Magellanic Region Research Articles

Preliminary Assessment of Sea Star (Echinodermata, Asteroidea) Diversity in the Coastal Magellanic Region (South Chile) and Their Geographical Distribution

Sea stars are a diverse and important component of the Southern Ocean benthos. However, scarce information is available regarding their diversity, distribution, evolution, and taxonomic uncertainties persist for multiple taxa. The Magellanic Region (south of Chile) remains under-sampled despite its pivotal location for species distribution and diversity, being located at the crossroad of three ocean basins. In this study, we assessed the biodiversity of coastal Magellanic sea stars and their affinities with other oceanic bioregions. An integrative approach combining morphological identification with DNA barcoding was implemented to highlight taxonomic discrepancies such as suspected synonymy and unrecognised diversity. Firstly, we identified a total of 15 species from the coastal Magellanic Region and reported the occurrence of Cycethra frigida Koehler, 1917 for the first time in this region. The distribution of these 15 species ranged from only in South America to circumpolar, bipolar, or possibly cosmopolitan. Secondly, we highlighted possible synonymy in two species pairs within the genera Anasterias and Odontaster. This preliminary biodiversity assessment forms an important baseline for monitoring and conservation purposes, especially in the face of distribution shifts as a response to climate change and the increased presence of invasive species. Developmental mode has previously been suggested to be important in shaping biogeographical patterns. However, developmental mode was insufficient to explain the observed patterns, and other factors (e.g., physiological constraints, competition, bathymetrical range, and the possibility of passively rafting on kelp) are suggested to be at least equally important. Finally, an increase in barcoding effort is needed to better capture phylogeographic patterns for each species, both by increasing the number of specimens investigated and by covering a broader geographical range.

New insight into Cenozoic Orbitestellidae (Gastropoda: Heterobranchia) from the Magellanic Region based on lower Neogene and Recent species

AbstractPatagorbitestella new genus is here proposed to include two extant and one fossil species: P. ponderi (Linse, 2002) new combination, P. patagonica (Simone and Zelaya, 2004) new combination, and P. leonensis new species, the last described from the Punta Entrada Member of Monte León Formation (50°21′25.4”S, 68°53′05.9″W, Aquitanian to lower Burdigalian, lower Miocene). A protoconch sculptured with distinctive microscopic spiral threads serves as a per se diagnostic shell character for the new genus. Patagorbitestella n. gen. constitutes a distinctive lineage of orbitestellid gastropods inhabiting exclusively the Magellanic Region at least since the early Miocene. This is the first fossil record of Orbitestellidae in South America.UUID: http://zoobank.org/e48a4b73-1c0a-4bf7-aceb-8a180ef7e039

Populations of a New Morphotype of Corrugate Lessonia Bory in the Beagle Channel, Sub-Antarctic Magellanic Ecoregion: A Possible Case of On-Going Speciation

During a 2007 expedition dedicated to study kelp diversity within the Magellanic region, specimens of Lessonia Bory with corrugate, yellowish blades were found along the Beagle Channel. This type of corrugated Lessonia is uncommon, with exception of two species from New Zealand. Three possible hypotheses for its origin were explored in this study: an introduction of L. adamsiae Hay or L. corrugata Lucas from New Zealand by trans-oceanic dispersal; a hybridization between Chilean Lessonia species and Macrocystis pyrifera C.Agardh, particularly abundant in the region; or the existence of a new, undescribed species. Except for their corrugate blades, the individuals displayed short cylindrical stipes, digitate holdfasts, abundant mucilage cavities in the cortex, and reproductive sori on the proximal part of the blades, all traits typical of the genus Lessonia. Molecular phylogenies based on mitochondrial (atp8-trnS spacer, cox1, cox3) and nuclear (ITS1) markers revealed that this corrugate form of Lessonia is neither the result of hybridization with Macrocystis C.Agardh nor an introduction of Australasian corrugate species, L. corrugata or L. adamsiae, but has a close affinity with L. flavicans Bory. Field prospection in five sites along the Beagle Channel indicated that the species occurs in shallow depth (4-6 m), as dense populations of 100% of corrugated individuals, never intermixed with populations of L. flavicans. The possibility of an incipient speciation process in the region is discussed.

