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Diplodon granosus was one of the first freshwater mussels to be described for South America. However, the status of the species was confusing for a long time, receiving different taxonomic treatments. In this paper, we redescribe the shell, with new data on the soft parts and information on the distribution and conservation of D. granosus, a rarely recorded species. The shell is thin, not inflated; the macrosculpture is composed only by granules that cover the whole shell, not forming bars; the microsculpture comprises short spikes. In the soft parts we highlight the few, weak and irregularly distributed lamellar connections of the outer demibranch and some features of the stomach, such as the distally enlarged minor typhlosole. There are records of D. granosus over a large area of South America, from Guiana to Argentina. However, most of these records are related to other species and the distribution of D. granosus is restricted to the north of South America in the basins of the Amazonas and Orinoco rivers, and coastal rivers in between. Despite this wide distribution, the species occurs in specific habitats, mainly streams (igarapés), resulting in an extremely fragmented occurrence. Thus, any disturbance to these habitats can threat this freshwater mussel. RESUMO Diplodon granosus foi um dos primeiros bivalves de água doce descritos para a América do Sul. Contudo, o status dessa espécie foi confuso por um longo tempo, recebendo diferentes tratamentos taxonômicos. Neste estudo, apresentamos a redescrição da concha, assim como novos dados da anatomia das partes moles, e informações acerca da distribuição e conservação desta espécie raramente avistada. A concha é fina, não-inflada; a macroescultura é composta somente por grânulos que cobrem toda a concha, e não formam raios; a microescultura é composta por espinhos curtos. Nas partes moles, destacamos as poucas, fracas e irregularmente distribuídas conexões interlamelares da demibrânquia externa, assim como algumas características do estômago, como a tiflossole menor distalmente aumentada. Existem registros de D. granosus em uma grande área da América do Sul, da Guiana até a Argentina. Contudo, muitas destas ocorrências são relacionadas com outras espécies, estando D. granosus restrita às bacias dos rios Amazonas e Orinoco, e a rios costeiros entre essas duas bacias. Apesar desta aparente ampla distribuição, a espécie ocorre em habitats específicos, principalmente riachos (igarapés), resultando em uma distribuição fragmentada. Assim, qualquer modificação nestes ambientes pode ameaçar esta espécie.

New collection work in Mount Flora, Hope Bay, Antarctic Peninsula, has confirmed the presence of bivalve moulds in the Jurassic Mount Flora Formation. In contrast to a twenty-first century article claiming to report the first discovery of fossil freshwater molluscs in Antarctica, evidence of these molluscs was first reported for Antarctica more than 110 years ago by J. Gunnar Andersson. The bivalve was formally described and named some 50 years later, by Camacho, as Antediplodon esperanzaensis. The species was subsequently transferred to the genus Diplodon for unknown reasons. Here, we illustrate specimens from the same locality for the first time with photographs, considering them Unionida incertae saedis, in view of the absence of diagnostic characters. In fact, two morphotypes are present, one elongated, very similar to the nominal species A. esperanzaensis, and another one subelliptical in shape. Fil: Martínez, Sergio. Universidad de la República; Uruguay Fil: Scasso, Roberto Adrian. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina Fil: Elgorriaga, Andres. Museo Paleontológico Egidio Feruglio; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Capelli, Ignacio Andrés. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina Fil: del Valle, Rodolfo. Ministerio de Relaciones Exteriores, Comercio Interno y Culto. Dirección Nacional del Antártico. Instituto Antártico Argentino; Argentina Fil: Puerta, Pablo. Museo Paleontológico Egidio Feruglio; Argentina Fil: Lirio, Juan Manuel. Ministerio de Relaciones Exteriores, Comercio Interno y Culto. Dirección Nacional del Antártico. Instituto Antártico Argentino; Argentina Fil: Rodriguez Amenabar, Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentina. Ministerio de Relaciones Exteriores, Comercio Interno y Culto. Dirección Nacional del Antártico. Instituto Antártico Argentino; Argentina

