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Time calibrated phylogenies are typically reconstructed with fossil information but for soft‐bodied marine invertebrates that lack hard parts, a fossil record is lacking. In these cases, biogeographic calibrations or the rates of divergence for related taxa are often used. Although nudibranch phylogenies have advanced with the input of molecular data, no study has derived a divergence rate for this diverse group of invertebrates. Here, we use an updated closure date for the Isthmus of Panama (2.8 Ma) to derive the first divergence rates for chromodorid nudibranchs using multigene data from a geminate pair with broad phylogeographic sampling. Examining the species Chromolaichma sedna (Marcus & Marcus, 1967), we uncover deep divergences among eastern Pacific and western Atlantic clades and we erect a new species designation for the latter (Chromolaichma hemera sp. nov.). Next, we discover extensive phylogeographic structure within C. hemera sp. nov. sensu lato, thereby refuting the hypothesis of a recent introduction. Lastly, we derive divergence rates for mitochondrial and nuclear loci that exceed known rates for other gastropods and we highlight significant rate heterogeneity both among markers and taxa. Together, these findings improve understanding of nudibranch systematics and provide rates useful to apply to divergence scenarios in this diverse group. [ABSTRACT FROM AUTHOR]

The chromodorid nudibranch Goniobranchus aureopurpureus (Collingwood, 1881) is characterized by numerous yellow spots on a white mantle that is bordered with purple spots. It is believed to be widely distributed in both the Northern and Southern Hemispheres in the West Pacific, showing color varieties in a more-or-less geographically coherent manner. Chromodoris variata Risbec, 1928 (type locality: New Caledonia) has been considered a synonym. In addition, three, similar-looking congeners have been proposed as synonymous with G. aureopurpureus: G. albopustulosus (Pease, 1860) (type locality: Hawaii), G. alius (Rudman, 1987) (type locality: Tanzania), and G. rufomaculatus (Pease, 1871) (type locality: French Polynesia). To test the synonymies proposed above, we performed maximum-likelihood and Bayesian-inference analyses utilizing partial sequences of the cytochrome c oxidase subunit I (COI) and 16S rRNA genes. The taxon sampling included a specimen of G. aureopurpureus newly collected in Hokkaido, Japan, along with other sequences of Goniobranchus deposited in public databases (31 specimens representing 22 species), including one identified as 'Chromodoris aureopurpurea' from New South Wales, Australia; G. albopustulosus from Hawaii; and two 'Chromodoris rufomaculata' from Guam and the Mariana Islands. Goniobranchus aureopurpureus from Japan and from Australia were sister taxa in the resulting trees but differed from each other by 8.6% in terms of 658-bp COI, suggesting that these two represent closely-related but different biological entities. For the Australian taxon, Goniobranchus cf. variatus comb. nov. is proposed herein. Goniobranchus albopustulosus and G. rufomaculatus were not closely related to the G. aureopurpureus-G. cf. variatus clade, rejecting the hypothesis that they are synonymous with either of these species. However, G. albopustulosus and G. rufomaculatus appeared to comprise a single biological entity, warranting further investigation of this potential synonymy. The placement of the Indian Ocean G. alius also remains to be tested. [ABSTRACT FROM AUTHOR]

The marine-based West Antarctic Ice Sheet (WAIS) is considered vulnerable to irreversible collapse under future climate trajectories, and its tipping point may lie within the mitigated warming scenarios of 1.5° to 2°C of the United Nations Paris Agreement. Knowledge of ice loss during similarly warm past climates could resolve this uncertainty, including the Last Interglacial when global sea levels were 5 to 10 meters higher than today and global average temperatures were 0.5° to 1.5°C warmer than preindustrial levels. Using a panel of genome-wide, single-nucleotide polymorphisms of a circum-Antarctic octopus, we show persistent, historic signals of gene flow only possible with complete WAIS collapse. Our results provide the first empirical evidence that the tipping point of WAIS loss could be reached even under stringent climate mitigation scenarios. [ABSTRACT FROM AUTHOR]

