No abstract

The colonial ascidian Synoicum molle (Herdman, 1886) was recorded for the first time after its original description. The slope area where S. molle was discovered during the Challenger Expedition (1872-1876), located at the mouth off Río de La Plata (Argentine Sea), still remains highly underexplored. During a series of deep-sea prospections along the SW Atlantic (A.R.A. Puerto Deseado, August 2012), 7 colonies of S. molle were collected few km from the type locality. The finding permitted to perform, for the first time, a complete morphological description of this species. The proper identification of marine species, especially deep-sea organisms, has implications for the general knowledge of biodiversity, a necessary tool for the conservation and study of ecosystem benefits that marine environments provide.

The validity and size of the biogeographic Magellan Province of marine organisms have been the focus of discussion of many authors. The distribution of fish and other organisms has revealed a lack of homogeneity in the area, which has also been interpreted as comprising four different Provinces: Southern Chile (SCH), Tierra del Fuego (TDF), Southern Argentina (SAR), and the Malvinas/Falkland Islands (MAI). For the first time, we assess the ascidian fauna of this region to determine if the distribution of benthic sessile filter feeders corresponds to these biogeographic provinces. Ascidian species richness and percentages of endemism for these four areas were estimated using data from the literature and new sampling. Biogeographic affinities among SCH, TDF, SAR, and MAI were also calculated. The species Pyura pilosa, Molgula malvinensis, and Molgula manhattensis, the latter frequently considered as invasive, were found for the first time on the TDF shelf. The highest ascidian species richness was found in TDF (70 species), while the percentages of endemism greater than 10% (the minimum to qualify an area as a province) were found in TDF (15.7%) and SCH (11.1%). SAR and MAI showed the lowest percentages of endemism and the strongest affinity. Based on percentages of endemism, faunal affinities, and differences among the four provinces, we propose a separation of the South American Region into three Provinces: SCH, TDF, and SAR/MAI. Continued sampling of ascidians is considered to be particularly important, given the potential spread of invasive species throughout this region.

The morphology of corellids (Ascidiacea) has led to numerous misidentifications and wrong taxonomic decisions over the last century. Paradoxically, the morphology has also enabled new species to be identified and ancient entities to be re-established in the Southern Hemisphere. There are many examples of the integration of morphological and molecular data leading to the same taxonomic conclusions, and therefore we aimed to analyse DNA sequences of the gene cytochrome oxidase subunit I of currently accepted species within Corellidae occurring in the Southern Hemisphere. Haplotype networks along with phylogenetic trees and genetic distances not only corroborate the distinction between Corella eumyota and Corella antarctica, but also separate the latter into two potential groups, one located in Terre Adélie and the other in the Antarctic Peninsula (AP). Furthermore, the C. antarctica group from the AP was closely related to the allied abyssal species, Corynascidia suhmi from Terre Adélie. Although the number of new sequences is reduced, our results are congruent with a long record of suspicion on the matter and stress the need for deeper and more extensive investigation of this ascidian family.

The diversity of ascidians from the Southwestern Atlantic between 30°S and 40°S (southern Brazil, Uruguay and northern Argentina) remains as one of the poorest known of the West Atlantic. The objective of this work is to compile, analyze and discuss all published records of ascidians from Uruguay. They show the historical relevance of the studies performed by Herdman, Monniot F. and Monniot C. on ascidians collected at deep-sea stations by the HMS Challenger and the RV Atlantis II in the Argentine Basin. Total literature records include 38 ascidian species which are enumerated here for the first time. On the basis of the current knowledge, the ascidian fauna of Uruguayan waters encompasses: a) shallow-water species with temperate distribution (3 spp.); b) shelf and deep-sea species with Antarctic and Sub-Antarctic distribution (13 spp.); c) deep-sea species until now only collected off Río de La Plata (11 spp.); d) deep-sea species displaying a wide distribution (11 spp.). Only nine species have been recorded for the continental shelf; the remaining species were collected either from the slope (21) or the abyssal plain (5) or both deep-sea zones (3). Future research should be directed to record coastline and shelf species, assess the presence of exotic elements, and re-describe enigmatic species first described by Herdman (1882, 1886).

