bivalve species were likely to have been obligate to seeps.

Based on newly collected material from the uppermost Smithian and lower to middle Spathian (Oleneki- an, Lower Triassic) of the Salt Range and Surghar Range (Pakistan), 15 bivalve species belonging to 11 genera are described, including two new genera, Eobuchia and Dimor- phoconcha , and one new species, Palaeoneilo ? fortistriata . Eo- buchia gen. nov. is placed in a new subfamily, the Eobuchiinae, which differs from the Buchiinae in having an almost planar and only moderately inclined or offset right anterior auricle. Inclination of the right anterior auricle is proposed as a synapomorphy of the revised suborder Monotidina, which includes the Buchiidae, Monotidae, Oxytomidae and, tentatively, the Dolponellidae. The Pseudo- monotidae, Chaenocardiidae and Claraiidae are discussed as candidate ancestors of the Monotidina. Dimorphoconcha gen. nov., provisionally placed in the Limidae, is a morphologically unusual genus characterized by a globose shell centre and a strongly plicate fringe. Permophorus costatus , which was pre- viously known exclusively from Permian strata, is reported from the Spathian of the Surghar Range. This record extends the range of P. costatus for at least 8 Myr and makes it the first reported Lazarus species , with an outage of more than 2 Myr after the end-Permian mass extinction. Ten of 15 species recognized in this study have not been reported from other regions, which may indicate increasing provincialism towards the end of the Early Triassic, or, alternatively, reflect the still insufficient knowledge of ben- thic faunas from the epoch that followed the greatest crisis in the history of life.

Limatula chilensis sp. nov. is described on the basis of shell morphology and soft tissue anatomy. Studied individuals were obtained periodically between June 2008 and January 2009 from sublittoral soft-sediments off Punta Coloso in northern Chile at depths of 22 to 33 m. Shell morphology of the new species differs from the 4 described species of Limatula from the Pacific coast of South America and Antarctic Peninsula (5°-65°S). Main characteristics of L. chilensis include an average height of 3.50 mm (range 2.36-4.42, SD ± 0.60, n = 34), number of radial ribs 16-21 (mode = 20, SD= 1.69, n = 8) and greater shell obliqueness. L. chilensis is the only known species of the genus found off northern Chile.

Genetic connectivity and habitat characteristics were examined in two species of Acesta clams (Bivalvia: Limidae) from submarine seamounts and continental slopes along the western North America margin. Two species were identified from dive videos obtained with submarine remotely operated vehicles that surveyed a 2200-km range between 27� and 46� N latitude. Acesta sphoni was only found at shallower habitats (545‐860 m depth) in the southern part of this range, whereas Acesta mori was more abundant and widely distributed in deeper habitats (1029‐1996 m). Both species occurred on seamounts and on the walls of submarine canyons and continental slopes. Segregation of these species by depth exposes them to correlated differences in water temperatures and dissolved oxygen concentrations. Ninety-eight individuals sampled from seven seamounts and one escarpment locality were characterized with DNA-barcodes based on 643 base pairs of mitochondrial cytochrome-c-oxidase subunit I (COI). Further analysis of these sequences revealed no significant geographical subdivision across the sampled range. This lack of differentiation suggests ongoing genetic exchange between the seamount populations and those possibly distributed along the continental margins. Examination of regional bathymetric profiles suggested that an abundance of suitable habitat might exist along these margins.

A novel bacterium was discovered in the gills of the large bivalve Acesta excavata (Limidae) from coral reefs on the northeast Atlantic margin near the shelf break of the fishing ground Haltenbanken of Norway, and confirmed present in A. excavata from a rock-wall in the Trondheimsfjord. Purified gill DNA contained one dominant bacterial rRNA operon as indicated from analysis of broad range bacterial PCR amplicons in denaturant gradient gels, in clone libraries and by direct sequencing. The sequences originated from an unknown member of the order Oceanospirillales and its 16S rRNA gene fell within a clade of strictly marine invertebrate-associated Gammaproteobacteria. Visual inspection by fluorescent in situ hybridization and transmission electron microscopy indicated a pleomorphic bacterium with no visible cell wall, located in aggregates inside vacuoles scattered within the gill cells cytoplasm. Intracellular Oceanospirillales exist in bathymodiolin mussels (parasites), Osedax worms and whiteflies (symbionts). This bacterium apparently lives in a specific association with the Acesta.

Bivalve molluscs are known for shadow responses involving closure or retraction of the siphon and valve adduction. In representative genera [Spisula solidissima (Dillwyn, 1918), Mercenaria mercenaria (Linnaeus, 1758), Lima scabra (Born, 1778)], the pallial nerves contain photosensitive fibers that exhibit physiological shadow responses. These photoreceptors are inhibited by light but trigger an excitatory burst of spikes to a shadow, the off-response. Equivalent responses are seen in bivalve eyes, e.g., in optic fibers from the siphon tentacle eyes of Cardium edule (Linnaeus, 1758) and the mantle eyes of scallops (Pectinidae) and file clams (Limidae). In scallops, they form a distal retinal layer of ciliary receptors, distinct from a proximal microvillar layer that is excited by light. In off-receptors (ciliary), light inhibition is the result of a hyperpolarizing receptor potential with spikes generated on the rebound depolarization at dimming. In contrast, the proximal on-receptors are excited...