An increasing number of Antarctic invertebrate taxa have been revealed as cryptic species complexes following DNA-based assessments. This ultimately necessitates a morphological reassessment to find traits that will help identify these cryptic or pseudocryptic species without the need for sequencing every individual. This work concerns comatulid crinoid echinoderms long considered to represent a single, circum-Antarctic species, Promachocrinus kerguelensis. The first molecular studies sought to distinguish the diversity in the complex and understand the constituent species distributions but stopped short of formal taxonomic assessment. Here, we continued to increase sample representation around the Southern Ocean and sequenced the mitochondrial COI gene for all new specimens, and additional genes for a few representatives. We also elucidated previously unappreciated features, particularly body pigmentation and morphology of the centrodorsal ossicle in an attempt to diagnose some species morphologically and based on DNA data. The species complex within Promachocrinus is here resolved into P. kerguelensis Carpenter, 1879, P. vanhoeffenianus Minckert, 1905, P. joubini Vaney, 1910, P. mawsoni (Clark, 1937) comb. nov. (transferred from Florometra) and four previously unnamed species, P. fragarius sp. nov., P. unruhi sp. nov., P. uskglassi sp. nov. and P. wattsorum sp. nov. Although most species can be distinguished morphologically, several cannot be reliably separated without DNA data. All sequenced species are essentially circum-Antarctic, with the notable exception of P. wattsorum sp. nov. that is restricted to the Prince Edward Islands in the sub-Antarctic Indian Ocean and P. vanhoeffenianus that is only known from the type locality in the Davis Sea. The vast nature of the Antarctic and Southern Ocean ecosystem dictates large scale sampling to understand the full extent of the biodiversity. ZooBank: urn:lsid:zoobank.org:pub:F871CDC8-973B-48CE-8A61-33658D4EB4B1 The Antarctic feather star Promachocrinus kerguelensis arguably comprises several species but taxonomic revision has not been attempted. Here we use DNA data and morphological characters to differentiate the species and formally described those that are new. The species complex was resolved into eight species, four of which are newly described, though not all can be reliably distinguished based on morphology. One of the new species has a restricted distribution, but the remainder appear to be circum-Antarctic. [ABSTRACT FROM AUTHOR]

Understanding the drivers of evolutionary innovation provides a crucial perspective of how evolutionary processes unfold across taxa and ecological systems. It has been hypothesised that the Southern Ocean provided ecological opportunities for novelty in the past. However, the drivers of innovation are challenging to pinpoint as the evolutionary genetics of Southern Ocean fauna are influenced by Quaternary glacial–interglacial cycles, oceanic currents and species ecology. Here we examined the genome‐wide single nucleotide polymorphisms of the Southern Ocean brittle stars Ophionotus victoriae (five arms, broadcaster) and O. hexactis (six arms, brooder). We found that O. victoriae and O. hexactis are closely‐related species with interspecific gene flow. During the late Pleistocene, O. victoriae likely persisted in a connected deep water refugium and in situ refugia on the Antarctic continental shelf and around Antarctic islands; O. hexactis persisted exclusively within in situ island refugia. Within O. victoriae, contemporary gene flow linking to the Antarctic Circumpolar Current, regional gyres and other local oceanographic regimes was observed. Gene flow connecting West and East Antarctic islands near the Polar Front was also detected in O. hexactis. A strong association was detected between outlier loci and salinity in O. hexactis. Both O. victoriae and O. hexactis are associated with genome‐wide increase in alleles at intermediate‐frequencies; the alleles associated with this peak appear to be species specific, and these intermediate‐frequency variants are far more excessive in O. hexactis. We hypothesise that the peak in alleles at intermediate frequencies could be related to adaptation in the recent past, linked to evolutionary innovations of increase in arm number and a switch to brooding from broadcasting, in O. hexactis. [ABSTRACT FROM AUTHOR]

The discovery of four new Xenoturbella species from deep waters of the eastern Pacific Ocean is reported here. The genus and two nominal species were described from the west coast [...]

