Declines in the abundance of long-lived and habitat-forming species on continental shelves have attracted particular attention given their importance to ecosystem structure and function of marine habitats. The study of undisturbed habitats defined as “pristine areas” is essential in creating a frame of reference for natural habitats free of human interference. Gorgonian species are one of the key structure-forming taxa in benthic communities on the Antarctic continental shelf. Current knowledge of the diversity, distribution and demography of this group is relatively limited in Antarctica. To overcome this lack of information we present original data on pristine and remote populations of gorgonians from the Weddell Sea, some of which display the largest colony sizes ever recorded in Antarctica. We assessed the distribution patterns of seven gorgonian species, a morphogroup and a family in front of the Filchner Ronne Ice Shelf (Weddell Sea) by means of quantitative analysis of video transects. Analysis of these videos showed a total of 3140 colonies of gorgonians with the highest abundance in the southern section and a significantly clumped distribution. This study contributes to the general knowledge of pristine areas of the continental shelf and identifies the eastern Weddell Sea as a hotspot for habitat-forming species.

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SUMMARY: The taxonomy of the primnoid genus Amphilaphis Studer and Wright in Studer, 1887 has been in a confused state for a long time and a revision of the species included in that genus has become a necessity. We have revised and redescribed the species previously included in the genus using up-to-date technology, such as polyp and sclerite images obtained with scanning electron microscopy (SEM). As a result of this study, because the type species of Amphilaphis is actually a Thouarella species, we consider the genus Amphilaphis to be no longer valid. One of the species previously considered in Amphilaphis has a set of morphological characters that are not recognizable in any of the current primnoid genera. Primnocapsa n. gen. has a dichotomous branching pattern, polyps placed singly, in spirals around the branchlets, 8 opercular scales with the inner surface keeled and with 2 mounds basally and 8 marginal scales offset from the operculars. The new genus is described and illustrated. Moreover, one of the re-examined species has been included in a new subgenus, Faxiella n. subgen. of Plumarella Gray, 1870 because it has polyps placed in pairs. Finally, the remaining re-examined species have been included in the genus Thouarella Gray, 1870, one of the most specious primnoid genera.Keywords: Cnidaria, new genus, new subgenus, Faxiella, Primnocapsa, Thouarella.RESUMEN: Revisión y redescripción de las especies incluidas previamente en el género AmphilAphis Studer y Wright en Studer, 1887 (Octocorallia: Primnoidae). -Durante mucho tiempo, el género de primnoido Amphilaphis Studer y Wright en Studer, 1887, ha sido un cajón de sastre y la revisión de las especies incluidas en este género se ha convertido en algo indispensable. Mediante el uso de la tecnología más actual, como es la microscopía electrónica de barrido (SEM), para la obtención de imágenes de pólipos y escleritos, hemos revisado y redescrito todas las especies previamente incluidas en el género. Como resultado de este estudio, y dado que la especie tipo de Amphilaphis es de hecho una especie perteneciente al género Thouarella, concluimos que el género Amphilaphis no debería considerarse válido. Una de las especies previamente consideradas en este género presenta un conjunto de caracteres morfológicos no reconocibles en ningún género de primnoido. Primnocapsa n. gen. se caracteriza por tener un patrón de ramificación dicotómico, pólipos aislados dispuestos en espiral alrededor de las ramas, ocho escamas operculares con quilla y con dos protuberancias basales y ocho escamas marginales dispuestas de forma alterna con las operculares. El nuevo género es descrito e ilustrado. Además, una de las especies re-examinadas ha sido incluida en un nuevo subgénero, Faxiella n. subgen. de Plumarella Gray, 1870 por poseer pólipos dispuestos en pares. Por último, las restantes especies re-examinadas han sido incluidas en el género Thouarella Gray, 1870, uno de los géneros de primnoidos con más especies.