Five species of the genus Limatula and one of Limea were found in a total of 83 samples taken from deep waters (700– 1950 m) off Brazil. Limatula laminifera (Smith, 1885) and Limea lirata Allen, 2004 were not previously reported from Brazil. Limatula confusa (Smith, 1885) and L. louiseae Clarke, 1974, although already reported for Brazilian waters, have their distribution extended southward. Limatula domaneschii n.sp. is described from the Campos Basin (˜22° S). It is diagnosed by concentric lamellae strengthening towards the ventral margin of the shell, and absence of axial ornamentation; an internal median groove is not present. A fifth Limatula species is present, and we strongly suspect that it is also new to science, but a formal description is delayed until additional specimens are collected.

This paper describes 97 molluskan species (45 Bivalvia, 3 Scaphopoda, 49 Gastropoda) recovered from bathyal bottoms off Santa Maria di Leuca (Puglia, Italy), in the northern Ionian Sea, and provides data about their taxonomy, geographical distribution, habitat, ecological requirements and fossil record. Only 6 species remain unidentified, and all are illustrated. The bivalve-dominated assemblages belong to the so-called "cold-water coral ecosystem". They appear to depend mainly on substrate characteristics, with faunas related to hard substrate around coral-colonized mound tops, and mud-related ones in inter-mound areas, respectively. Nuculanoida and Pectinoidea among bivalves, and Conoidea and Pyramidelloidea among gastropods are the most diverse suprafamilial groups. The present paper is the first comprehensive taxonomic overview of Mediterranean bathyal mollusks including larval shell characters.

We have studied two congeneric limid bivalves, Acesta species novum and Acesta excavata (Bivalvia: Limidae), that live in similar physical conditions but use different food sources. Acesta sp. nov. live on the giant siboglinid tubeworm Lamellibrachia luymesi at cold seeps and feed on their eggs, a continuous food source that ultimately is derived from chemosynthesis, whereas A. excavata relies on planktonic food of photosynthetic origin, which varies seasonally. We hypothesized that these two species might show differences in the periodicity of reproduction; specifically, we predicted that A. sp. nov. would breed continuously and that A. excavata would demonstrate an annual reproductive cycle. Our hypothesis was refuted, as both species have a semi-continuous reproductive cycle. Food quality, quantity or seasonality had no clear effect. Reproductive adults are functionally gonochoristic. Females broadcast buoyant eggs with an average size of 179 μm in A. sp. nov. and 160 μm in A. excavata. Both the size of the larval shell and the size of the spawned eggs are suggestive of pelagic lecithotrophic development. Both species also appear to be protandric hermaphrodites, changing from male to female at approximately 77 and 90 mm shell height, respectively, although not all individuals change sex. In the material investigated in this study there was a biased sex ratio favouring males.

Here we report the first study of clearance rate and respiration rate of a deep living bivalve, Acesta excavata (J.C. Fabricius, 1779) (Mollusca: Limidae). We found that A. excavata had extreme values both for clearance and respiration rates compared to other bivalves. It has the second largest clearance rate ever reported, 13.36 l h − 1 g − 1 , and the second lowest value of respiration rate, 0.12 ml O 2 h − 1 g − 1 . The gill area of 7063 mm 2 g − 1 is one of the largest found in bivalves so far. We suggest that these values indicate a physiological adaptation to the low and irregular food supply in the deep sea rather that a specific adaptation to depth.

Knowledge about the marine malacofauna in the Magellan Region has been gained from many scientific expeditions that were carried out during the 19th century. However, despite the information that exists about molluscs in the Magellan Region, there is a lack of studies about assemblages of molluscs co-occurring with macroalgae, especially commercially exploitable algae such as Gigartina skottsbergii, a species that currently represents the largest portion of carrageenans within the Chilean industry. The objective of this study is to inform about the richness, systematics, and distribution of the species of molluscs associated with natural beds in the Strait of Magellan. A total of 120 samples from quadrates of 0.25 m2 were obtained by SCUBA diving at two sites within the Strait of Magellan. Sampling occurred seasonally between autumn 2010 and summer 2011: 15 quadrates were collected at each site and season. A total of 852 individuals, corresponding to 42 species of molluscs belonging to Polyplacophora (9 species), Gastropoda (24), and Bivalvia (9), were identified. The species richness recorded represents a value above the average richness of those reported in studies carried out in the last 40 years in sublittoral bottoms of the Strait of Magellan. The biogeographic affinity indicates that the majority of those species (38%) present an endemic Magellanic distribution, while the rest have a wide distribution in the Magellanic-Pacific, Magellanic-Atlantic, and Magellanic-Southern Ocean. The molluscs from the Magellan Region serve as study models for biogeographic relationships that can explain long-reaching patterns and are meaningful in evaluating possible ecosystemic changes generated by natural causes or related to human activities.

