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The recently erected macrocnemic family Hydrozoanthidae comprises relatively few species recorded from tropical and subtropical regions. In the Atlantic Ocean, this family has been reported only from three locations: the Caribbean Sea, the Argentine continental shelf and the Cape Verde Islands. Based on a study of colonies collected during scuba diving at Alcatrazes Archipelago's main island (São Paulo State), south-eastern Brazil, a new species belonging to the genus Terrazoanthus is described as T. silveirai sp. nov. Vaga, Migotto & Kitahara. Morphological and ecological observations coupled with molecular analyses revealed a unique cnidome, a novel facultative association with sponges, and confirmed the phylogenetic position of this new species within Hydrozoanthidae. Our results represent the second record of Hydrozoanthidae and Terrazoanthus from the South-western Atlantic, expanding the sparse taxonomic knowledge of the order Zoantharia in this area. [ABSTRACT FROM AUTHOR]

We analysed hydromedusa assemblages of South America (from 22°S to 56°S and from 040°W to 080°W), their association with water masses and the influence of the life cycle on medusa distributions. The geographic distribution of 130 species of hydromedusae was compiled from literature reports (62 publications between 1913 and 2012). Seven areas were defined: Atlantic Magellanic, Argentinean, Pacific intermediate zone, Pacific Magellanic, Peruvian–Chilean, South Brazilian and Oceanic. The variance of the species–environment relationship was explained by depth and temperature. Distribution patterns of Atlantic hydromedusae are associated with neritic water masses, supporting previously proposed biogeographical provinces. Assemblages on the Pacific side of South America are under the influence of the Humboldt Current system, with a break in species distribution around Chiloé Island. Only the oceanic assemblage contained the same species in both the Pacific and Atlantic zones. We found that meroplanktonic medusae contributed more to define the neritic assemblages, while the oceanic assemblage was better defined by holoplanktonic medusae. Therefore, our data suggest that meroplanktonic hydromedusae appeared to be more restricted in distribution than holoplanktonic ones. [ABSTRACT FROM PUBLISHER]

The Antarctic–Patagonian genus Abietinella, comprising two known species, Abietinella operculata (Jäderholm, 1903) and Abietinella grandis (Vanhöffen, 1910), is reviewed. The holotype of Abietinella operculata is fully redescribed, including morphometry and cnidome, unknown up to now. Its distinctive characters are the growth habit, hydrothecal shape and, most important, the presence of a dish-shaped operculum attached to the adcauline side of the hydrothecal aperture. We corroborate its conspecificity with A. grandis and, therefore, the monotypic condition of Abietinella. [ABSTRACT FROM AUTHOR]

The commensal hydroid Eutima sapinhoa Narchi and Hebling, 1975 lives attached to the mantle, gills, labial palps and foot of the bivalve Tivela mactroides . The solitary polyps bud off medusae that become free, leaving the host through the exhalant water current. Newly liberated medusae were cultivated in the laboratory, attaining 7.8 mm in bell height, 13.3 mm in diameter and having eight marginal tentacles, while developing the typical eutimid medusa characters of a long peduncle, four radial canals and marginal statocysts with many statoliths. Eutima sp., previously reported from Florida, USA, is probably referable to Eutima sapinhoa . Like the other bivalve-inhabiting species of Eutima [ E. ostrearum ( Mattox and Crowell, 1951 ) and Eutima sp.] from the Atlantic Ocean, Eutima sapinhoa has no trace of marginal cirri, thereby differing from the eutimid medusae of the Pacific Ocean. [ABSTRACT FROM AUTHOR]