A Subantarctic rare gastropod reveals a new type of spawn among heterobranchs

Abstract Spawn and specimens of Toledonia biplicata comb. nov. were collected from Burdwood Bank during March 2013. Species-level identification was derived from radular, shell and spawn characters. A low number of eggs laid per spawn (one to three), absence of an external gelatinous mass and a considerably thickened capsule wall (~50 µm) constitute a unique combination of spawn characters among heterobranchs. Egg capsules are ovoid in shape and measure 600–763 × 450–656 µm. They are filled with albuminous liquid, allowing complete intracapsular development of a single embryo. The developmental stages recognized are uncleaved eggs (153 µm in average diameter), veliger stages (279–378 µm in maximal length) and prehatchling juveniles (442–609 µm). Toledonia biplicata increases its volume 40-fold during its intracapsular development, whereas other comparable cephalaspids increase ≤ 4-fold. The role of the capsule wall as protection and an additional source of food is discussed. The adaptive value of these characters in relationship to the environmental conditions of the Magellanic region is discussed. A comparison with the spawn of other cephalaspids, nudibranchs and pleurobranchids is conducted, and the taxonomic implications are discussed. This is the first description of the spawn and developmental stages of a representative of the genus Toledonia.

Two new species of Psolus Oken from Brazil (Holothuroidea: Psolidae),with neotype designation and redescription of Psolus vitoriae Tommasi, 1971, and a key to the southwestern Atlantic and Magellanic species.

The taxonomy of the southeastern Brazilian species of Psolus is reviewed and two new species described. Additionally, P. vitoriae is redescribed based on a newly designated neotype and supplemental material from the type locality and nearby regions. The synonymy of P. marcusi with P. patagonicus is called into question. The calcareous ring is useful for distinguishing between some Psolus species. Psolus tommasi sp. nov. is characterized by having five oral valves, an anus covered by a variable number of small, irregular anal valves, oral and anal valves distinct from body wall scales, calcareous ring interradial plates entire, calcareous ring simple, without posterior processes; radial and interradial plates entire, dorsal ossicles spheroid bodies and sole ossicles knobbed and smooth perforated plates. Psolus thandari sp. nov. is characterized by granules on body scales; mouth surrounded by five to seven triangular valves of equal size; anus surrounded by a variable number of small and irregular anal valves that grade into surrounding scales; calcareous ring with interradial plates entire. Six species of Psolus are known from the southwestern Atlantic and Magellanic region: P. vitoriae (São Paulo, Brazil); P. patagonicus (Mar del Plata to Tierra del Fuego, Argentina; Strait of Magellan and Cape Horn); P. segregatus (Patagonia, Argentina; Strait of Magellan, Chile; Hikurangi Margin and Chatham Rise, New Zealand); P. antarcticus (Magellanic region; South Georgia Island, southern Atlantic Ocean; Macquarie Island and Ridge, New Zealand); P. lawrencei (Mar del Plata, Argentina) and Psolus murrayi Théel, 1886 (Montevideo, Uruguay). A key to the species of Psolus from the southwestern Atlantic and Magellanic region, and a synoptic table to all southern Atlantic Psolus species is provided.

The Antarctic Circumpolar Current isolates and connects: Structured circumpolarity in the sea star Glabraster antarctica.

AimThe Antarctic Circumpolar Current (ACC) connects benthic populations by transporting larvae around the continent, but also isolates faunas north and south of the Antarctic Convergence. We test circumpolar panmixia and dispersal across the Antarctic Convergence barrier in the benthic sea star Glabraster antarctica.LocationThe Southern Ocean and south Atlantic Ocean, with comprehensive sampling including the Magellanic region, Scotia Arc, Antarctic Peninsula, Ross Sea, and East Antarctica.MethodsThe cytochrome c oxidase subunit I (COI) gene (n = 285) and the internal transcribed spacer region 2 (ITS2; n = 33) were sequenced. We calculated haplotype networks for each genetic marker and estimated population connectivity and the geographic distribution of genetic structure using ΦST for COI data.Results Glabraster antarctica is a single circum‐Antarctic species with instances of gene flow between distant locations. Despite the homogenizing potential of the ACC, population structure is high (ΦST = 0.5236), and some subpopulations are genetically isolated. Genetic breaks in the Magellanic region do not align with the Antarctic Convergence, in contrast with prior studies. Connectivity patterns in East Antarctic sites are not uniform, with some regional isolation and some surprising affinities to the distant Magellanic and Scotia Arc regions.Main conclusionsDespite gene flow over extraordinary distances, there is strong phylogeographic structuring and genetic barriers evident between geographically proximate regions (e.g., Shag Rocks and South Georgia). Circumpolar panmixia is rejected, although some subpopulations show a circumpolar distribution. Stepping‐stone dispersal occurs within the Scotia Arc but does not appear to facilitate connectivity across the Antarctic Convergence. The patterns of genetic connectivity in Antarctica are complex and should be considered in protected area planning for Antarctica.