During the last 40 years time lapse photography has become a strong tool for in situ observations of marine and freshwater wildlife. We compared the validity of two low cost camera systems to analyze the filtration activity of Diplodon chilensis (Gray, 1828), the most common freshwater bivalve in southern Chile. One camera system (Nikon D300) was connected with an external flash, whereas the other system (GoPro Hero 3+) contained a permanent video light source. Size change of the total area of the exhalant siphon (ESA) of Diplodon individuals was used to track activity changes over time. Each ESA is expressed as the percentage of the maximum siphon opening of the corresponding specimen. The siphon of D. chilensis was completely closed for 3.4% ± 5.2% (mean ± SD) of the recording time and it shows a nearly completely opened siphon for 42.7% ± 22.9% of the recording time. The mean siphon opening was 68.3% ± 26.5% of its potential opening area. Although a red filter (permeable to wavelengths above 600 nm ) was placed in front of the video light source, the mobile fauna, especially Aegla abtao (Schmitt, 1942) and unidentified small fishes were highly attracted by the permanent light, whereas this effect was not visible when a flash light in intervals of 2 min was used. We conclude that both low cost cameras are very suitable for in situ time lapse observation of freshwater clams.

This paper presents the levels and distribution of 210Po in different compartments of a coastal lagoon on the east coast of Uruguay (South America). Activity concentrations of 210Po have been obtained in different matrices, such as water, superficial sediments, clams (Diplodon sp.), freshwaters snails (Pomacea sp.), zooplankton, and fishes (Jenynsia sp.), collected at different points of the lagoon and during several sampling campaigns. In addition, the organic matter content of the sediment was determined to study the variation of 210Po along the lagoon. The activity concentrations of 210Po in the water samples are in the range between 1.1 ± 0.2–3.5 ± 0.4 mBq/L while in the sediment samples vary between 17.1 ± 1.4 and 540 ± 12 Bq/kg, DW. In the case of biota, the ranges obtained were 182 ± 5–265 ± 6 Bq/kg, DW in clams and 134 ± 4–1245 ± 16 Bq/kg, DW in snail samples. A good correlation of 210Po with the organic fractions of the sediment was observed (r = 0.8798, p-value < 0.001), being obtained high values for the distribution coefficient Kd (104 -105). In the biota samples, a clear difference was observed in the 210Po concentration values in both species, mainly due to the different feeding habits of both aquatic organisms, as it is reflected in the associated concentration ratios (CR). In this paper, a good set of results of 210Po, Kd, and CR have been obtained in different matrices, enhancing the limited archives available for modelers concerning these parameters for 210Po and freshwater systems., This work was supported by National Agency for Research and Innovation (ANII) through PhD (POS_NAC_2016_1_130091) and movility fellowships (MOV_CA_2019_1_156608), and Comisión Sectorial de Investigación Científica (CSIC), and Programa de Desarrollo de las Ciencias Básicas (PEDECIBA).

