A new species of Anoplodactylus was discovered in coral reefs from the State of Paraíba, northeastern Brazil. A. mirim sp. nov. is very small and is characterized for having 3 teeth on the cheliphores and a very small cement gland. It belongs to the A. pygmaeus complex, which contains very small species. A. batangensis is recorded for the first time along the Brazilian coast, and A. eroticus is recorded for the first time in the South Atlantic. We record the fifth known case of gynandromorphism, the fourth for Anoplodactylus, based on two specimens of A. eroticus.

Coastal ecosystems of northeastern Brazil have important biodiversity with regard to marine mollusks, which are insufficiently studied. Here we provide an inventory of mollusks from two sites in the estuary of the Paraíba River. Mollusks were collected in 2014 and 2016 on the coast and sandbanks located on the properties of Treze de Maio and Costinha de Santo Antônio. The malacofaunal survey identified 12 families, 20 genera and 21 species of bivalves, 17 families, 19 genera and 20 species of gastropods and one species of cephalopod. Bivalves of the family Veneridae Rafinesque, 1815 were the most representative, with a total of five species. Gastropods of the family Littorinidae Children, 1834 had the greatest species richness. The most abundant species were: Neritina virginea (Linnaeus, 1758), Brachidontes exustus (Linnaeus, 1758), Crassostrea brasiliana (Lamarck, 1819), Cerithium atratum (Born, 1778), Anomalocardia brasiliana (Gmelin, 1791), Parvanachis obesa (C. B. Adams, 1845), Phrontis polygonata (Lamarck, 1822), Littoraria angulifera (Lamarck, 1822), L. flava (King, 1832), Tagelus plebeius (Lightfoot, 1786), Echinolittorina lineolata (d'Orbigny, 1840) and Iphigenia brasiliensis (Lamarck, 1818). The results show that the study area has considerable species richness of Mollusca, requiring environmental monitoring in the region mainly due to the economic importance of some species to the local population.

In symbiotic crustaceans, host-use patterns vary broadly. Some species inhabit host individuals solitarily, other species live in heterosexual pairs, and even other species live in aggregations. This disparity in host-use patterns coupled with considerable differences in host ecology provide opportunities to explore how environmental conditions affect animal behavior. In this study, we explored whether or not symbiotic crustaceans inhabiting relatively large and structurally complex host species live in aggregations. We expected Periclimenes paivai, a small caridean shrimp that lives among the tentacles of the large and morphologically complex scyphozoan jellyfish Lychnorhiza lucerna, to live in groups given that the host traits above constraint host-monopolization behaviors by symbiotic crustaceans. We described the population distribution of P. paivai during a bloom of L. lucerna near the mouth of the Paraíba River estuary in Paraíba, Brazil. The population distribution of P. paivai did not differ statistically from a random Poisson distribution. Male shrimps were most often found dwelling on the surface of L. lucerna individuals as small groups (2-4 individuals), in agreement with expectations. Periclimenes paivai is a sexually dimorphic species with males attaining smaller average body sizes than females and exhibiting no elaborated weaponry (claws). Females, but not males, experience positive allometry in cheliped size and were found living solitarily in small but not large host individuals. The above suggest that females might be territorial or that they might be competing for resources (i.e., food) likely expected to impact their reproductive output. Our results agree, but only partially, with the idea that large and morphologically complex host species should harbor non-territorial gregarious symbiotic crustaceans. Symbiotic crustaceans represent excellent models to improve our understanding about the conditions driving the social behavior of marine organisms.

Records of pycnogonids from Uruguayan waters (south-western Atlantic) include 26 species cited from precise locations, and at least five other species based on unconfirmed records. Nearly half of the species in that fauna belong to the genus Nymphon (12 spp.). Most species (22) come from deep-water and were recorded and described by C. A. Child. Of these, at least twelve species have an extended Antarctic and Subantarctic distribution, showing the influence of these cold waters in the area; three others have a wide deep-sea distribution pattern. Five species are known only from the lower slope and abyssal basin off La plata river: Mimipallene Atlantis and four species of Nymphon. Records from coastal and shelf areas (four species) are poorly documented and should be the focus of future research. Of these, Colossendeis geoffroyi is considered endemic in the Southwest Atlantic between 34ºS and 40ºS, but presents clear Antarctic affinities. A small-sized species living in shallow waters, Pycnogonum cessaci, is here considered as cryptogenic.