A revision of the genus Savatieria Rochebrune & Mabille, 1885: an endemic group of buccinulid gastropods from the Magellanic region

Fil: Di Luca, Javier Agustin. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; Argentina

A new deep water gastropod of the genus Parabuccinum (Neogastropoda: Buccinulidae) from southwestern Atlantic waters with new data on the distribution of all species

A new species of the buccinulid genus Parabuccinum Harasewych, Kantor, and Linse, 2000 is described from Southwestern Atlantic deep waters (~54°S, 60°W). Parabuccinum politum sp. n. differs from all other species in the genus in having a smooth shell. Radula, operculum, and soft parts match the other species of the genus. New data on the distribution of all the species of Parabuccinum extends the range of the genus to 37°S in deep waters of the SW Atlantic. Based on present data, only P. bisculptum and P. raucherti were collected outside the Magellanic region to which all the remaining species are confined.

Taxonomic status of some species of Aspidostomatidae (Bryozoa, Cheilostomata) from the Oligocene and Miocene of Patagonia (Argentina)

AbstractThe bryozoan genusAspidostomaHincks, 1881 has been regarded as the only representative of the Aspidostomatidae Jullien, 1888 in Argentina to date. Its type species,Aspidostoma giganteum(Busk, 1854), is presently distributed in the Magellanic Region (Argentina and Chile) and has been recorded in Oligocene and Miocene fossil deposits of Santa Cruz and Chubut, respectively. New material from San Julián (late Oligocene), Monte León (early Miocene), Chenque (early to middle Miocene), and Puerto Madryn (late Miocene) formations suggests, however, thatA. giganteumis not represented in the fossil record. Material from Puerto Madryn Formation previously regarded asA. giganteumis here recognized asAspidostoma roveretoinew species.Aspidostoma ortmanniCanu, 1904 is revalidated for the species from the San Julián Formation.Aspidostoma armatumnew species andAspidostoma tehuelchenew species are introduced for material from the Monte León and Chenque formations, respectively.Aspidostoma incrustansCanu, 1908, from the early Miocene, is redescribed.MelychocellaGordon and Taylor, 1999, which differs fromAspidostomain having vicarious avicularia and lacking a median ridge and a quadrangular process proximal to the opesia-orifice, is so far represented by three Paleogene species from the Chatham Islands (Southwest Pacific). The material from Monte León allowed us to transferAspidostoma flammulumCanu, 1908 toMelychocella, resulting in the new combinationMelychocella flammula(Canu, 1908).Melychocella biperforatanew species is described from the lower Miocene Monte León and Chenque formations. The presence ofMelychocellain the Neogene of Patagonia extends its geographic distribution and its temporal range.UUID:http://zoobank.org/d84df2d8-cab2-4e74-82b8-7c67d938a58f

Revision of the genera Pareuthria Strebel, 1905, Glypteuthria Strebel, 1905 and Meteuthria Thiele, 1912 (Gastropoda: Buccinulidae) with the description of three new genera and two new species from Southwestern Atlantic waters.