En este trabajo se discute el rol de los moluscos fluviales en la subsistencia de los grupos cazadores-recolectores del tramo final de la cuenca del río Paraná, especialmente de Diplodon (Rhipidodonta) variabilis. Se analiza su disponibilidad ambiental, la distribución de tallas en un banco actual y las relaciones alométricas entre los pesos del tejido blando y del exoesqueleto. Paralelamente, se describe la posición de este bivalvo dentro del ranking de las presas locales, y su incorporación en el proceso regional de diversificación e intensificación de la subsistencia durante el Holoceno tardío. Luego, con los resultados obtenidos, se analizan los conjuntos arqueomalacológicos recuperados en los sitios Punta Canal (900 ± 80 años 14C AP), La Bellaca sitio 1 (1110 ± 70 años 14C AP) y Cerro Lutz (730 ± 70 / 953 ± 47 años 14C AP), donde se discuten las actividades de recolección, la selectividad dimensional y el aporte neto de alimento. Finalmente, se analizan las señales isotópicas transferidas a los humanos relacionados con la ingesta de esta especie. This paper discusses the role of fluvial mollusks in the subsistence of the hunter-gatherer groups of the Lower Parana basin, especially the bivalve Diplodon (Rhipidodonta) variabilis. Their environmental availability, the distribution of sizes in a colony and the allometric relationships between the weights of the soft tissue and the exoskeleton are analyzed. In parallel, the position of this bivalve in the ranking of local prey and their incorporation into the regional process of diversification and intensification of subsistence are analyzed. Based on the results obtained, the archeomalacological assemblages recovered at Punta Canal sites (900 ± 80 years 14C BP), La Bellaca site 1 (1110 ± 70 years 14C BP) and Cerro Lutz (730 ± 70/953 ± 47 14C BP years) are discussed. Finally, the isotopic signals transferred to humans related to the intake of this species are analyzed. Fil: Loponte, Daniel Marcelo. Secretaría de Cultura de la Nación. Dirección Nacional de Cultura y Museos. Instituto Nacional de Antropología y Pensamiento Latinoamericano; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Parisi, Florencia Silvia. Secretaría de Cultura de la Nación. Dirección Nacional de Cultura y Museos. Instituto Nacional de Antropología y Pensamiento Latinoamericano; Argentina Fil: Liotta, Jorge. Museo de Ciencias Naturales Antonio Scasso; Argentina Fil: Wagner, Mario. Secretaría de Cultura de la Nación. Dirección Nacional de Cultura y Museos. Instituto Nacional de Antropología y Pensamiento Latinoamericano; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Acosta, Alejandro Alberto. Secretaría de Cultura de la Nación. Dirección Nacional de Cultura y Museos. Instituto Nacional de Antropología y Pensamiento Latinoamericano; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

The knowledge on diet composition of the freshwater mussel Diplodon enno (Ortmann) would aid in its culture and propagation allowing, this way, the replacement of natural endangered populations in Brazil. Microalgae are the main food source for captive mussels and unionids have displayed an ability to sort algae based on the cellular characteristics prior to ingestion. The main objective of the present work is to analyze the phytoplankton composition of the water from and of the gastrointestinal contents of the mussel D. enno, as an initial step for development of a suitable rearing diet. Therefore, water samples and bivalve specimens were collected from S. Francisco River, city of Paulo Afonso, Bahia, Brazil. The microalgal composition found in water and stomach/gut content samples was very diverse being represented by the following divisions: Cyanophyta, Chlorophyta, Dinophyta and Heterokontophyta (Diatoms). Concerning the relative abundance of microalgae divisions, it is possible to state, for the water and gastrointestinal contents, that Cyanophyta represents 15% and 14%, Chlorophyta 54% in both, Heterokontophyta 31% and 27% and Dinophyta 0% and 5%, respectively. According to the Brazilian CETESB criteria for phytoplankton species classification, 50% of Cyanophyta and 15% of Chlorophyta species observed in the water samples were classified as “very frequent”, as were 68% of Heterokontophyta and 33% of Chlorophyta species in the gut/stomach tract samples. Focusing at a species level, although in the water only Coelastrum sp. and Chroococcus sp. were observed in 100% and 75% of the samples, respectively, in the gastrointestinal tract the species Staurastrum sp., Aulacoseira sp., Scenedesmus sp. and Fragilaria crotonensis occurred in 80% to 100% of the samples. The present results showed that D. enno feeds not only on small chlorophytes microalgae, due to their convenient size that facilitates higher feeding rates, but also on large size diatoms, due to a possible nutritional advantage for the bivalves. Thus, a diet composed by large diatoms and small chlorophytes microalgae may be considered as the most reasonable for the maintenance of D. enno populations.

