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How the near-shore marine benthic communities survived Quaternary glaciations in Antarctica is a major question for Southern Ocean biogeographers. Several hypotheses that consider life-history traits, such as bathymetric ranges and developmental modes, have been proposed. Nearshore species with high dispersive potential are expected to show star-like genealogies, with broadly distributed haplotypes surrounded by closely related variants at low frequencies, a consequence of rapid population post-glacial expansion mediated by larvae. By contrast, shallow-water taxa with low dispersal potential are expected to evidence marked genetic structure or even consist of separate cryptic species, due to their survival in small refugial populations subject to repeated bottlenecks. In this study we performed phylogeographic analyses on the high-latitude littorinid Laevilacunaria antarctica across its distribution from maritime Antarctica to South Georgia. This species is a highly abundant near-shore gastropod, commonly found on macroalgae, with low autonomous vagility and exhibits benthic protected development with no free-living dispersive stages. Such characteristics make this species a suitable model to test the above hypotheses. Contrary to low dispersal potential predictions, L. antarctica comprises a single unstructured unit across its distribution in maritime Antarctica, exhibiting a typical high-dispersal star-like, short-branched genealogy centered on a dominant broadly distributed haplotype. The South Georgia population, however, consists of a separate genetic unit, strongly differentiated from those of the maritime Antarctic. We estimate that these two genetic groups separated ~1.2 My, long before the Last Glacial Maximum and evolved independently in these areas. Our results thus provide partial support for the expected pattern for a near-shore marine benthic species with low innate dispersive potential. On a wider geographic scale (maritime Antarctica vs South Georgia), our results in L. antarctica provide support for the expected pattern for a near-shore marine benthic species with low innate dispersive potential. However, on a narrower scale (maritime Antarctica) life-history characters including the close association of the species with macroalgae, would allow dispersal and a species with low dispersal potential exhibits paradoxically an absence of genetic structure across hundreds of kilometers probably mediated by rafting. [ABSTRACT FROM AUTHOR]

Background The present dataset is a compilation of georeferenced occurrences of the littorinid genus Laevilacunaria Powell, 1951 (Mollusca, Gastropoda) in the Southern Ocean. Occurrence data were obtained from field expeditions (Antarctic and sub-Antarctic sampling) between 2015 and 2022, together with a review of published literature including records from 1887 to 2022. Three Laevilacunaria species have been recorded from the Southern Ocean: Laevilacunaria bennetti, L. antarctica and L. pumilio. New information The present dataset includes 75 occurrences, representing the most exhaustive database of this Antarctic and sub-Antarctic littorinid genus. The publication of this data paper was funded by the Belgian Science Policy Office (BELSPO, contract n°FR/36/AN1/AntaBIS) in the Framework of EU-Lifewatch as a contribution to the SCAR Antarctic biodiversity portal (biodiversity.aq). [ABSTRACT FROM AUTHOR]

Aim: The Antarctic Circumpolar Current imparts significant structure to the Southern Ocean biota. The Antarctic Polar Front is a major barrier to dispersal, with separate species (or sometimes intraspecific clades) normally occurring either side of this feature. We examined the biogeographic structure of an apparent exception to this rule in a widespread genus of the Southern Ocean, the periwinkle snail, Laevilitorina. Location: Southern Ocean. Taxon: Littorinidae, Laevilitorininae, Laevilitorina. Methods: Using 750 specimens from 16 Southern Ocean Laevilitorina populations across >8000 km, we analysed mitochondrial COI and nuclear 28S sequences to uncover the evolutionary history of these marine near‐shore snails. We utilized multi‐locus phylogenetic reconstructions, species‐delimitation analyses, divergence‐time estimations and geometric morphometrics. Results: Molecular data revealed that the widespread nominal species L. caliginosa comprises seven species‐level clades, all supported by morphological data, whereas the Antarctic nominal species L. antarctica, L. claviformis and L. umbilicata are conspecific. Six "caliginosa" clades are restricted to southern South America, but one lineage extends from Antarctica to distant sub‐Antarctic islands on both sides of the APF. Geometric morphometrics also identified significant differences among these clades, but uncoupled from genetic differentiation. Main conclusions: The apparent trans‐APF distribution of the poorly dispersing Laevilitorina caliginosa is largely illusory: this taxon consists of at least seven discrete species, only one of which has a trans‐APF distribution. Similar to most Laevilitorina species, the remaining six "caliginosa" clades are narrow endemics. Biogeographical patterns in Laevilitorina reflect the role of vicariance associated with geological processes together with recent long‐distance dispersal events. Laevilitorina originated near the Eocene/Oligocene boundary and diversified during the Miocene and the Pliocene. Laevilitorina is not a cryptic‐species complex: speciation was accompanied by hitherto unrecognized morphological differentiation. This study represents the most detailed molecular work on Southern‐Ocean littorinids and reveals unforeseen diversity across this globally important region. [ABSTRACT FROM AUTHOR]