This revision of the buccinulid genera Pareuthria Strebel, 1905, Glypteuthria Strebel, 1905 and Meteuthria Thiele, 1912 includes all the reported nominal species and type specimens. A total of 13 valid species included in six genera are described and illustrated. All but one -P. fuscata- live in shallow waters around the Magellanic region and even reach lower latitudes including deeper waters off the Buenos Aires province. The genus Pareuthria includes P. fuscata (Bruguière, 1789), P. atrata (E. A. Smith, 1881) for which a lectotype is designated, and P. venustula Powell, 1951. P. fuscata is also confirmed to occur in New Zealand waters. Glypteuthria Strebel, 1905 includes only the type species G. meridionalis (E.A. Smith, 1881). Two species are included in the genus Meteuthria Thiele, 1912, the type species M. martensi (Strebel, 1905), for which a lectotype is designated, and M. batialis n. sp., which is described herein based on specimens from deep water off Buenos Aires province. Three new genera are described: Falsimacme n. gen. to include only the type species F. kobelti (Strebel, 1905) (formerly in the genus Meteuthria); Argeneuthria n. gen. to include A. cerealis (Rochebrune & Mabille, 1885), A. paessleri (Strebel, 1905), A. euthrioides (Melvill & Standen, 1898), A. philippii (Strebel, 1905) and A. varicosa new species; and Microdeuthria n. gen. to include only M. michaelseni (Strebel, 1905). In addition, "Anomacme" multituberculata Castellanos, Rolán & Bartolotta, 1987 included by Dell (1990) in Meteuthria is excluded from the latter genus based on the morphology of the radula.

Sea cucumbers of the Kerguelen Plateau, with descriptions of new genus and species (Echinodermata: Holothuroidea)

A new genus of holothuroid, Calcamariina O Loughlin, and five new species of holothuroids, with authors O Loughlin & Skarbnik-Lopez, from near Heard and McDonald Islands on the Kerguelen Plateau in the Southern Ocean are described: Calcamariina hibberdi, Calcamariina moorea, Echinocucumis ampla, Psolus heardi, Paracaudina championi. The new species Paracaudina championi has the diagnostic characters of both Paracaudina Heding and Hedingia Deichmann. Molpadia violacea Studer is raised out of synonymy with Molpadia musculus Risso. Molpadia violacea is reviewed, and an extended distribution around Antarctica is proposed. The distribution of Molpadia magdae O Loughlin (in O Loughlin et al.) is extended from the South Shetland Islands to Prydz Bay. Pseudopsolus macquariensis forma gruai Cherbonnier & Guille is raised to species status. Laevocnus O Loughlin (in O Loughlin et al.) is an objective junior synonym of Pentactella Verrill. A sensu stricto diagnosis is provided for Pentactella. The always smaller, brood-protecting Psolus ephippifer Thomson specimens may be juveniles of the sympatric and always larger, non-brooding, Psolus paradubiosus Carriol & Feral specimens. Comprehensive lists are provided for all holothuroids that have been reported from the vicinity of Heard and McDonald Islands, and for the Kerguelen Plateau. Individual lists are provided for all holothuroid specimens from the vicinity of Heard and McDonald Islands that are held in Museum Victoria, the South Australian Museum, and the Tasmanian Museum and Art Gallery. Holothuroid species variably common to the Kerguelen Plateau, coast of Antarctica, Macquarie Island, Magellanic Region and Bouvetoya Island are listed.

The evolution of seabirds in the Humboldt Current: new clues from the Pliocene of Central Chile.

BackgroundDuring the last decade, new Neogene fossil assemblages from South America have revealed important clues about the evolution of seabird faunas in one of the major upwelling systems of the world: the Humboldt Current. However, most of this record comes from arid Northern Chile and Southern Peru and, in consequence, our knowledge of the evolutionary history of seabirds in the temperate transitional zone is negligible. A new Late Pliocene assemblage of fossil birds from the coastal locality of Horcon in Central Chile offers a unique opportunity to fill this gap.Principal FindingsIsolated bones of a medium-sized penguin are the most abundant bird remains. Morphological and cladistic analyses reveal that these specimens represent a new species of crested penguin, Eudyptes calauina sp. nov. Eudyptes is a penguin genus that inhabit temperate and subantarctic regions and currently absent in central Chile. Additionally, a partial skeleton of a small species of cormorant and a partial tarsometatarsus of a sooty shearwater have been identified.Conclusion/SignificanceThe Horcon fossils suggest the existence of a mixed avifauna in central Chile during the Pliocene in concordance with the latitudinal thermal gradient. This resembles the current assemblages from the transitional zone, with the presence of species shared with Northern Chile and Southern Peru and a previously unrecorded penguin currently absent from the Humboldt System but present in the Magellanic region. Comparison of Pliocene seabird diversity across the Pacific coast of South America shows that the Horcon avifauna represents a distinctive assemblage linking the living faunas with the Late Miocene ones. A comparison with the fossil record near the Benguela Current (west coast of southern Africa) suggests that the thermic gradient could play an important role in the preservation of a higher diversity of cold/temperate seabirds in the Humboldt Current.