The previously unclear taxonomic status of the high-Antarctic bivalve Limatula ovalis Thiele, 1912 and the sub-Antarctic L. pygmaea (Philippi, 1845) was investigated using molecular techniques (18S rDNA, 16S rDNA, ITS-1). L. ovalis and L. pygmaea were recovered as sister taxa, and L. hodgsoni (Smith, 1907) as their sister, supporting the subgenus Antarctolima Habe, 1977. Various different molecular clock calculations placed the timing of the L. ovalis/pygmaea divergence (1.36–8.03 MYA with 16S rDNA, 6.81–19.12 MYA with 18S rDNA, 0.24–2.87 MYA with ITS-1) well after the formation of the Antarctic Polar Front (23.5 MYA, APF), indicating a more recent speciation process. The vicariance hypothesis that the APF is a barrier for geneflow favouring speciation processes in the Southern Ocean has to be questioned.

The cosmopolitan, Jurassic to Recent, bivalve Acesta (Limidae) is documented from Australian Cretaceous (upper Albian) rocks in the lowermost section of the Mackunda Formation of Queensland. These specimens from Landsborough Downs, Flinders Shire, represent an endemic new species, herein named Acesta (Acesta) backae n. sp. Acesta (A.) backae n. sp. was a shallow-water suspension feeder that inhabited the Cretaceous Australian epicontinental sea of the Great Artesian Basin. Although hinge details of Acesta (A.) backae n. sp. are wanting, this new taxon is most closely allied with Acesta? sp. of the Miria Formation of Western Australia and can clearly be discriminated from other Cretaceous Austral forms.

Two species of limid clams, Acesta sphoni and Acesta mori, were observed and sampled from seven localities in the Gulf of California, Mexico. The two species are known to occur on seamounts and escarpments along the north-eastern Pacific margin of the United States. This report provides the first records of each species in the Gulf of California and the greatest depth records for both species. Though they occasionally overlap geographically, the two species are clearly stratified by depth, with A. sphoni occupying shallower and warmer, hypoxic waters, and A. mori occupying deeper and colder, oxic waters. The species are easily distinguished morphologically. The shells of A. mori have very fine radial ribbing for a smooth appearance and are more rounded and inflated, whereas those of A. sphoni are narrower and more elongate with 31 to 77 strong radial ribs. The largest individuals sampled were A. sphoni. For each species, DNA analyses revealed arrays of mitochondrial haplotypes similar to those found previously at north-eastern Pacific localities along the California, Oregon and Washington margins, providing no evidence for geographical subdivision throughout this newly extended range.

Background During the TALUD XV research cruise off the southern part of the Baja California Peninsula, Mexico, samples of macro-invertebrates obtained in the deep-sea (296–2136 m) revealed a rich fauna of bivalves (17 species belonging to 10 families). The number of species per station varied from one to five. The richest families were Nuculidae, Nuculanidae, Neilonellidae, Limidae, and Cuspidariidae. Solemyidae, Lucinidae, Poromyidae, Verticordiidae, and Pectinidae were each represented by a single species. Some species groups need a thorough revision and were tentatively identified (Nuculana cf. hamata, Limatula cf. saturna). New information Significant new distribution information is provided for two species, both recorded for the first time from off western Mexico: Ennucula panamina with an extension of its known distribution over 20° of latitude north and Jupiteria callimene with an extension of 16° 42' of latitude to the north. One species (Ennucula taeniolata) is reported in shallower depth and one in deeper water (Acesta sphoni). New records are provided for an additional nine species. Environmental and habitat conditions are given for the first time for many of the bivalve species.

Nuculid bivalves of the Cape Melville Formation (Early Miocene, King George Island) are reviewed. Ten bivalve taxa are listed from the formation in the families Nuculidae (two species), Sareptidae, Malletiidae, Limopsidae (two species), Limidae, Pectinidae, Hiatellidae, and Periplomatidae. The Nuculidae consist of two species of Leionucula Quenstedt, 1930. One of these, L. melvilleana n. sp., is described and the other consists of the two species named previously by Anelli et al. (2006), which are demonstrated to be synonymous and are assigned to the species Leionucula frigida (Anelli, Rocha-Campos, Santos, Perinotto & Quaglio 2006). This assemblage, dominated by protobranchs (89% of specimens), is a typical fauna of offshore soft substrates, with a few specimens transported from hard substrates nearby. The diversity of Nuculidae has decreased in the Antarctic region through the Cenozoic.