Hexacorals are important components of macrobenthic communities in the Southern Ocean, dominating Antarctic continental shelves. Most of the 119 sea anemones recorded for the Southern Ocean are endemic (81% and 25% endemic species and genera, respectively, one endemic family) with only two species extending beyond the limits of the Southern Ocean. Over 70% of the 83 genera in the Southern Ocean are monotypic, including half of the generic diversity in superfamily Actinostoloidea, which suggests that Antarctica has been isolated long enough for the evolution of new genera but not for many families to evolve. Here, we describe Chitinactis marmara gen. & sp. nov. , a new monotypic actinostoloidean genus from Antarctica diagnosed by its unique bi-layered cuticle on column, hexamerous symmetry, unequal development of younger mesenteries and mesogleal tentacle musculature. We also re-describe and extend the geographic distribution of Scytophorus striatus , another endemic Antarctic species. Based on morphological and molecular data, we establish the phylogenetic position of C. marmara and discuss the implications of the phylogenetic position of S. striatus for the resurrection and circumscription of the family Halcampoididae and the evolution of burrowing sea anemones. Finally, we discuss evidence for an actinostoloidean deep-sea, polar lineage of burrowing sea anemones. [ABSTRACT FROM AUTHOR]

Specimens of Pycogonida belonging to the genus Ammothea collected during the Polarstern ANT-XXIX/3 cruise (January 22-March 18, 2013), to Bransfield Strait and Eastern Weddell Sea, were studied. Eight species are recognized in this collection: Ammothea bicorniculata, A. calmani, A. carolinensis, A. clausi, A. minor, A. nadiae n. sp., A. spinosa, and A. striata. Morphological variability is discussed. The bathymetric range of A. bicorniculata and A. minor is enlarged and A. bicorniculata is reported for only the second time. Ammothea nadiae n. sp. is described and compared with its closest congeners. An updated key to species is presented. [ABSTRACT FROM AUTHOR]

Mysella narchii sp. nov. is described from the material collected in shallow-waters of Admiralty Bay at King George Island, South Shetlands, Antarctica. The species is characterized by shell features, biology and functional anatomy. The main shell features distinguishing M. narchii sp. nov. from all other Antarctic, Subantarctic and Magellanic Mysella spp. are provided, as are anatomical characteristics that separate this new species from M. charcoti (Lamy, 1906), its most similar congener and the first Antarctic species studied in its morpho-functional aspects. M. narchii sp. nov. is an infaunal, free-living, predominantly deposit-feeding bivalve; its creeping sole and the secretion of byssal threads allow it to crawl vertically and live sporadically on firm substrata. [ABSTRACT FROM AUTHOR]

Eighty-seven samples containing isopods were studied from the Spanish programs “Bentart 94” and “Bentart 95” in the Livingston Island and nearby areas (South Shetlands, sub-Antarctic). The samples were obtained mainly using box corers (meiobenthos), an Agassiz dredge (epibenthos) and a suprabenthic sledge (suprabenthos). Seventy-eight species were found; 27 were recorded for the first time in the South Shetland Islands. Two other species (Austrosignum escandellaeandCoulmannia ramosae) had previously been described as new species from the specimens of the collection “Bentart 95”. The largest number of species were found at station number 6 (B95: 21 species). The largest populations were in sample 6TA (B95: 215 specimens ofParamunna rostrataand 99 specimens ofSantia mawsoni). As regards depth, the distribution of species varied from 2 m (Ceratoserolis trilobitoides, B95: sample 5TA) to 1,019 m (Ceratoserolis meridionalis, B95: sample A31 (5 mm)). Muddy bottoms were the most common habitat. The most diverse families were Munnopsidae (11 species), Paramunnidae (9 species) and Antarcturidae (9 species). This paper adds to our taxonomic and biogeographical knowledge of the benthic communities from the South Shetland Islands. [ABSTRACT FROM AUTHOR]

Two new species of Paramunnidae (Crustacea, Isopoda, Asellota) from the South Shetland Islands (sub-Antarctic) are described. Austrosignum escandellae sp. nov. has long eyestalks, dorsum slightly sculpted (transverse bumps on pereonites 1-5), and lateral margins of pereonites rounded. The closest species is A. spinosum Kussakin, 1982 that also shows dorsum sculpted. The main differences are the ocular peduncle (short in A. spinosum) and the lateral margins of pereonites (pointed in A. spinosum). Coulmannia ramosae sp. nov. differs from the other two species of this genus (C. australis Hodgson, 1910 and C. frigida Hodgson, 1910) in that only the margins of pereonites 2-4 are expanded (into one point). A discussion of the Austrosignum/Munnogonium complex is provided with a comparative table of the species involved. [ABSTRACT FROM AUTHOR]