The Santa Cruz Formation (Early–Middle Miocene) is one of the most widespread sedimentary units of the Argentine Patagonia. This unit contains an abundant and taxonomically diverse fossil vertebrate fauna, especially in mammals. Thus, the paleoecological and paleoenvironmental information derives mainly from the analysis of the vertebrate assemblages, as well as from the ichnological and paleobotanical evidence. The record of freshwater bivalves assigned to the species Diplodon cf. colhuapiensis Ihering, 1903 from the Santa Cruz Formation, collected in the locality of Barrancas Blancas (Estancia Santa Lucía), at Río Santa Cruz, allows us to infer the particular paleoenvironmental conditions setting during the deposition of the bearing levels. Considering this record, we propose that Diplodon, which was originally assigned to the “Sehuenense stage” (piso sehuenense of F. Ameghino), could have come from the Early–Middle Miocene of the Santa Cruz Formation. In this sense, the specimens referred to Diplodon cf. colhuapiensis suggest the existence of an established community of Hyriidae mollusks at the upper-middle levels of the Santa Cruz Formation. The presence of freshwater bivalves suggests that the depositional environment of this unit included the existence of water courses. The identification of the genus in the Santa Cruz Formation validates its presence in the Early Miocene and extends its southern distribution to the latitude of Río Santa Cruz (~ 50º S)., La Formación Santa Cruz (Mioceno Temprano–Medio), es una de las unidades sedimentarias más extendidas de la Patagonia argentina. Esta unidad contiene una gran abundancia y diversidad taxonómica de vertebrados fósiles, especialmente de mamíferos. De esta manera, la información paleoecológica y paleoambiental proviene principalmente del análisis de la asociación de vertebrados, como también la evidencia icnológica y paleobotánica. El registro de bivalvos de agua dulce asignados a la especie Diplodon cf. colhuapiensis Ihering, 1903 de la Formación Santa Cruz, recolectado en la localidad Barrancas Blancas (Estancia Santa Lucía), cerca del Río Santa Cruz, permite inferir las condiciones paleoambientales de la depositación de sedimentos de los niveles portadores de los especímenes. Teniendo en cuenta estos restos, proponemos que el material de Diplodon originalmente asignado al “piso Sehuenense” (piso sehuenense de F. Ameghino), podrían provenir del Mioceno Temprano–Medio de la Formación Santa Cruz. En este sentido, el registro de Diplodon cf. colhuapiensis confirma la existencia de una población establecida de moluscos de la familia Hyriidae en los niveles medio-altos de la Formación Santa Cruz. La presencia de bivalvos de agua dulce, probablemente habitando canales fluviales, sugiere la existencia de cursos de agua bien desarrollados en el ambiente depositacional de la unidad. La identificación del género en la Formación Santa Cruz valida su presencia en el Mioceno Temprano y extiende su distribución sur a la latitud actual del Río Santa Cruz (~ 50º S)., Facultad de Ciencias Naturales y Museo

O objetivo deste estudo foi analisar a frequência por classes de comprimento e a organização histológica das gônadas de Diplodon ellipticus em um lago artificial localizado no município de Morretes-PR. Foram realizadas seis campanhas amostrais bimestrais no período de julho de 2009 a maio 2010, com captura de 150 espécimes. O comprimento total das conchas foi medido para determinação das frequências de classes de comprimento e foi realizada análise da presença de marsúpios nas brânquias. A determinação do sexo foi realizada por meio da análise histológica de secções transversais da massa visceral. Foram registradas oito classes de comprimento, com intervalo de 9 mm, e a classe modal variou entre 50 a 59 mm. A população é predominantemente dioica, com ocorrência de espécimes hermafroditas em baixa frequência. Marsúpios foram registrados em fêmeas (86%) em todas as coletas amostrais e em dois exemplares hermafroditas. Análises histológicas demonstraram que a espermatogênese e ovogênese ocorrem ao longo do ano, indicando que D. ellipticusapresenta uma estratégia que proporciona uma reprodução contínua, com picos de liberação de gloquídios.