During identification of bivalve molluscs collected in Antarctica, a rich taxonomic bibliography was gathered, stimulating comparisons with the Brazilian malacofauna. We listed a total of 68 and 368 known shallow-water species (less than 200 m depth) from Antarctica and Brazil, respectively, in order to find species, families and superfamilies in common, and to investigate how these malacofaunas differ in regard to these representative groups and their life habits. There are 23 superfamilies absent in Antarctica, but present in Brazil with at least one species; the reverse does not occur, as all superfamilies known from Antarctica are also recorded from Brazil. The number of Brazilian species is higher, being composed of a mixture of taxa from different biogeographical provinces, whereas in Antarctica there are only a few species adapted to its polar conditions, with minor components from elsewhere. Thus, many typical Caribbean species extend into Brazil, belonging to the diverse Arcoidea, Pectinoidea, Lucinoidea, Cardioidea, Veneroidea, and Tellinoidea. Cemented Ostreoidea, Plicatuloidea, Dimyoidea, Spondylidae (Pectinoidea), and Chamoidea are absent from Antarctica, as are wood (Teredinidae, Pholadoidea) and rock borers (Pholadidae, Pholadoidea; Gastrochaenoidea; and Lithophaginae, Mytiloidea). A large number of Brazilian species of infaunal (e.g., Tellinidae, Veneridae, Cardiidae, and Mactroidea) and epifaunal groups (Pectinidae, Mytilidae, and Arcidae) are absent from or poorly represented in Antarctica. Nuculanoidea, Limopsoidea, Lucinoidea, Galeommatoidea, Cyamioidea, and Cuspidarioidea are the richest groups in Antarctica; some of them are also represented by several species in Brazil, albeit in deeper waters. Three species are recorded as living in both places: Limatula pygmaea (Limidae), Lasaea adansoni (Lasaeidae), and Gaimardia trapesina (Gaimardiidae). Through the analysis of these groups from each fauna, it is possible to identify those that are taxonomically diverse in one place or another, and then emphasize them in ecological studies, eventually using them as model or monitoring organisms. The present paper can be a starting point for future discussion on the existing latitudinal gradients along the coast of eastern South America, stimulating studies on changes occurring in the composition of the faunas of bivalves from Brazil, Uruguay, Argentina, and Antarctica. Durante a identificação de moluscos bivalves coletados na Antártica, foi reunida uma rica bibliografia taxonômica, estimulando comparações com a malacofauna do Brasil. Assim, listamos um total de 68 espécies conhecidas para águas rasas (menos de 200 m de profundidade) da Antártica e 368 para o Brasil, procurando encontrar espécies, famílias e superfamílias em comum a ambos os locais, e investigando em que essas malacofaunas diferem em relação aos grupos representados e em relação ao hábito de vida das suas espécies. Vinte e três superfamílias não possuem representantes antárticos, mas estão presentes com pelo menos uma espécie brasileira; o oposto não ocorre, pois todas superfamílias que ocorrem na Antártica também são conhecidas para o Brasil. O número de espécies brasileiras é maior, composto por uma mistura de táxons de diferentes províncias biogeográficas, enquanto na Antártica existem somente poucas espécies adaptadas às condições polares, com uma minoria de representantes de fora da Antártica. Dessa forma, muitas espécies típicas do caribe se distribuem até o Brasil, pertencendo aos diversos Arcoidea, Pectinoidea, Lucinoidea, Cardioidea, Veneroidea e Tellinoidea. Cimentantes Ostreoidea, Plicatuloidea, Dimyoidea, Spondylidae (Pectinoidea) e Chamoidea não estão presentes na Antártica, como também não estão perfuradores de madeira (Teredinidae, Pholadoidea) e de rochas (Pholadidae, Pholadoidea; Gastrochaenoidea; e Lithophaginae, Mytiloidea). É notável o grande número de espécies brasileiras de grupos infaunais (exemplos, Tellinidae, Veneridae, Cardiidae e Mactroidea) e epifaunais (Pectinidae, Mytilidae e Arcidae), que são ausentes ou pobremente representados na Antártica. Nuculanoidea, Limopsoidea, Lucinoidea, Galeommatoidea, Cyamioidea e Cuspidarioidea são os grupos mais ricos em espécies antárticas, alguns deles também sendo especiosos no Brasil, entretanto, em maiores profundidades. Três espécies são registradas para ambos os locais: Limatula pygmaea (Limidae), Lasaea adansoni (Lasaeidae) e Gaimardia trapesina (Gaimardiidae). Através de análises dos grupos, é possível apontar aqueles que são taxonomicamente diversos em uma ou outra fauna, e então enfatizá-los em estudos ecológicos, utilizando-os como "organismos monitores" ou modelos. O presente trabalho pode ser um ponto de partida para futuras discussões sobre a ocorrência de um gradiente latitudinal ao longo da costa leste da América do Sul, estimulando trabalhos sobre mudanças que ocorrem na composição das faunas de bivalves do Brasil, Uruguai, Argentina e Antártica.

