Abstract Geometric morphometric methods are powerful tools to discriminate between closely related ostracods taxa as well as to study the relationship between their morphological variations, taxonomy and paleoecology. In this study, valve outline analysis allows the discrimination between the non-marine ostracod C. silvestrii and R. whatleyi juveniles, pointing out differences in the posterior valve area and surface ornamentation. Modern female specimens of C. silvestrii from 23 sites located in a spatial transect (41 to 51 °S) exhibited extensive morphological variability, on the basis of which three morphotypes (acuminated, transitional, subtruncated) were determined. Multivariate analyses showed that acuminated and transitional shapes are not arranged in groups but the subtruncated morphotype, previously described as E. cecryphalium, seems to be associated with low water conductivity (372 µS cm-1), dominant cold (5 ºC) and windy (8.6 m s-1) climatic conditions. The fossil cluster which included nine cores spanning the last 15.6 kyr, only covered acuminated and transitional shapes, which may indicate that these lineages might be older than the subtruncated morphotype. In addition, morphological differences between reproduction modes suggested that parthenogenetic females exhibit de posterior margin more acuminate than sexual females. These results set the ground for more precise ecological and paleoenvironmental studies in Patagonia.

Abstract In order to characterize Patagonian (Argentina) ecoregions using non-marine ostracods, their associations in 69 environments were assessed. Twenty eight taxa were recorded, including 12 endemic of the Neotropical region. Our results indicate that Patagonian ostracods are mainly influenced by electrical conductivity (EC), altitude, pH, and temperature; and shows a correlation with Argentinian ecoregions. Assemblage I is composed of sites located at high altitude in the Andean Patagonian forest ecoregion. Host waters have low temperature, EC and pH, and support as representative species Cypris pubera, Eucypris virens, Bradleystrandesia fuscata, Tonacypris lutaria and Amphicypris nobilis. Assemblage II, related to mid-altitude environments in the Patagonian Steppe ecoregion, thrived in waters with moderate to high EC, and alkaline pH values. Dominant species includes Limnocythere rionegroensis, L. patagonica, E. virgata, Riocypris whatleyi, Riocypris sarsi, Newnhamia patagonica, Kapcypridopsis megapodus, Ilyocypris ramirezi and Penthesinelula incae. Assemblage III inhabited environments within Monte and Espinal ecoregions, situated in the eastern part of the study area at low altitude, EC moderate and temperate waters, supporting Heterocypris hyalinus, Amphicypris argentinensis, Sarscypridopsis aculeata, Cypridopsis vidua, Herpetocypris intermedia and Chlamidotheca incisa. Our results indicates that Argentinian Patagonia hosts a diverse ostracod fauna and highlights their capacity as proxies in ecological and palaeoenvironmental studies.

The analysis of recent benthic foraminifera from the continental shelf and San Matías Gulf is presented. Quantitative analysis was performed using methods from compositional data analysis theory. Principal Components Analysis, Cluster analysis and Geographic Information System (GIS) were used to infer a) six groups of species that respond to oceanographic conditions, four of which were related to coastal waters and the others could be influenced by the Malvinas current system; b) the relationship between 13 species and the water temperature, bottom sediments, and energetic conditions of the area c) a correlation between Cibicides dispars/Bulimina patagonica and Cibicides mckannai/Bulimina patagonica and water temperature.

Se presenta el análisis de foraminíferos bentónicos en sedimentos superficiales de un sector de la Plataforma Continental Argentina y el golfo San Matías. El estudio cuantitativo se efectuó empleando métodos de análisis estadístico de datos composicionales. Mediante el Análisis de Componentes Principales (ACP), Análisis de Agrupamiento y Sistema de Información Geográfica (SIG) se pudo inferir: a) la presencia de seis grupos de especies cuyas características responderían a las condiciones oceanográficas del lugar, cuatro de ellos indicarían el predominio del sistema de agua costera y los dos restantes, la influencia de la corriente de Malvinas; b) la vinculación entre las variaciones conjuntas que experimenta la composición de 13 especies con la temperatura del agua, las características del fondo y las condiciones energéticas en el área y c) la correlación existente entre las relaciones Cibicides dispars/Bulimina patagonica y Cibicides mckannai/Bulimina patagonica y la temperatura del agua.