Unionida is the most diverse clade of freshwater bivalves. Among the groups occurring in South America, one with the highest number of species is Rhipidodontini (Hyriidae, Unionida, Paleoheterodonta, Bivalvia). However several issues remains on taxonomy and systematic of this group, leading to problems on species identification, description, as also as a limiting factor to other type of studies (e.g., ecology, conservation,…). In this paper is presented a synthesis of available knowledge about Diplodon Spix in Wagner, 1827 and Rhipidodonta Mörch, 1853 in South America, as a first step in order to a better understating of Rhipidodontini. The evaluation of different authors exposes the little agreement between them that resulted in a sort of divergent taxonomical opinions. Some comments on ecology, conservation and habitat preferences were made. This work can also encourage future research on taxonomy, systematic, ecology and conservation of freshwater mussels in South America. Resumo Unionida é o clado mais diverso de bivalves de água doce. Entre os grupos que ocorrem na América do Sul, um dos com maior número de espécies é Rhipidodontini (Hyriidae, Unionida, Paleoheterodonta, Bivalvia). Porém, diversas questões taxonômicas e sistemáticas ainda incidem sob este grupo, levando a problemas de identificação de espécies, descrição, entre outros, como também tem atuado como limitador de outros tipos de estudos (e.g., ecologia, conservação,..). Neste trabalho é apresentada uma revisão do conhecimento acerca dos gêneros Diplodon Spix in Wagner, 1827 e Rhipidodonta Mörch, 1853 na América do Sul como um primeiro passo para a melhor compreensão de Rhipidodontini. Avaliando-se diferentes autores, se torna claro a pouca concordância entre eles, resultando em opiniões taxonômicas divergentes. São feitos também alguns comentários sobre ecologia, conservação e preferências ambientais. Este trabalho também deve encorajar futuros trabalhos sobre a taxonomia, sistemática, ecologia e conservação de bivalves de água na América do Sul.

A mollusk assemblage with Anodontites aff. elongatus (Swainson), Anodontites trapesialis (Lamarck), Anodontites sp., Diplodon aff. delodontus Lamarck and the gastropod Pomacea aff. canaliculata Lamarck is described. This fauna, together with at least three species of the bivalve genus Neocorbicula Fisher, ostracods of the genus Cyprideis Jones and Charophyta indet. are from the Middle Miocene San Jose Formation, from the locality of Quebrada de Mal Paso, near Tolombon in the northern Santa Maria valley (Salta Province). The association would indicate tropical and/ or subtropical fresh water bodies, zoogeographically belonging to the Neotropic Region. Keywords: mollusks, San Jose Formation, Middle Miocene, Northwestern Argentina.

The glochidia of Diplodon (Diplodon) suavidicus (Lea, 1856), D. (D.) obsolescens F. Baker, 1914, Diplodon (Rhipidodonta) hylaeus (d'Orbigny, 1835), Prisodon obliquus Schumacher, 1817, Paxyodon syrmatophorus (Meuschen, 1781), Triplodon corrugatus (Lamarck, 1819, and Castalia ambigua Lamarck, 1819 were redescribed based on comparisons of external morphology and morphometric measurements of larval shells. The outline of the glochidial valves was classified into three types. The morphological comparison was based on light and scanning electron microscopy. Details of the shell, hooks and external sculpture allowed a redescription of the larvae, transferring D. suavidicus and D. obsolescens to the subgenus Diplodon and, within the Prisodontini, the genus Triplodon Spix, 1827 was separated from Prisodon Schumacher, 1817 and Paxyodon Schumacher, 1817. The glochidium of Prisodon obliquus is described for the first time. The larvae of the latter species and those of Paxyodon syrmatophorus present projecti...

The development of host fish techniques (in vivo) at the beginning of the 20th century, and the improvement of artificial culture media for in vitro culture of bivalves, provided an opportunity to identify the nutritional requirements needed to complete the life cycle of threatened freshwater bivalves. A freeze-dried extract of lambari, a Brazilian Tetra (Astyanax altiparanae), was used as an additive to the artificial culture medium M199 (Sigma®) to try to improve the survival of glochidia and the metamorphosis of Diplodon rotundus gratus and D. greeffeanus. We adjusted the pH of the culture medium to 6.8, the same value recorded at the collecting site of the bivalves. Glochidia were kept in an incubator at 18°C. 40% of D. rotundus gratus glochidia survived, and 20% reached metamorphosis after 22 days of incubation. For D. greeffeanus 50% of the glochidia survived with 15% undergoing metamorphosis after 22 days of incubation. These results suggest an increase in the post-metamorphic survival wit...