The option of storing CO2 in subsea rock formations to mitigate future increases in atmospheric CO2 may induce problems for animals in the deep sea. In the present study the deep-sea bivalve Acesta excavata was subjected to environmental hypercapnia (pHSW 6.35, P CO 2 = 33,000 μatm) corresponding to conditions reported from natural CO2 seeps. Effects on acid–base status and metabolic rate were related to time of exposure and subsequent recovery. During exposure there was an uncompensated drop in both hemolymph and intracellular pH. Intracellular pH returned to control values, while extracellular pH remained significantly lower during recovery. Intracellular non-bicarbonate buffering capacity of the posterior adductor muscle of hypercapnic animals was significantly lower than control values, but this was not the case for the remaining tissues analyzed. Oxygen consumption initially dropped by 60%, but then increased during the final stages of exposure, which may suggest a higher tolerance to hypercapnia than expected for a deep-living species.

Neoinoceramus Ihering, 1902, hitherto placed in the family Pernidae, is shown to be a member of the family Limidae, according to its edentulous hinge, well-defined ligamentary pit, and biauriculated shell. It was an epibenthonic bivalve living attached by a byssus to the hard substrate in a platform environment where some epibionts (muricaceous gastropods, sponges) were fixed on its shell.

We analyze the morphological and genetic variability within and between seven species of Acesta and specimens recently collected in the northwest Atlantic using traditional morphological measurements, landmark-based geometric morphometrics, and the cytochrome oxidase subunit I (COI) gene sequences, with particular emphasis on North Atlantic species. Shell morphology and external shell appearance do not allow reliable distinction between the widely recognized northeastern Atlantic A. excavata and other northwest Atlantic species or populations of Acesta, with the exception of A. oophaga. Similarly, shape analysis reveals a wide variability within northeastern Atlantic A. excavata, and significant morphological overlap with A. bullisi from the Gulf of Mexico and A. rathbuni from the southwestern Pacific and South China Sea. Specimens from the northwestern and Mid-Atlantic display shell shapes marginally similar to that of A. excavata. These differences are at least partly related to anterior or posterior shifting of the shell body and to the opposite shifting of the hinge line/dorsal region and upper lunule. These morphological variations, along with the midline-width-ratio, explain much of the variability extracted by principal component analysis. Results from a mitochondrial DNA barcode approach (COI), however, suggest that the northwest Atlantic specimens belong to a new species for which we propose the name Acesta cryptadelphe sp. nov. Differences in larval shell sizes between northeastern and northwestern Atlantic specimens are consistent with this result.

(Bivalvia; Limidae), that has evolved special-ized mechanisms to exploit a unique source of nutritionderived ultimately from chemosynthesis: the energy-richeggs of giant tubeworms. Opportunistic egg or embryopredators are common among terrestrial vertebrates (2, 3)and marine invertebrates (4). Egg specialists are found insome groups of insects, including ichneumonid wasps (5)and phorid flies (6) and at least one genus of nemertean (7),but we know of no marine animals other than

Acesta excavata is the largest known bivalve associated with the Lophelia pertusa communities along the northeast Atlantic continental margin, but has also been found along steep cliffs, devoid of bathyal corals, and on more subdued topographies. During the Pleistocene, including the last glacial, A. excavata was widespread in the Mediterranean, but is in the Recent fauna known only from four Mediterranean sites. A new possible live-record from the Canyon du Var off Nice is presented. Radiocarbon dating (AMS 14C-method) on an A. excavata assemblage from the Strait of Sicily yielded a Late Pleistocene age of 39.9 ka. Biometric parameters indicate that Pleistocene Mediterranean shells achieved about the same maximum sizes as their Recent Atlantic counterparts, but individuals have been slightly smaller on average. The subspecies Acesta excavata sublaevis Nordsieck, based on a subfossil juvenile Mediterranean shell, is not considered a valid taxon. Mineralogical composition and ultrastructure of A. excavata have been analyzed using thin-sections, Feigel staining, x-ray diffractometry (XRD) and SEM-imaging. Its wide distribution, large size (15 cm) and simple shell architecture makes it a prime candidate for palaeoenvironmental studies in cold-water coral settings.

Two large bivalve specimens collected in Bay d’Espoir, a deep fjord situated on the south coast of Newfoundland, are described and identified as belonging to the species Acesta excavata (Fabricius 1779). In situ observations onboard the manned submersible PISCES IV and color videos have provided information on the vertical distribution, density and habitat of the species. Maximum abundances of about 15 large individuals/m2 occurred on sheltered rock outcrops at depth ranging from 550 to 775 m, where warm (6°C) continental slope water is found. Differences in shape and thickness between the valves of the two specimens appear to be related to the degree of exposure to rock falls (i.e., sheltered versus exposed habitat). Prior to this account, the European Giant File Clam had never been encountered west of the Azores Islands in the North Atlantic.