The Brazilian coast is over 7000 km long. It is comprised of diverse environments such as reef, lagoons and mangroves. These diverse habitats support great biological diversity but, due to the extension of the coast, knowledge of the pycnogonid fauna is poor and fragmented. Records from Brazil began with Krøyer in the 1840s. Collections from Brazilian waters by the "H.M.S. Challenger" and "Vettor Pisani" expeditions were published by Hoek (1881) and Schimkewitsch (1888). For almost 50 years there were no further publications, until Marcus (1940c) published his comprehensive paper on the South American fauna. Publications peaked between the 1940s and 1960s, with papers by Marcus, Sawaya, Mello-Leitão, Corrêa, Du Bois- Reymond Marcus, Hedgpeth and Stock. Approximately 40 papers based on material from Brazilian waters were published at this time, which recorded 65 species for Brazil. The aim of the present work is to provide a checklist of the Brazilian pycnogonids while providing a historical review and a full account of the corresponding literature.

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IntroductionThe Brazilian littoral covers over 7300 km, reaching 8500 km when all the coastal contours are added (Silva, 1999;Ministério do Meio Ambiente, 2002). The coastline offers a large diversity of environments such as beaches, dunes, cliffs, estuaries, deltas, sandbanks, and islands (Pinheiro et al., 2008), as well as the only reef formation in the South Atlantic, which extends for 3000 km (Amaral and Jablonski, 2005). However, the marine invertebrate fauna remains insufficiently known in Brazil (Amaral and Jablonski, 2005). For some regions, sampling is simply nonexistent for a large number of taxa (Marques and Lamas, 2006). This applies particularly to the Pycnogonida.The study of the Pycnogonida in Brazil began in the 19th century with the expeditions "Challenger" (Hoek, 1881) and "Vettor Pisani" (Schimkewitsch, 1890). Despite these early beginnings, the study of Brazilian Pycnogonida was only continued in 1940 by Ernst Marcus, who published a catalogue of Pycnogonida from South America (Marcus, 1940). This remains, perhaps, the most important contribution for this region. Since the initial work by Marcus, several authors published on the fauna of Pycnogonida from Brazil. Between 1940 and 1970, at least 16 papers were published, mainly by Sawaya, Mello-Leitão, Corrêa, du Bois-Reymond Marcus, Zilberberg, and Zago. These papers recorded 65 species in total, belonging to 20 genera and 11 families (Lucena and Chistoffersen, 2018). This flow of papers led Stock (1992) to comment that the Brazilian littoral was well sampled for Pycnogonida. However, only seven papers deal with the pycnogonid fauna of northern and northeastern

This paper describes the epibiosis of Ostrea cf. puelchana on Callinectes exasperatus (Gerstaecker, 1856), both collected from the estuary of the Paraíba River, in the state of Paraíba, northeastern Brazil. The basibiont crab was captured using a trap installed in mangrove area at a depth of about 2 meters. The oyster was closely attached to the left side of dorsal carapace covering most of the epibranchial, mesobranchial and metabranchial regions. Possible advantages and disadvantages for both the epibiont and the basibiont are discussed. We believe that young O. cf. puelchana may avoid a variety of potential predators due to the considerable movement capacity of C. exasperatus and may also serve as a small protective shield for the basibiont. However, the oyster, which is a bivalve with an epifaunal lifestyle, is likely to be negatively affected, mainly due to burrowing activity of the crab. This is the first record of epibiosis between bivalves of the genus Ostrea Linnaeus, 1758 and crabs of the genus Callinectes Stimpson, 1860.