Deep-sea benthic communities from the Weddell Sea, Antarctica, were sampled in January–April 2005 in an area located between 61°S–70°S and 0°W–49°W. We found a total of eight ascidian species that belong to five different families, of which one corresponded to a new species. These were: Protoholozoa pedunculata Kott, 1969; Corynascidia suhmi Herdman, 1882; Styela andeepensis Maggioni & Tatián sp. nov.; Culeolus suhmi Herman, 1881; Culeolus anonymus Monniot F. & Monniot C., 1976; Culeolus likae Sanamyan K. & Sanamyan N., 2002; Oligotrema lyra (Monniot C. & Monniot F., 1973) and Asajirus indicus (Oka, 1913). We report: the extension of the known distribution ranges of P. pedunculata, Corynascidia suhmi, Culeolus suhmi, C. likae and A. indicus, being the first time they are collected from the Weddell Sea; and the shallowest record of C. likae. Six species were added to the list of ascidians of the Weddell Sea, being all deep-sea representatives. While the total number of ascidian species augmented from 43 to 49, the number of deep-sea representatives increased from 23 to 29. Our findings, thus, reinforce the need of performing more deep-sea prospections in the area.

The Southern Ocean is one of the most isolated marine ecosystems, characterized by high levels of endemism, diversity, and biomass. Ascidians are among the dominant groups in Antarctic benthic assemblages; thus, recording the evolutionary patterns of this group is crucial to improve our current understanding of the assembly of this polar ocean. We studied the genetic variation within Cnemidocarpa verrucosa sensu lato, one of the most widely distributed abundant and studied ascidian species in Antarctica. Using a mitochondrial and a nuclear gene (COI and 18S), the phylogeography of fifteen populations distributed along the West Antarctic Peninsula and Burdwood Bank/MPA Namuncurá (South American shelf) was characterized, where the distribution of the genetic distance suggested the existence of, at least, two species within nominal C. verrucosa . When reevaluating morphological traits to distinguish between genetically defined species, the presence of a basal disk in one of the genotypes could be a diagnostic morphological trait to differentiate the species. These results are surprising due to the large research that has been carried out with the conspicuous C. verrucosa with no differentiation between species. Furthermore, it provides important tools to distinguish species in the field and laboratory. But also, these results give new insights into patterns of differentiation between closely related species that are distributed in sympatry, where the permeability of species boundaries still needs to be well understood.

The understudied deep-sea benthic communities from the Southwestern Atlantic continental slope (200 m–3000 m depth) were sampled on August 2012 in an area located around 38°S that included the Mar del Plata submarine canyon. In these samplings we found a total of 16 ascidian species from six different families, of which two corresponded to new species. These were: Aplidium meridianum (Sluiter, 1906); Aplidium variabile (Herdman, 1886); Aplidium marplatensis Maggioni & Tatián (sp. nov. present work); Aplidium solitarium Maggioni & Tatián (sp. nov. present work); Synoicum georgianum Sluiter, 1932; Synoicum molle (Herdman, 1886); Synoicum sp.; Polysyncraton trivolutum (Millar, 1960); Sycozoa umbellata (Michaelsen, 1898); Ascidia meridionalis Herdman, 1880; Cnemidocarpa drygalskii (Hartmeyer, 1911); Styela squamosa Herdman, 1881; Pyura pilosa Monniot C. & Monniot F., 1974; Molgula pyriformis Herdman, 1881; Molgula setigera Ärnbäck-Christie-Linde, 1938 and Asajirus indicus (Oka, 1913). Based on morphological evidence, we propose the new synonymy: Molgula setigera Ärnbäck-Christie-Linde, 1938 = Molgula marioni Millar, 1960 = Molgula robini Monniot C. & Monniot F., 1983. We also propose to maintain Molgula pyriformis and Molgula malvinensis as separate species. We report: the extension of the distribution range of Aplidium meridianum, Synoicum georgianum, Polysyncraton trivolutum, Sycozoa umbellata, Cnemidocarpa drygalskii, Pyura pilosa and Molgula setigera, being the first time they are collected off La Plata River; the deepest registers for Synoicum georgianum, Poylsyncraton trivolutum, Sycozoa umbellata, Ascidia meridionalis, Pyura pilosa, Molgula pyriformis and Molgula setigera; and the shallowest register for Synoicum molle.