Fifty species of benthic foraminifera from a core of the Argentine Continental Shelf were identified. Elphidium discoidale (d'Orbigny), Buccella peruviana campsi (Boltovskoy), Quinqueloculina patagonica d'Orbigny and Quinqueloculina seminula (Linné) were the dominant species. The association is characteristic of inner shelf environments. Qualitative and quantitative analyses allow the recognition of a lower zone with an assemblage typical of restricted environments, and an upper zone which, according to foraminifers, reflects a change towards normal marine conditions. The core was deposited during the post last glacial maximum transgression, about 10.000 yr B.P.

Se reconocen 50 especies de foraminíferos bentónicos recuperados de un testigo proveniente de la cuenca del Colorado. Predominaron Elphidium discoidale (d'Orbigny), Buccella peruviana campsi (Boltovskoy), Quinqueloculina patagonica d'Orbigny y Quinqueloculina seminula (Linné). La asociación de especies encontrada indica un ambiente marino de plataforma interna. A partir de análisis cualitativos y cuantitativos se pudieron distinguir dos tramos. En el tramo inferior se infiere un ambiente restringido, mientras que en el tramo superior se observa una tendencia al establecimiento de las condiciones marinas normales. Los sedimentos del testigo se habrían depositado durante la transgresión del último máximo glacial, hace aproximadamente 10.000 años B.P.

Ostracods and charophytes from the Desencuentro Formation (La Rioja Province, Argentina) are described and illustrated. The association has low diversity with six ostracod taxa: Eucypris sp., Darwinula sp., Cyamocytheridea sp., Cyprideis salebrosa hartmanni Ramírez, Limnocythere aff. L. reticulata Sharpe, Limnocythere sp. and two charophytes: Chara zeylanica s. l. Klein ex Willdenow and Chara musacchioi García sp. nov. The availability of twenty well preserved gyrogonites of Chara musacchioi sp. nov. allowed to observe the intra-populational morphological variability, to relate the new species with the extant Chara hornemannii Wallman, and to conclude that it is a new species. The assemblage indicates a calm aquatic environment with oligohaline to mesohaline water, with a possible input of fresher water, in a tropical to subtropical area, with mean temperature of about 15-20°C.

Se describen e ilustran los ostrácodos y carófitos de la Formación Desencuentro, provincia de La Rioja, Argentina. La asociación muestra baja diversidad con seis taxones de ostrácodos: Eucypris sp., Darwinula sp., Cyamocytheridea sp., Cyprideis salebrosa hartmanni Ramírez, Limnocythere aff. L. reticulata Sharpe, Limnocythere sp., y dos especies de carófitos: Chara zeylanica s. l. Klein ex Willdenow y Chara musacchioi García sp. nov. El hallazgo de veinte girogonites bien preservados de Chara musacchioi permitió evaluar su variabilidad morfológica, establecer su relación con la especie actual Chara hornemannii Wallman, y arribar a la conclusión de que se trata de una nueva especie. Estos taxones indican un ambiente acuático de aguas tranquilas oligohalinas a mesohalinas, con posible aporte de agua dulce, en un área tropical a subtropical, con temperatura media de alrededor de 15-20°C.

Qualitative, quantitative and statistic analysis on samples of surface sediments from San Matías Gulf, Río Negro Province, Argentina, reveal a relationship between the type of substrate- depth and characteristics and distribution of the benthic foraminifer Nonionella auris (d´Orbigny). The study suggests that the development of this species is favoured in low energy and deep environments with muddy substrates.

Se estudia la influencia del tipo de sedimento y la profundidad en la distribución y desarrollo del foraminífero bentónico Nonionella auris (d'Orbigny). Se analizaron muestras de sedimentos superficiales provenientes del golfo San Matías, provincia de Río Negro, Argentina. Los estudios cualitativos, cuantitativos y estadísticos realizados sugieren que sitios con mayor profundidad, mayor contenido de fango y bajo nivel de energía propiciarían el desarrollo de esta especie.