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To broaden the anatomical knowledge of marine bivalves, detailed gross anatomical studies of 20 species from the Florida Keys are presented, representing 19 families: Solemya occidentalis Deshayes, 1857 (Solemyidae), Propeleda carpenteri (Dall, 1881) (Nuculanidae), Arcopsis adamsi (Dall, 1886) (Noetiidae), Limopsis aff. cristata Jeffreys, 1876 (Limopsidae), Brachidontes exustus (Linnaeus, 1758) (Mytilidae), Isognomon alatus (Gmelin, 1791) (Isognomonidae), Hyotissa mcgintyi (Harry, 1985) and H. hyotis (Linnaeus, 1758) (Gryphaeidae), Pinna carnea Gmelin, 1791 (Pinnidae), Spondylus americanus Hermann, 1781 (Spondylidae), Plicatula gibbosa Lamarck, 1801 (Plicatulidae), Anomia simplex d'Orbigny, 1853 (Anomiidae), Carditamera floridana Conrad, 1838 (Carditidae), Entodesma beana (d'Orbigny, 1853) (Lyonsiidae), Codakia orbicularis (Linnaeus, 1758) (Lucinidae), Chama macerophylla Gmelin, 1791 (Chamidae), Lamychaena hians (Gmelin, 1791) (Gastrochaenidae), Polymesoda floridana (Conrad, 1846) (Cyrenidae), La...

We present the first DNA taxonomy publication on abyssal Mollusca from the Clarion-Clipperton Zone (CCZ), central Pacific ocean, using material collected as part of the Abyssal Baseline (ABYSSLINE) environmental survey cruise 'AB01' to the UK Seabed Resources Ltd (UKSRL) polymetallic-nodule exploration area 'UK-1' in the eastern CCZ. This is the third paper in a series to provide regional taxonomic data for a region that is undergoing intense deep-sea mineral exploration for high-grade polymetallic nodules. Taxonomic data are presented for 21 species from 42 records identified by a combination of morphological and genetic data, including molecular phylogenetic analyses. These included 3 heterodont bivalves, 5 protobranch bivalves, 4 pteriomorph bivalves, 1 caudofoveate, 1 monoplacophoran, 1 polyplacophoran, 4 scaphopods and 2 solenogastres. Gastropoda were recovered but will be the subject of a future study. Seven taxa matched published morphological descriptions for species with deep Pacific type localities, and our sequences provide the first genetic data for these taxa. One taxon morphologically matched a known cosmopolitan species but with a type locality in a different ocean basin and was assigned the open nomenclature 'cf' as a precautionary approach in taxon assignments to avoid over-estimating species ranges. One taxon is here described as a new species, Ledella knudseni sp. n. For the remaining 12 taxa, we have determined them to be potentially new species, for which we make the raw data, imagery and vouchers available for future taxonomic study. The Clarion-Clipperton Zone is a region undergoing intense exploration for potential deep-sea mineral extraction. We present these data to facilitate future taxonomic and environmental impact study by making both data and voucher materials available through curated and accessible biological collections.

The bivalve Limopsis cristata pursues a semi-endobenthic life in abyssal soft sediments. It attaches to particles by up to three byssal threads and filter feeds by inhaling water from posterior and anterior directions. Because of partial burial, however, only the latter is functionally significant. Complex ciliary currents in the mantle cavity concerned with the rejection of unwanted particles keep most material out of the simplified intestine. It is generally considered that the ligament is the constraining force in arcoid evolution. This may be true in part, but the lack of pallial fusions and the retention of anterior and posterior inhalant flows are more powerful limits to radiation in the Arcoida. In the deep sea, the Limopsidae has radiated into many micro-niches through micro-morphological adaptations. Loss of the arcoid ‘heel’ has resulted in the union of the separate rejectory currents of the visceral mass and foot, creating a single discharge point in more advanced bivalves. This greatly simplifies the rejectory roles of the visceral mass and foot and is thus of functional and selective advantage.