Marine file clams of family Limidae d'Orbigny, 1846 (+ Radulidae Adams & Adams), characterised by their often colourful mantle and pallial tentacles and by swimming behaviour, are commonly collected and illustrated bivalves. Based on new material from an extensive Florida Keys biodiversity survey plus museum and literature data, western Atlantic species of Lima Bruguière, 1797 (+ Mantellum R�ding; Radula M�rch; Limaria Rafinesque; Austrolima Iredale; Meotolima Oyama) and Ctenoides M�rch, 1853 (+ Divaricolima Rovereto) are revised. Lima includes L. marioni Fischer, 1882 (+ L. lata Smith; lectotype selected), and L. caribaea d'Orbigny, 1842 (lectotype selected), distinguished from eastern Atlantic L. lima (Linné) and other species by shell rib number. Ctenoides includes C. scaber (Born, 1778) (+ Ostrea glacialis Gmelin; L. asperula Lamarck; Limaria asperula Link), C. mitis (Lamarck, 1807) (+ L. tenera Sowerby; L. floridana Olsson & Harbison), C. planulatus (Dall, 1886) (lectotype selected), C. sanctipauli Stuardo, 1982, and C. miamiensis, C. obliquus, and C. vokesi, spp. nov. Species distinctions rely mainly on shell characters, although body colour and ornamentation are confirming in some cases. Diagnostic shell characters at the genus-level are supported by new anatomical characters of the gut and tentacles. Known anatomical data for worldwide Lima and Ctenoides species are summarised within a phylogenetic context.

Oxygen consumption rates (\(\dot V_{{\text{O}}_2 } \)) and a number of possible anaerobic end products were determined forLimaria fragilis at rest, and following active swimming.

The proposal by Atkins (1938), that the Bivalvia can, on the basis of the composition of the latero-frontal ciliated tracts, be divided into two groups, the Macrociliobranchia and the Microciliobranchia, is examined. It is concluded that the Ostreidae, in which the latero-frontal tracts consist of compound cirri together with subsidiary simple cilia, should not be grouped with the Microciliobranchia. The remaining families in this group are characterized by the possession of latero-frontal tracts consisting of simple cilia only; the Pinnidae show some modifications of the latero-frontal tracts, the precise details of which are still to be determined. The form of the gill in the Anomiidae, Pectinidae, Limidae and Pinnidae is reviewed. It is suggested that in these families, possibly correlated with latero-frontal tracts consisting of simple cilia only, the collection and transport of particles by the gill for possible ingestion is primarily dependent upon the flow of water currents rather than direct ciliary action as in those bivalves which possess compound eu-latero-frontal cirri. The families possessing latero-frontal tracts consisting of simple cilia only are all included in the subclass Pteriomorphia, together with two families, the Mytilidae and Ostreidae, which possess compound latero-frontal cirri. Some workers already exclude the Mytilidae from the Pteriomorphia. It is suggested that before discounting the value of the laterofrontal tracts in indicating relations there should be a reappraisal of the position of the Ostreidae.

A study of three bivalves of the genera Lima and Limaria has demonstrated that two evolutionary processes are at work within the Limidae; both are of major significance. The first process concerns a reduction in the importance of the shell as a means of protection and the assumption of such responsibility by the middle mantle fold possessing autotomising tentacles. The tentacles also aid swimming by undertaking a rowing action and the thin shell aids swimming by reducing the sinking rate. A second major evolutionary trend which facilitates swimming concerns the gradual changeover from a ciliary to a muscular based means of expelling pseudofaeces both posteriorly (as in the typical bivalve) and via a subsidiary anteriorly directed aperture; in less specialised limids this rejection tract is located ventrally. The anterior exhalant current has also profoundly affected the structure of the lip apparatus. To prevent food material from being flushed out of the oral grooves by this stream the lips have become fused over the mouth. Successive stages in a process of lip fusion have been recognised and correlated with the evolution of the anteriorly directed rejection tract, the full importance of which, both in terms of mobility and morphological specialisation, is now better understood. A new limid, Limaria (Platilimaria) hongkongensis, from Hong Kong is described.

About 150 named fossil and living species of Limidae grouped in the genus Limatula Searles Wood are listed. They range from Jurassic (perhaps Triassic) to Recent and are now distributed in all oceans and seas from the Arctic to the Antarctic. The genus has not previously been subdivided, but its phylogenetic and biogeographic history can only be approached by recognizing a number of species-groups, some of which are formally proposed as subgenera, using characters of shell shape and ornament that appear to be conservative. Four subgenera are recognized (two new) for 40 living and fossil species-group taxa from Australia and adjacent parts of the Pacific and Southern Ocean: Limatula s. str. (with several groups), Limatuletta nov. (type: L. japonica Adams), Stabilima Iredale (3 species groups) and Squamilima nov. (type: Lima hodgsoni E. A. Smith). The following new species and subspecies are proposed: L. trulla arcis (Oligocene, New Zealand and Victoria), L. powelli (Recent, New Zealand, New South Wales and...