El estrecho de Magallanes como antesala del Pacífico: evolución cartográfica y toponimia entre los siglos XVI y comienzos del XVIII

The Strait of Magellan was one of the geographical areas which generated more attention in the cartographers during the XVI and XVII centuries. In fact, for the Chilean case, together with Chiloe and Valdivia, the Magellanic region is the most represented. The reasons are both navigational and strategic purposes. That means that the surviving examples on public and private archives of several countries are comparatively abundant. The present study shows a new piece, which forms part of a navigational chart or «Derrotero» that is conserved in the Historical Archive of the Peruvian Navy, whose dating is roughly the early XVII century, although showing geographical representations from the previous century.

Growth responses to temperature, salinity and nutrient variations, and biomass variation and phenology of Ahnfeltia plicata (Rhodophyta, Ahnfeltiales): a commercially interesting agarophyte from the Magellanic Region, Chile

Ahnfeltia plicata (Hudson) E.M. Fries (Rhodophyta, Ahnfeltiales) is one of the most commercially important agarophytes in the world for its production of agar that is high quality and low in sulfate content. In the Magellanic Region, A. plicata forms extensive beds with high biomass production, which could be commercially exploited for agar production. The purposes of this study were to determine the optimal conditions of temperature, salinity, and culture medium; to evaluate the effects of different types and concentrations of auxins and cytokinins on growth of red and yellow gameto- phytes; and to provide background information on ecological parameters of natural population of A. plicata .T emperatures of 5, 8, 15, and 23 °C were tested, and the interaction of salinity of 25 and 35 psu with Provasoli enriched medium in half (PES/2) and quarter strength (PES/4), and with von Stosch enriched medium in half (VSES/2) and quarter strength (VSES/4) was also conducted. Concentrations of 5.0 and 50.0 μ Mo f two auxins (indole-3-acetic acid (IAA), 2,4-dichlorophenoxyacetic acid (2,4-D)), and two cytokinins (isopentenyladenine (iP) and benzylaminopurine) were added to VSES medium and gelled with 0.5 % agar. Each treatment was tested with three replicates. Red gametophytes of A. plicata tolerate a range of temperature variation, from 5 to 23 °C, and the optimum temperature for growth was 15 °C. The highest growth rate was observed in salinity of 35 psu with half strength of von Stosch culture medium. Red and yellow gametophytes showed different re- sponses to plant growth regulators, and red gametophytes were more sensitive than yellow ones to the addition of IAA and high concentration of iP. However, growth of red gametophytes of A. plicata was stimulated by 2,4-D. The differential sensitivity of red and yellow gametophytes to plant growth regulators sug- gests the need to test other types and concentrations of auxins and cytokinins.

Two new species and a new genus of Calloporidae (Bryozoa: Cheilostomata) from the Southwest Atlantic

The family Calloporidae occupies a basal position in the classification of the Cheilostomata, the relatively simple calloporid morphology seeming to be the basic pattern for the adaptive radiation of cheilostome bryozoans. The ovicells of the Calloporidae may be formed by the maternal zooid or the distal zooid, which can be an autozooid, a vicarious avicularium or a kenozooid. Examination of new calloporid material from the southern Patagonian shelf revealed the existence of two new species and a new genus. Kenoaplousinafissurata gen. nov., sp. nov. is characterized by its distinctive kenozooidal ooecium. The new genus is also deemed to include Aplousina grandipora Moyano, an allied species from the Chilean continental slope. Alderina simplicissima sp. nov., is also described from the Magellanic region.