Early ontogenetic shells of Limopsis angusta, L. aurita, L. cristata, L. friedbergi and L. minuta are described in detail and their morphogenetic traits discussed in a phylogenetic context. Prodissoconch length is found to range from 170–370 µm discounting the so-called prodissoconch 2 stage of authors. Reports of such a stage refer to the early postlarval ‘interdissoconch’. Prodissoconch sizes are indicative of lecithotrophy but not of brooding. Limopsid-like prodissoconchs are rather common among pteriomorphs and at present of little use for phylogenetic interpretations, therefore. The early postlarval hinge is characterized by two tooth generations: an early one, (G1), representing the postlarval continuation of provincular teeth, and a late one, (G2), representing the independent adult dentition. This is a plesiomorphic trait for Pteriomorphia. The postlarval ligament is continuous with the larval resilium; it is neither co-functional with nor is it substituted by the typical duplivincular li...

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.

Seven species of marine bivalves, including six new taxa, are described from the Cape early Miocene Melville Formation which crops out on the Melville Peninsula, King George Island, West Antarctica. The bivalve assemblage includes representatives of the families Nuculidae, Ennucula frigida sp. nov., E. musculosa sp. nov.; Malletidae, Neilo (Neilo) rongelii sp. nov.; Sareptidae, Yoldia peninsularis sp. nov.; Limopsidae, Limopsis psimolis sp. nov.; Hiatellidae, Panopea (Panopea) sp. cf. P. regularis; and Pholadomyoida (Periploma acuta sp. nov.). Species studied come from four sedimentary sections measured in the upper part of the unit. Detailed morphologic features of nucloid and arcoid species are exceptionally well preserved and allow for the first time reconstruction of muscle insertions as well as dentition patterns of Cenozoic taxa. Known geological distribution of the species is in agreement with the early Miocene age assigned to the Cape Melville Formation. The bivalve fauna from Cape Melville Format...

The functional and adaptive morphology of six species of the genus Limopsis from deep water of the Atlantic is investigated and the following species and subspecies are described: L. aurita, L. surinamensis (new species), L. tenella, L. minuta, L. cristata cristata, L. cristata affinis, L. cristata intermedia (new subspeices), L. cristata lanceolata (new subspecies), L. galathea . Species of the genus Limopsis are among the relatively few suspension-feeding bivalves of the deep sea. The genus is not represented in shelf faunas. It is byssate, but the species described here show a change in habit from the exobyssate to the endobyssate condition and a corresponding reduction in the number and coarseness of the byssus threads produced. While the morphology of the species is similar in all the species described, differences being restricted to minor variation in the gills and palps, the viscera are confined to a small dorsal portion of the mantle cavity. Thus, while small body size is related to the paucity of food, production of a large thick shell may require a relatively small proportion of the energy input and yet confer advantage possibly in protection and in feeding mechanism. Eggs are relatively few and of a size indicating that the larvae are planktonic but non-feeding. The widely occurring species L. tenella shows differences in the shell characters of different populations. In L. cristata variation is such that it has been possible to describe subspecies.

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 structure of species ofNucula,Leda,YoldiaandSolenomyaled Pelseneer (1891), in his classic work on the morphology of the Lamellibranchia, to establish for their inclusion the order Protobranchia. He regarded them as in almost all respects a primitive group, and Stempell (1898 a, 1898 b, 1899) came to very similar conclusions. Later (1898, 1911) Pelseneer extended his work on these animals, grouping all recent species in the three families Solenomyidae, Nuculidae and Ledidae ( = Nuculanidae). On the other hand, Neumayr (1891), on the basis of the hinge characters, grouped all but the first of these families with the Arcidae, Glycymeridae and Limopsidae in the order Taxodonta. Thiele (1934) elaborated this classification, dividing the Taxodonta into two divisions, Nuculacea and Arcacea, and subdividing the former into the four families Nuculidae, M alletiidae, Ledidae ( = Nuculanidae) and Solenomyidae. Finally, Douville (1912), in his illuminating sketch of a possible classification of the Lamellibranchia, regarded the Nuculidae and the Nuculanidae as affording some indication of the original characters of those Lamellibranchia which took to a more or less active life on the sea bottom, and the Solenomyidae as representing to some extent ancestral conditions to those which assumed life in burrows. Douville’s views have been well summarized by Davies (1933, I935).* Verrill and Bush (1897, 1898) have given the best account of the shell characters of the Protobranchia, while knowledge of m any aspects of their morphology has recently been extended by Heath (1937).