Freshwater mussels of the genus Diplodon (Unionida) are common inhabitants of lakes and rivers in South America, and have slow growth and long life spans. We established the annual periodicity of incremental shell growth in Diplodon chilensis patagonicus (d'Orbigny, 1835) and calculated growth rates at different ages, using internal ring counting supported by dyeing methods and δ 18 O isotope analyses, in two Patagonian populations (Lago Steffen and its effluent Rio Manso Inferior, Argentina). Longevities of ca. 90 years (Lago Steffen) significantly extend the life spans reported in the past. Growth rates for old individuals (>30 years) from both lake and river populations average 0.16 mm per year along the axis of minimal growth. We evaluated the seasonal periodicity of minor and trace elements (Mn, Mg, Sr, Ba, Na, S) in situ by Laser Ablation ICP-MS and Electron Probe Microanalyser analyses. Line-scans in a valve from Lago Steffen show that Mn, Sr and Ba are preferentially accumulated during the summer, while higher concentrations of Mg are found in the winter bands. Metal/Ca ratios may serve as long-term archives of environmental variables, e.g. metal concentrations in water, water temperature and primary productivity. Diplodon chilensis patagonicus valves exhibit excellent characteristics to construct an accurate chronological archive with time windows of up to around a century, resolving the environmental signal annually and even seasonally.

Larvae of Hysterothylacium use various invertebrates as intermediate hosts. Definite hosts include fish, birds, reptiles or marine mammals. This study describes the occurrence of Hysterothylacium (Nematoda, Anisakidae) larvae parasitizing the pericardic cavity of Diplodon suavidicus (Unioniformes, Hyriidae) specimens collected in the Amazon basin, Brazil. This is the first record of this nematode parasitizing freshwater bivalves in South America. The high prevalence, medium intensity and medium abundance suggest that D. suavidicus acts as intermediate host for Hysterothylacium species in that environment. © 2010 Elsevier Inc.

The diet and trophic relationships between the macroinvertebrates Phyllogomphoides joaquini Rodrigues Capítulo, 1992 and Coenagrionidae (Odonata), Chironomidae (Diptera), Diplodon delodontus (Lamarck, 1919) (Bivalvia: Hyriidae), and Pomacea canaliculata (Lamarck, 1822) (Gastropoda: Ampulariidae) and the fishes Pimelodella laticeps Eigenmann, 1917 (Heptapteridae) and Bryconamericus iheringii (Boulenger, 1887) (Characidae) in a temperate lowland lotic system in Argentina were assessed on the basis of gut contents and stable-isotope analyses. The feeding strategies were analyzed by the Amundsen method. Relative food items contribution for the taxa studied indicated a generalist-type trophic strategy. In macroinvertebrates, in general, the values of stable isotope confirmed the result of the analysis of gut contents. With the fish, stable-isotope analysis demonstrated that both species are predators, although B. iheringii exhibited a more omnivorous behaviour. These feeding studies allowed us to determine the trophic relationships among taxa studied. Detritus and diatoms were a principal source of food for all the macroinvertebrates studied. In La Choza stream the particulate organic matter is a major no limited food resource, has a significant influence upon the community., Instituto de Limnología "Dr. Raul A. Ringuelet"

Freshwater mussels from a small lake in southern (subtropical) Brazil are analized in their distribution and abundance. The mussels were sampled through transects using quadrats of 1 m‐2. The individuals were manually collected with SCUBA and free diving. Data on substrate type, percentual of plant cover and depth were also recorded. A total of 443 m‐2 were sampled in the lake. Four species of Unionacea (Diplodon charruanus, Anodontites trapesialis, Anodontites (cf.) patagonicus, Monocondylaea minuana) and two of Corbiculacea (Neocorbicula limosa and Corbicula fluminea) are registered. D. charruanus was the most abundant species, occuring in the overall substrates with the greatest mean density (ind. m‐2) in the muddy sand subset of the lake. The lowest mean density of this species is on the pure mud subset. M. minuana was restricted to a band of 1.0 ‐ 1.5 m of depth, sandy substrate. There are indicatives of a crash in the population of A. trapesialis. Only five individuals of A. (cf.) patagonicus were r...