SynopsisThe Mollusca possess two growth axes associated with the body and the mantle/shell respectively. Evolution of the Lamellibranchia involved assumption by the mantle/shell of responsibility for growth and form; also the formation of anterior and posterior adductors. Change from this dimyarian to a heteromyarian and finally monomyarian condition involved changes in the relations of body and mantle/shell. These are considered with regard to their two major axes in the saggital plane. Although body form may be greatly influenced by changes in that of the mantle/shell, its proportions are only altered where the body is attached by byssus. Then the anterior half may be reduced and the anterior adductor finally lost. This occurs in many Anisomyaria, these monomyarians being divisible into five groups according to habit. Apart from the Limidæ, all are bilaterally asymmetrical. In those which have lost the foot, both axes of the body are effectively lost. Primary pallial attachment is lost but secondary attachment has been achieved in most cases. In the Tridacnidæ (Eulamellibranchia) the mantle/shell has rotated in the saggital plane in relation to the fixed body with resultant loss of the anterior adductor. There is hypertrophy and extension antero-dorsally of the originally posterior siphonal tissues in which zooxanthellæ are contained. Evolution may have proceeded by way of now extinct heteromyarians such asLithocardium. In the freshwaterAcostœa(Mulleria) the anterior adductor is lost during growth following cementation by one or other valve. The form of the body is little affected. Variation and natural selection account for the variety of form and habit exhibited by these diverse monomyarians.

Summary. 1 The internal structure and the ciliary sorting mechanisms of the stomach are described for representatives of twelve families of Filibranchia and Pseudolamellibranchia. 2 The variable structural features of the stomach are examined individually, and it is shown that only one of these is suitable for use as a diagnostic in assigning the stomachs of these lamellibranchs to a limited number of types. This feature is the form of the major typhlosole. 3 The major typhlosole may sweep smoothly from the orifice of the mid-gut to that of the left pouch, accompanied on its course by the ciliated rejection tract of the intestinal groove. Alternatively a long slender tongue may pass forwards from the major typhlosole and penetrate deeply into the food-sorting caecum, this tongue being accompanied by a similar extension of the intestinal groove. No intermediate condition was found, and on this basis the stomachs in eight families were assigned to Type III, in which the major typhlosole possesses such a tongue. These families are the Arcidae, Glycimeridae, Limopsidae, Pinnidae, Vulsellidae, Pteriidae, Mytilidae and Ostreidae. 4 It is considered that the evolution of a tongue of the major typhlosole, extending into the food-sorting caecum, could not have occurred independently on two or more occasions, nor is it likely that such a tongue, once having been formed, could have been lost independently on two or more occasions. It is concluded, therefore, that the above mentioned eight families constitute the end products of one phylogeny of lamellibranchs. 5 In the remaining four families, the Trigoniidae, Limidae, Pectinidae and Anomiidae, the major typhlosole lacks a tongue. The stomachs in these four families are assigned to Type IV, and attention is drawn to the fact that in many Eulamellibranch families the internal structure of the stomach is similar. 6 It is suggested that evolution of the structure and function of the interior of the stomach has played an important part in the adaptive radiation of the Lamellibranchia. 7 It is reiterated that the Protobranchia constitute a phylogeny which is distinct from all other lamellibranchia and that it is undesirable to link the Protobranchia with the Arcacea to form the order Taxodonta.

Examination of the labial structures of 36 species in 24 genera of the Anisomyaria demonstrates that true hypertrophy occurs only in the Pectinidae s.1., Spondylidae, and Limidae. The Propeamussidae lack enlarged lips, evidence supporting their removal from the Pectinidae. Observation of living materials has suggested that rather than serving as a food-retentive hood, the enlarged lips perform a screening function.