ECHINODERMS AS CLUES TO ANTARCTIC ~ SOUTH AMERICAN CONNECTIVITY

table.MsoNormalTable { font-size: 10pt; font-family: Arial,sans-serif; } I solation and climate change has lead to an Antarctic marine biota rich in endemic taxa. But evidence exists for the occurrence of several shared marine species between the Southern Ocean and other basins. This manuscript reviews on the echinoderm taxa known from the Antarctic and South America, and evaluates some evidences for the connectivity between these continents. Metadata from several studies and data from the Brazilian continental margin were used for the analyses. A total of 602 echinoderm species have been recorded so far at both regions, 82 of those (~14 %) are shared between Antarctica and South America, and from these around 46 % are typically deep-sea ones. A high species richness was found at the Antarctica Peninsula, South Shetland Is. and South Georgia, possibly resultant from highest sampling effort at these regions. Distinct geological history and the tectonic activities play an important role in regulating the benthic faunal assemblage of these regions. A overlap was found between the echinoderm fauna from the South American cone, and mainly the regions around the Antarctic Peninsula. The echinoderm fauna from the Brazilian margin distinguished from those at the tip of the continent, although a few shared taxa occurred. A species assemblage turnover was identified from the Uruguayan margin. Also, the whole Magellanic region showed more affinities with the Argentinean Atlantic margin and the Falkland/Malvinas Is. than the southern Pacific Chilean margin. South Georgia, as transition between the South American and Antarctic regions, shared species with both continents. The considerably low ratio between the number of shared and total species records from the Antarctic regions revealed that most species are most likely endemic to the Southern Ocean. But future explorations of the South American and Antarctic deep sea margins and basins could reveal a higher number of shared echinoderm species than that reported here. All these comparisons should be backed up by taxonomic calibration and use of molecular tools in order to distinguish cryptic species and evaluate genetic populations' structure, as these would lead to a better understanding of observed biogeographical patterns.

Molecular phylogeny and historical biogeography of Nacella (Patellogastropoda: Nacellidae) in the Southern Ocean

The evolution and the historical biogeography of the Southern Ocean marine benthic fauna are closely related to major tectonic and climatic changes that occurred in this region during the last 55 million years (Ma). Several families, genera and even species of marine organisms are shared between distant biogeographic provinces in this region. This pattern of distribution in marine benthic invertebrates has been commonly explained by vicariant speciation due to plate tectonics. However, recent molecular studies have provided new evidence for long-distance dispersion as a plausible explanation of biogeographical patterns in the Southern Ocean. True limpets of the genus Nacella are currently distributed in different biogeographic regions of the Southern Ocean such as Antarctica, Kerguelen Province, southern New Zealand Antipodean Province, North-Central Chile and South American Magellanic Province. Here, we present phylogenetic reconstructions using two mitochondrial DNA markers (Cytochrome Oxidase I and Cytochrome b) to look into the relationships among Nacella species and to determine the origin and diversification of the genus. Phylogenies were reconstructed using two methods, Maximum Parsimony and Bayesian Inference, while divergence time among Nacella species was estimated following a relaxed Bayesian approach. For this purpose, we collected inter- and subtidal species belonging to four biogeographic regions in the Southern Ocean: Antarctica, Kerguelen Province, Central Chile, and Magellanic Province. Our molecular results agree with previous morphological and molecular studies supporting the monophyly of Nacella and its sister relationship with Cellana. Two rounds of diversification are recognized in the evolution of Nacella. The first one occurred at the end of the Miocene and gave rise to the main lineages, currently distributed in Antarctica, South America or Kerguelen Province. Large genetic divergence was detected among Nacella species from these distant biogeographic provinces emphasizing the significance of trans-oceanic discontinuities and suggesting long-distance dispersal was relatively unimportant. The second diversification round consisted of a more recent Pleistocene radiation in the Magellanic region. In this province, different morphological species of Nacella exhibit extreme low levels of genetic divergence with absence of reciprocal monophyly among them. According to our time estimation, the origin and diversification of Nacella in the Southern Ocean is more recent (<15 MY) than the expected under the hypothesis of vicariant speciation due to plate tectonics. The evolution of this genus seems to be closely related to drastic climatic and oceanographic changes in the Southern Ocean during the middle-Miocene climatic transition. In spite of the high number of species described for the Magellanic Province, molecular results indicate that these species are the most derived ones in the evolution of the genus and therefore that the Magellanic region does not need to correspond to the origin center of Nacella. The absence of genetic divergence among these species supports a very recent radiation process accompanied by rapid morphological and ecological diversification.