Diplodon rhombeus fontainianus (Orbigny, 1835), belongs to the family Hyriidae Swainson 1840, the distribution of which is restricted to South America and Australasia. This species, endemic to Brazil, occurs in the central-southern geographical region, Upper Paraná Basin and Atlantic Microbasins Espirito Santo to Paraná states. The mollusk lives buried in muddy substrata, has similar sized adductor muscles, and is dioecious, lacking sexual dimorphism. The apertures are simple (type AII of Yonge, 1948, 1957) as in Diplodon rotundus gratus, Castalia undosa martensi, Castalia undosa undosa and mantle fusion is present only in the base of the exalant aperture. The inhalant aperture exhibits tentacles originating from the inner fold while the exhalant aperture has no tentacles. The ctenidia are type D (of Atkins, 1937). A well-developed marsupium is present in the inner demibranch. The association between the ctenidia and the labial palps belongs to category I (of Stasek, 1963). The stomach constitutes a type IV structure (of Purchon, 1958). The posterior sorting area (psa) presents two pouches in Diplodon rhombeus fontainianus. Among the Hyriidae, the presence of these pouches has also been described in several species of Hyriidae from South America. The organization of the gut in the visceral mass follows the same pattern seen in the Hyriidae already studied: Castalia undosa martensi, Castalia undosa undosa, Diplodon.rotundus gratus,Diplodon charruanus and Diplodon pilsbryi.

Se entregan antecedentes que establecen que Diplodon patagonicus (D'Orbigny 1835) señalado como especie presente en la región Neo tropica-Patagonia por Graf & Cummins (2007) corresponde aDiplodon chilensis patagonicus (D'Orbigny 1846) (sensu Haas 1969).

1. 1. The distribution of ceramide aminoethylphosphonate (CAEP) in microsomal membranes obtained from different tissues of the bivalve mollusc Diplodon delodontus was determined. 2. 2. The concentration of CAEP reached from 9 to 19% of the total microsomal polar lipids, depending on the kind of tissue. 3. 3. Palmitic acid was the main fatty acid in the ceramide moiety, followed by stearic and eicosamonoenoic acids. 4. 4. Artificial membranes were prepared with microsomal phospholipids or phospholipids plus sterols, with and without the addition of CAEP. 5. 5. It was shown that the phosphonate confers minor mobility to the membranes. This effect is more effective when the membrane contains the natural sterols and the phospholipids are unsaturated.

Conchological and anatomical studies of the glochidium of Diplodon martensi (lhering, 1893) were performed on samples collected in a small river, tributary from the Cai River, that belong to the Jacui River sub-basin in south-eastern Brazil. The parasitic development of the glochidium was observed in laboratory on a small cichlid fish Gymnogeophagus gymnogenys (Hensel, 1870).

1. 1. The dietary and inter-organ cholesterol transport in the hemolymph of the bivalve mollusc Diplodon delodontus , was studied. Plasma and hemocytes were obtained after feeding labeled cholesterol to animals or injecting it into the posterior adductor muscle. 2. 2. In both cases, cholesterol was incorporated either into plasma or hematic cells. 3. 3. Two plasmatic fractions differing in their hydrated densities were recognized as cholesterol carriers and were isolated. They have characteristics of high density (HDL) and very high density (VHDL) lipoproteins, respectively. 4. 4. The major lipids in the different classes of lipoproteins were free sterols in HDL and phospholipids in VHDL. 5. 5. Neither low nor very low density lipoprotein transporting cholesterol was detected.

