To assess and analyse accurately their geographical distributions, fiddler crabs (Uca) from the Atlantic coast of Brazil were studied using field collections, museum specimens and literature reports. More than 7000 specimens of ten Uca species were collected across five coastal biomes from 63 sites on the Atlantic coast of South America between the Brazilian States of Amapá and Santa Catarina in 2009 and 2010. Based on our analyses of mouthparts and habitat osmolality (=salinity), each species seems to prefer a particular niche defined by a specific array of physical factors. The species' distributions form four geographical patterns along the South Atlantic coast; however, the different species do not occur uniformly within each biome. Most common are U. (M.) rapax, U. (L.) leptodactyla, U. (B.) thayeri and U. (U.) maracoani with the relative abundance of each varying among the biomes according to habitat availability. Owing to their high constituent diversity, two geographical areas are candidates for biological conservation efforts. Considering fossil records, molecular clocks, oceanic hydrology and plate tectonics over the last 65 million years, the biogeographical patterns of the extant species can be used to reconstruct an evolutionary scenario for Uca in the tropical and temperate zones of the western Atlantic Ocean.

The composition and structure of a molluscan assemblage inhabiting an outcrop with a coralligenous community was studied in southern Spain. A total of 117 molluscan species were identified, with gastropods as the dominant group. Calyptraea chinensis was the dominant species and the family Conidae presented the highest number of species. The Shannon–Wiener diversity index and the Evenness showed non-significant changes between cold and warm months, displaying high values (~4 bits and ~0.8 bits respectively). Some of the dominant and/or frequent species are strictly associated with coralligenous-building organisms, such as Neosimnia spelta with gorgonians. Regarding trophic guilds, carnivores are the dominant group, followed by filter feeders due to the high abundance of C. chinensis. Regarding biogeographical distributions, most of these species (<95%) are widely distributed in European waters, the number of strictly Mediterranean species being very low. The Alboran Sea represents the distributional limit towards the Mediterranean for some species found in this bottom, such as the Atlantic Bela powisiana. Rocky–coralligenous bottoms are scarce in the western Alboran Sea but support a high species richness molluscan assemblage, displaying higher diversity values than the surrounding soft bottoms and increasing the biodiversity at local scale. This high biodiversity is partly explained by the coexistence of different taxa with contrasting biogeographical affinities promoted by the geographical location of the area. Due to this, conservation efforts should be required to protect this stretch of coastline where one of the most biodiverse invertebrate assemblages along the European coasts can be found.