Molecular Species Identification of Astrotoma agassizii from Planktonic Embryos: Further Evidence for a Cryptic Species Complex

The phrynophiurid brittle star Astrotoma agassizii is abundant in the cold temperate Magellanic region of South America and has a circumpolar Antarctic distribution. Three genetically distinct lineages were recently identified, with one in Antarctica geographically and genetically isolated from both South American lineages (Hunter R, Halanych KM. 2008. Evaluating connectivity in the brooding brittle star Astrotoma agassizii across the Drake Passage in the Southern Ocean. J Hered. 99:137-148.). Despite being an apparent brooding species, A. agassizii displayed a high genetic homogeneity at 2 mitochondrial markers (16s and COII) across a geographical range of more than 500 km along the Antarctic Peninsula. Here, using 16s ribosomal RNA sequences, we match a variety of early developmental stages (fertilized eggs, embryos; n = 12) collected from plankton samples in the Ross Sea to sequences of A. agassizii from the Antarctic Peninsula. The single 16s haplotype reported here is an identical match to one 16s haplotype found for A. agassizii from the Antarctic Peninsula, more than 5000 km away. Based on the regular occurrence of A. agassizii developmental stages in plankton samples, we propose that the Antarctic lineage of this species has a planktonic dispersive stage, with brooding restricted to the South American lineages. A different developmental mode would provide further evidence for cryptic speciation in this brittle star.

Stenothoe magellanica sp. n. (Crustacea, Amphipoda, Gammaridea, Stenothoidae) aus dem Magellangebiet von Südchile

Stenothoe magellanica sp. n. (Crustacea, Amphipoda, Gammaridea, Stenothoidae) from Magellanic South Chile. Gonzalez (1991) lists 6 representatives of the family Stenothoidae for the Chilean Magellanic region. These species belong to the genera Metopoides, Probolisca and Torometopa (syn.: Metopoides). During the “Victor Hensen Cruise, 1994” on some stations the new species Stenothoe magellanica could be found. Stenothoe magellanica sp. n. differs from the other 4 Stenothoe species which were found in the adjoining areas — in the region of the Subantarctic islands, in the Magellanic sub-region and in the Tristan da Cunha district. The “Victor Hensen Cruise” has been part of three recent campaigns in the Magellan area. The two other are the “Polarstern ANT XIII/4 Cruise 1996” and the “Vidal Gormaz CIMAR FIORD0 II Cruise 1996”. The objective of all the three cruises is to compare the faunal composition, the biogeographical and ecological traits of the benthic amphipod taxocoenoses from the Magellan region with the West and East Antarctic benthos.

Reproduction of Halicarcinus planatus (crustacea, decapoda, hymenosomatidae) in the Deseado River estuary, southwestern Atlantic Ocean

The small spider crab Halicarcinus planatus, is a common resident in the rocky coasts of the Magellanic region in South America. The H. planatus population in the Deseado River estuary differs from other populations of the same species in the spatial segregation of sexes. Between March 2002 and October 2003, samples were taken monthly from the lower intertidal and upper subtidal levels. All crabs captured were females. Additional samplings were carried out at the subtidal level to search for the presence of males. A total of 3,346 females were captured and their relative age was determined. Some of these females were maintained in the laboratory to study the terminal moult and the spawning seasons. The analysis of the ovary development of adolescents (ADO) and mature (MAT) females, and the times when females of different ages appear, when spermatophores are found inside spermathecae, and when post-spawning mortality takes place allowed us to establish the whole reproductive process. Adolescents are impregnated only once before the terminal moult. There are seven or eight spawnings after the moult, with a brief resting period between two successive reproductive seasons. The life span of mature females ranges between 15 and 22 months. Results indicate that the H. planatus population of the Deseado River estuary differs greatly from that of the Kerguelen Islands.