Certain Lamellibranchs have the latero-frontal tract composed of large complex ‘cilia’, here called eu-latero-frontal cilia , together with subsidiary ones, termed pro-latero-frontal cilia. This type of latero-frontal tract occurs in some or all of the three families of Protobranchs (there is some doubt as to the presence of pro-latero-frontal cilia in all the families), and in the Mytilidae and probably the Trigoniidae (fixation too imperfect for the identification of pro-latero-frontal cilia) among the Filibranchs, and in all the marine families of Eulamellibranchs obtainable at Plymouth, and in the fresh-water families, Dreissensiidae, Sphaeriidae, Unionidae, Mutelidae, and Aetheriidae. A list of the species investigated is given. Other Lamellibranchs, which were previously considered as lacking latero-frontal cilia, have been found to possess small ones only, difficult of observation, termed micro-latero-frontal cilia. These occur in the Arcidae, Anomiidae, Pteriidae, Pectinidae, Spondylidae, Limidae, Pinnidae, and are inferred to be present in the Amussiidae, Vulsellidae, and Isognomonidae, in which eu-latero-frontal cilia are certainly absent. A list of the species examined is given. In one family, the Ostreidae, moderate-sized latero-frontal cilia, termed anomalous latero-frontal cilia, together with subsidiary ones, termed para-latero-frontal cilia are present. In bivalves having eu-latero-frontal cilia the arrangement of the various ciliary tracts, frontal, latero-frontal, and lateral is fairly constant, notable exceptions being a Protobraneh, Nuculana, and a Filibranch, Trigonia . In bivalves having micro-latero-frontal cilia the arrangement of the various tracts seems more or less constant. The homology of the various types of latero-frontal cilia is discussed. The composition of the latero-frontal ciliated tracts has been found to be a stable character, and, as it is correlated with other characters, has taxonomic value. It is suggested that the variations in the constitution of the latero-frontal tracts tend to show that Ridewood's (1903) classification does not express genetic affinities, as he himself conceded, nor does Pelseneer's (1911) entirely, and that Pelseneer's order Filibranchia, and Ridewood's orders Bleutherorhabda and Synaptorhabda are not monophyletic. Families possessing micro-latero-frontal cilia appear to be closely related, and form a group, which, with certain modifications, corresponds to ‘the Aviculidae and their allies’, or the ‘sedentary’ branch of Lamellibranchs, previously established by the palaeontologists, Jackson and Douvillé respectively, largely on shell characters. Thus the constitution of the laterofrontal tracts of the gill filaments supports the findings of palaeontologists with regard to this group. Unfortunately neither Jackson nor Douville proposed a formal name for the group. The relationship of forms with micro-latero-frontal cilia, and the evolution within the group of the eulamellibranchiate or synaptorhabdic gill are discussed. One family, the Ostreidae, which must be included on account of its relationship with either the Pteriacea or Pectinacea (based on other evidence) has moderatesized, or anomalous latero-frontal cilia together with paralatero-frontal cilia. The anomalous latero-frontal cilia differ in certain respects from the large cilia characteristic of the majority of the Laraellibranchia, and are presumed to have arisen independently. Common characters of the group characterized by the possession of micro-latero-frontal cilia, in addition to the form of the latero-frontal cilia, are: (1) shell characters of the prodissoconch, Arcidae excepted; (2) byssal fixation; (3) considerable free posterior region to the gill axes; (4) considerable development of muscles in the gill axes, Ostreidae excepted; (5) method of division of the pallial cavity, Ostreidae excepted; (6) gills without a supra-axial extension to the outer demibranch; (7) presence of longitudinal currents at the free ventral edge of both inner and outer demibranchs; and of opposed frontal currents on all lamellae and frequently on the same filament, Pinnidae excepted; (8) absence of pallial sutures, Pinnidae and Ostreidae excepted; (9) inner fold of the mantle margin characteristically well developed, especially in swimming forms; (10) insertion of the retractor muscles of the mantle margin at a considerable distance from the shell edge, Arcidae excepted; (11) tendency for members, except the Ostreidae, to lie on the right valve; (12) abdominal sense organs on the posterior adductor muscle; and (13) intercommunication of the auricles, Anomiidae excepted. Two groups of the Lamellibranchia are proposed provisionally, namely Group I, Macrociliobranchia, including the orders Protobranchia (Pelseneer), Filibranchia (emended to include only the Mytilacea and Trigoniacea), Eulamellibranchia (Pelseneer, 1911), and Septibranchia (Pelseneer); and Group II, Microciliobranchia, with the order Pseudolamellibranchia, emended to include the sub-orders Arcacea (excluding the Trigoniidae), Anomiacea, Pteriacea, Pectinacea, and Ostreacea. The Macrociliobranchia will need revision, for it is very probable that the Filibranchia (emended), if not the Eulamellibranchia, are still not monophyletic.

We examined the reproductive cycle of a tropical bivalve, the fire scallop Lima (Ctenoides) scabra (Born, 1778), over a 14 months period in the Golfo de Cariaco, Venezuela, and the association of gonadal growth and spawning with environmental factors. Most small individuals were males and most large individuals females, indicating the protandrous characteristic of this species. We documented three marked decreases in gonadal mass, from late October to December 1992, from early June to early July 1993 and from late October to early December 1993, and all were associated with drops in temperature related to renewed upwelling. This suggested that major synchronized spawnings were stimulated by drops in temperature or other factors related to the onset of upwelling. Multiple regression analyses indicated that the major environmental factor associated with increases in gonadal mass was phytoplanktonic food availability. Analyses of regressions of mass of somatic tissues to shell height suggested decreases in reserves in somatic tissues at the end of the November-December spawnings, but not at the end of the June-July spawning. This may be because body reserves are used for reproduction during November and December when phytoplanktonic food availability is low.

The file shell L. fragilis displays a slow sustained style of swimming indicative of basically aerobic mechanisms of ATP production. Although it had been proposed that anaerobic glycolysis and arginine phosphate did not contribute to powering swimming, the discovery of high activity of arginine kinase and significant activities of strombine and alanopine dehydrogenases in the adductor muscle led to a reexamination of the relative contributions of aerobic metabolism, anaerobic glycolysis and arginine phosphate during swimming. It was found that, whereas aerobic metabolism predominates with only a minor contribution from anaerobic glycolysis, arginine phosphate supplied up to 23% of the ATP used during 5 min of sustained swimming.