BackgroundDespite extensive knowledge on bivalve anatomy and development, the formation and differentiation of the mantle margin and its associated organs remain largely unclear. Bivalves from the family Pectinidae (scallops) are particularly promising to cast some light on these issues, because they exhibit a complex mantle margin and their developmental stages are easily obtained from scallop farms. We investigated the mantle margin of the scallop Nodipecten nodosus (L. 1758) during larval and postmetamorphic development.MethodsA thorough analysis of the mantle margin development in Nodipecten nodosus, from veliger larvae to mature adults, was conducted by means of integrative microscopy techniques, i.e., light, electron, and confocal microscopy.ResultsInitially unfolded, the pallial margin is divided into distal and proximal regions by the periostracum-forming zone. The emergence of the pallial musculature and its neural innervation are crucial steps during bivalve larval development. By the late pediveliger stage, the margin becomes folded, resulting in a bilobed condition (i.e., outer and inner folds), a periostracal groove, and the development of different types of cilia. After metamorphosis, a second outgrowth process is responsible for emergence of the middle mantle fold from the outer surface of the inner fold. Once the three-folded condition is established, the general adult features are rapidly formed.ConclusionsOur data show that the middle mantle fold forms from the outer surface of the inner fold after metamorphosis and that the initial unfolded mantle margin may represent a common condition among bivalves. The first outgrowth process, which gives rise to the outer and inner folds, and the emergence of the pallial musculature and innervation occur during larval stages, highlighting the importance of the larval period for mantle margin morphogenesis in Bivalvia.

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Wood-boring bivalves of the families Teredinidae and Pholadidae are reported for the first time in Paraíba State, north-east Brazil. During one year, molluscs were collected from mangrove tree logs and from wood panels, along a salinity gradient. Four teredinid (Neoteredo reynei, Teredo bartschi, Nausitora fusticula, Bankia fimbriatula) and one pholad species (Martesia striata) were found.

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• Abstract: A survey for bivalves (Teredinidae) at several sites in the Escuro River andComprido River at mangrove regions in Praia Dura, Ubatuba, SP was conducted. Nausitora fusticula was the most abundant species found in all collection sites at the border of Comprido River meaning that the species was well adapted to the intertidal regions and to the large variation in salinity (O to 33 S). N. fusticula was found with Bankia fimbriatula, Bankia gouldi andBankia rochi at the mangrove region in contact with the water. At the regions less influenced by the tides N. fusticula occurred with Neoteredo reynei and few specimens of the genus Bankia already cited. The species ofTeredinidae was found at the maximum limit of penetration ofthe sea water during the high tides. When the salinity was lower neither Bankia species nor Neoteredo reynei occurred, but Psiloteredo healdi and N. fusticula were found.• Resumo: Realizou-se o levantamento e estudou-se a distribuição das espécies de

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

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The present work focuses on 12 taxa of the genus Centropyxis Stein, 1857 to explore the conflict between traditional and contemporary taxonomic practices. We examined the morphology, biometry, and ecology of 2,120 Centropyxis individuals collected from Tiete River, Sao Paulo, Brazil; with these new data we studied the consistency of previously described species, varieties, and forms. We encountered transitional forms of test morphology that undermine specific and varietal distinctions for three species and nine varieties. Biometrical analyses made comparing the organisms at the species level suggest a lack of separation between Centropyxis aculeata and Centropyxis discoides, and a possible distinction for Centropyxis ecornis based on spine characteristics. However, incongruence between recent and previous surveys makes taking any taxonomic-nomenclatural actions inadvisable, as they would only add to the confusion. We suggest an explicit and objective taxonomic practice in order to enhance our taxonomic and species concepts for microbial eukaryotes. This will allow more precise inferences of taxon identity for studies in other areas.