Poliquetos de fondos blandos en el Estrecho de Magallanes capturados durante la campaña oceanográfica italiana en febrero-marzo de 1991

Species composition, distribution and biogeography of polychaetes collected from the soft bottoms of the Straits of Magellan (South America) in February-March 1991 are reported. In 16 benthic samples, collected with different tools (Charcot and triangular dredges, van Veen grab), a total of 1132 individuals belonging to 119 taxa of polychaetes were collected; only 49 of the taxa found have been determined at species level. Eighteen species were recorded for the first time in the Straits of Magellan. Species richness was relatively high considering both the number of individuals collected, and the taxa known from previous studies on the area (182 species). The biogeographical analysis, conducted only on the 49 taxa classified at the species level, showed the dominance of Magellan-Antarctic-Subantarctic species (M-An-S 50%), followed by Magellan-American (M-Am 14%), Magellan-Antarctic (M-An 12%), Magellan-Subantarctic (M-S 6%), Cosmopolitans (C 10%), and also by a few species with disjunct distribution (D 8%). Values of the Sørensen similarity index among stations were very low (below 0.30) with a few exceptions. Both number of species and of individuals were higher in the Atlantic sector of the Straits, especially at some stations characterized by heterogeneous mixed sediments (gravels and pebbles) and biogenic debris (mollusc thanatocoenosis). The high number of species recorded, coupled with low similarity values among stations, suggests that the soft bottoms of the Straits of Magellan show, at medium scale, a highly diversified mosaic of different biotopes. This can be due to various factors which are expected to vary along the wide geographic area investigated, such as the wide bathymetric range sampled, the type of sampling gears used, and last but not least the occurrence of many different environmental situations along the Straits.En el presente trabajo se describen composición específica, distribución y biogeografía de los poliquetos recolectados en los fondos blandos del Estrecho de Magallanes (Sudamérica), durante los meses de febrero y marzo del año 1991. En 16 muestras bentónicas, recogidas con diferentes métodos (dragas Charcot, triangular y van Veen), se encontraron un total de 1132 individuos pertenecientes a 119 taxones de poliquetos. De éstos tan solo 49 han sido determinados a nivel de especie y a su vez 18 han resultado ser nuevas citas para el Estrecho de Magallanes. La riqueza específica encontrada fue relativamente alta, considerando tanto el número de individuos recolectados como los taxones conocidos gracias a estudios previos en el área (182 especies). El análisis biogeográfico, efectuado solamente sobre los taxones clasificados a nivel de especie (49), ha demostrado la dominancia de especies Magallano-Antártico- Subantárticas (M-An-S 50%), seguida por especies Magallano-Americanas (M-Am 14%), Magallano-Antárticas (M-An 12%), Magallano-Subantárticas (M-S 6%), Cosmopolitas (C 10%) y también por especies de distribución disjunta (D 8%). Los valores del índice de similaridad de Sørensen entre estaciones fueron muy bajos (inferiores a 0.3) salvo algunas excepciones. Tanto el número de especies como el número de individuos fueron más elevados en el sector atlántico del Estrecho, particularmente en algunas estaciones caracterizadas por sedimentos heterogéneos de tipo mixto (gravas y guijarros), y restos biogénicos (tanatocenosis de moluscos). El elevado número de especies descrito, combinado con los valores bajos de similaridad entre estaciones, sugieren que los fondos blandos del Estrecho de Magallanes presentan, a media escala, un mosaico altamente diversificado de biotopos diferentes. Esto puede ser debido a varios factores que son responsables de la variación a lo largo de la vasta área geográfica investigada, tales como el amplio rango batimétrico estudiado, el tipo de instrumentación de muestreo, y en último lugar pero no menos destacable, la presencia de muchas situaciones ambientales diferentes a lo largo del Estrech

A Revision of the Deep-Sea Genus Axiokebuita Pocklington and Fournier, 1987 (Annelida: Scalibregmatidae)

[Abstract] The deep-sea genus Axiokebuita (Annelida, Scalibregmatidae) has hitherto been considered to contain two species, Axiokebuita minuta (Hartman, 1967) and Axiokebuita millsi Pocklington and Fournier, 1987, each rarely recorded in the literature and both supposedly having bipolar distributions. From the study of some types, other museum collection material, plus newly collected specimens from the slope depths of the Bellingshausen Sea and off the Antarctic Peninsula (Antarctica), Iceland and Iberian Peninsula, as well as from hydrothermal vents of the southeastern Pacific Ocean, the taxonomic history of the genus is revisited. Based on the results of this study, the features traditionally used to distinguish between the two species are actually the same in both. Therefore, A. millsi is proposed to be synonymised with A. minuta, which is redescribed and considered the only valid species of the genus, leaving Axiokebuita monotypic. Two previously unnoticed body sensory structures, i.e. a ciliated neck organ and a prostomial depression, were observed under scanning electron microscopy.United States. National Science Foundation; OCE- 0241613United States. National Science Foundation; OCE-0350554Ministerio de Educación y Ciencia; GLC2004–01856/AN