1. 1. Composition of lipids and fatty acids from plasma and hemocytes separated from freshwater bivalve molluscs Diplodon delodontus were studied. In both hemolymph components phospholipids were the major lipids, but quantitative composition of phospholipids and fatty acids was different in hemocytes and plasma indicating specific functions. 2. 2. When molluscs were fed 14C fatty acids or 14C triacylglycerols, dietary fatty acids were principally transported by plasma and to a lesser extent by hemocytes. Labeled triacylglycerol was only found in hemocytes. 3. 3. When isolated blood cells were incubated with different 14C fatty acids or 14C trioleylglycerol, they fixed the majority of the label but were unable to esterify fatty acids or hydrolyze trioleylglycerol. 4. 4. At least five proteins were separated in plasma, the majority having a molecular weight higher than 200 × 103 daltons. 5. 5. Three plasma compounds with lipoprotein characteristics were recognized.

Fat digestion, absorption, and transport in the fresh water mollusc Diplodon delodontus were studied after 1 and 6 h of force-feeding ‘?�4C tnpalmitoylglycerol and l-'4C palmitic acid. In a 1 h period, the mollusc was able to hydrolyze more than 50%of the triacylglycerolto free acids monoacyl and diacylglycerols.Digestion and absorption was completed before the 6 h feeding, and most ofthe label was eliminated. Hydrolysis occurred primarily in the stomach. The mollusc absorbed the products of hydrolysis and apparently triacylglycerol molecules, too. During the period of tripalmitoylglycerol digestion (1 h), the labeled palmitic acid was transported by the hemolymph in the free acid, monoacylglycerol, and triacylglycerol fractions that were also the principal components found in the stomach. During the post absorption period (6 h) the label was principally bound to triacylglycerols. When 1-'4C palmitic acid was fed to D. delodontus, the acid was absorbed and the label transported ex clusively in the free acid fraction of the hemolymph during the first hour. At 6 h ‘?�—#75% was still transported as free acid and the rest as triacylglycerol. The free palmitic acid was incorporated in the soft tissues of the mollusc and slowly esterified to tn acylglycerols.

1. 1. The inter-organ transport of free fatty acids, triacylglycerols and phospholipids in the hemolymph, as well as their distribution in tissues of the bivalve mollusc Diplodon delodontus. were studied. 2. 2. Plasma, hemocytes and tissues were obtained 412hr after injecting labelled palmitic acid into the posterior adductor muscle. 3. 3. Labelled palmitic acid in the free form or esterified into triacylglycerols and phospholipids, was detected in both plasma and hemocytes. 4. 4. The free fatty acids and phospholipids are mainly transported by three plasma lipoproteins with low (LDL), high (HDL) and very high (VHDL) density characteristics, respectively. 5. 5. Triacylglycerols circulate in hemolymph preferably associated with hematic cells and, to a lesser extent, they are also transported by plasma lipoproteins. 6. 6. Highest specific radioactivities were observed in gills and digestive diverticula. They mainly correspond to the accumulation of free fatty acids and triacylglycerols.

1. 1. The composition of lipids and fatty acids of male and female gonads of D. delodontus at different sexual stages were studied. 2. 2. The main differences were found in the percentages of triacylglycerols, cholesterol esters and phospholipids. 3. 3. Female gonads with few immature gametes contained more triacylglycerolds and less phospholipids than male gonads in similar conditions. 4. 4. Spermatogenesis increased the sterol esters of male gonads. Oogenesis increased triacylglycerols and sterol esters of female gonads. Non-fertilized eggs contained a high percentage of triacylglycerols and a low percentage of sterol esters. 5. 5. The fatty acid composition of gonads was low in saturated fatty acids. The unsaturation was scattered in 16 : 1, 18 : 1, 20 : 1, NMI 22 : 2 and polyunsaturated acids of ω6 and ω3 families. Only 20 : 1 exceeds the 10% of total fatty acids. Similarly to other Diplodon species, the ratio of ω3 : ω6 acids was low and typical of fresh water molluscs. 6. 6. Oogenesis increased the proportion of palmitoleate, α-linolenate and oleate: stearate ratio. The change of the fatty acid composition was mainly produced in the triacylglycerols. The changes were not due to unsaturated fatty acid biosynthesis in the gonads. However, oocytes were able to elongate palmitic and stearic acids.