Abstract A total of 38 freshwater brachyuran species occur in Brazil, of which 79% are distributed in the northern region. However, for only two species of freshwater crabs are descriptions available for their juveniles. The importance of these studies lies in understanding of life-cycle aspects as well the potential elucidation of phylogenetic relationships within the group because the characters are usually solely based on adult specimens. The morphology of the first juvenile stage of the Dilocarcinus septemdentatus (Herbst, 1783) is described and illustrated for the first time based on specimens hatched by an ovigerous female collected in the northeastern region of the Brazilian Amazon. Juveniles of Dilocarcinus pagei Stimpson, 1861 and D. septemdentatus have one flagellar segment on the exopod of the first maxilliped while the only described juvenile of an unidentified species of Trichodactylus Latreille, 1828 has two. Dilocarcinus septemdentatus differs from other congeneric species mainly in the number of setae on the antennae and number of segments of the mandibular palp. Variations in the number of segments and aesthetascs enable the comparison between the juveniles of D. septemdentatus with those of other Brachyuran species previously studied and suggest possible adaptations to freshwater environments.

ABSTRACT: The abundance and distribution of larval phases of the Portunidae found in the estuary of the Patos Lagoon and the coastal region were studied during two years (1995 and 1999). A conical net (165 cm long, 60 cm mouth, and 330 µm mesh) equipped with a flowmeter was towed for three minutes at 2 knots at six stations within the estuary and four stations in the coastal region. Samplings were carried out on the surface and near the bottom. At each sampling location, the salinity and temperature were also recorded. In 1995, the zoeae of Arenaeus cribrarius (Lamarck, 1818), Callinectes sapidus Rathbun, 1896 and Achelous spinicarpus Stimpson, 1871 were caught, resulting in a total abundance of 121.98 ind.100 m-3 (90.95 ind.100 m-3 on the surface and 31.03 ind.100 m-3 near the bottom). A total of 452.27 ind.100 m-3 were caught in the megalopa phase (13.49 ind.100 m-3 on the surface and 438.78 ind.100 m-3 near the bottom). In 1999, only zoeae of C. sapidus were caught, resulting in a total abundance of 419.78 ind.100 m-3 (386.98 ind.100 m-3 on the surface and 32.8 ind.100 m-3 near the bottom). Megalopae of these three species were caught, resulting in a total abundance of 179.91 ind.100 m-3 (25.38 ind.100 m-3 on surface and 154.53 ind.100 m-3 near the bottom). Summer was the season with the highest abundance of larvae in both years. During spring and summer, spawning was observed in the estuarine region of the Patos Lagoon.

O objetivo do presente estudo é a elaboração de uma chave de identificação ilustrada das espécies de Brachyura que ocorrem no estuário da Lagoa dos Patos e sua região costeira adjacente. A chave abrange espécies as quais foram coletadas mensalmente, usando uma rede de plâncton (165 cm de comprimento, 60 cm de boca e 330 µm de malha). As amostragens foram realizadas na superfície e fundo. Os especimens foram identifcados mediante comparação com larvas cultivadas em laboratório e com descrições já existentes. A chave utiliza caracteres que não sofrem grandes transformações ao longo do desenvolvimento, e a utilização de figuras para ilustrar a chave permite a não especialistas facilmente identificar as espécies.

The goal of this study is to provide an illustrated identification key to distinguish zoeal phase of Brachyuran larvae that occur in the estuarine and nearby coastal region of the Patos Lagoon. The key includes species, collected monthly, using a conical net (165 cm long, 60 cm mouth and 330 µm mesh). Sampling was carried out on surface and deep waters. The identification was based on specimens reared under laboratory conditions as well as from previous published studies. This key was constructed upon external morphological characters, easy to observe under a stereomicroscope and moreover, the presentation of figures allows a non-specialist to make identifications more easily.

The larval development of Cyrtograpsus angulatus Dana, 1851 was studied in laboratory through eggs hatched from ovigerous females collected in mole of Rio Grande, Rio Grande, State of Rio Grande do Sul, Brazil. Three experiments (A, B, C) were carried out involving 250 larvae, derived from three ovigerous females. The experiments A and B, were carried in a climatically box with temperature among 22 and 25ºC, and salinity among 32 and 34‰. The experiment C in a room without controlled temperature, in a constant salinity of 30‰. The larvae were maintained individually and food consisted of rotifers Brachionus plicatillis Müller, 1786 and microscope algae Tetraselmis sp. The development of C. angulatus Dana, 1851 comprises five stages of zoea and one megalope. The main morphological characters that allow the identification of the first stages of C. angulatus, are analyzed with respect to the other Brazilian species of the family Grapsidae.