Background: Common seadragons (Phyllopteryx taeniolatus, Syngnathidae) are an emblem of the diverse endemic fauna of Australia's southern rocky reefs, the newly recognized "Great Southern Reef." A lack of assessments spanning this global biodiversity hotspot in its entirety is currently hampering an understanding of the factors that have contributed to its diversity. The common seadragon has a wide range across Australia's entire temperate south and includes a geogenetic break over a former land bridge, which has called its status as a single species into question. As a popular aquarium display that sells for high prices, common seadragons are also vulnerable to illegal capture. Results: Here, we provide range-wide nuclear sequences (986 variable Ultraconserved Elements) for 198 individuals and mitochondrial genomes for 140 individuals to assess species status, identify genetic units and their diversity, and trace the source of two poached individuals. Using published data of the other two seadragon species, we found that lineages of common seadragons have diverged relatively recently (< 0.63 Ma). Within common seadragons, we found pronounced genetic structure, falling into three major groups in the western, central, and eastern parts of the range. While populations across the Bassian Isthmus were divergent, there is also evidence for secondary contact since the passage opened. We found a strong cline of genetic diversity from the range center tapering symmetrically towards the range peripheries. Based on their genetic similarities, the poached individuals were inferred to have originated from around Albany in southwestern Australia. Conclusions: We conclude that common seadragons constitute a single species with strong geographic structure but coherence through gene flow. The low genetic diversity on the east and west coasts is concerning given that these areas are projected to face fast climate change. Our results suggest that in addition to their life history, geological events and demographic expansions have all played a role in shaping populations in the temperate south. These insights are an important step towards understanding the historical determinants of the diversity of species endemic to the Great Southern Reef. [ABSTRACT FROM AUTHOR]

Anthropogenic climate change is causing observable changes in Antarctica and the Southern Ocean including increased air and ocean temperatures, glacial melt leading to sea‐level rise and a reduction in salinity, and changes to freshwater water availability on land. These changes impact local Antarctic ecosystems and the Earth's climate system. The Antarctic has experienced significant past environmental change, including cycles of glaciation over the Quaternary Period (the past ~2.6 million years). Understanding Antarctica's paleoecosystems, and the corresponding paleoenvironments and climates that have shaped them, provides insight into present day ecosystem change, and importantly, helps constrain model projections of future change. Biological archives such as extant moss beds and peat profiles, biological proxies in lake and marine sediments, vertebrate animal colonies, and extant terrestrial and benthic marine invertebrates, complement other Antarctic paleoclimate archives by recording the nature and rate of past ecological change, the paleoenvironmental drivers of that change, and constrain current ecosystem and climate models. These archives provide invaluable information about terrestrial ice‐free areas, a key location for Antarctic biodiversity, and the continental margin which is important for understanding ice sheet dynamics. Recent significant advances in analytical techniques (e.g., genomics, biogeochemical analyses) have led to new applications and greater power in elucidating the environmental records contained within biological archives. Paleoecological and paleoclimate discoveries derived from biological archives, and integration with existing data from other paleoclimate data sources, will significantly expand our understanding of past, present, and future ecological change, alongside climate change, in a unique, globally significant region. [ABSTRACT FROM AUTHOR]

Despite strong historical biogeographical links between benthic faunal assemblages of the Magellan region of South America and the Antarctic Peninsula, very few studies have documented contemporary movement and gene flow in or out of the Southern Ocean, especially across the Antarctic Polar Front (APF). In fact, oceanographic barriers such as the APF and Antarctica's long geologic isolation have substantially separated the continents and facilitated the evolution of endemic marine taxa found within the Antarctic region. The Southern Ocean benthic sea slug complex, Doris "kerguelenensis," are a group of direct‐developing, simultaneous hermaphrodites that lack a dispersive larval stage. To date, there are 59 highly divergent species known within this complex. Here, we provide evidence to show intraspecific genetic connectivity occurs across the APF for multiple species within the D. "kerguelenensis" nudibranch species complex. We addressed questions of genetic connectivity by examining the phylogeographic structure of the three best‐sampled D. "kerguelenensis" species and another three trans‐APF species using the protein coding mtDNA gene, cytochrome oxidase I. We also highlight alternative refugia uses among species with the same life history traits (i.e., benthic and direct developers) and for some species, extremely large distributions are established (e.g., circumpolarity). By improving our sampling of these nudibranchs, we gain better insight into the population structure and connectivity of the Antarctic region. This work also demonstrates how difficult it is to make generalizations across Antarctic marine species, even among ecologically‐similar, closely related species. [ABSTRACT FROM AUTHOR]

Chemical investigation of an Antarctic deep-water octocoral has led to the isolation of four new compounds, including three illudalane sesquiterpenoids (1–3) related to the alcyopterosins, a highly oxidized steroid, alcyosterone (5), and five known alcyopterosins (4, 6–9). The structures were established by extensive 1D and 2D NMR analyses, while 9 was verified by XRD. Alcyopterosins are unusual for their nitrate ester functionalization and have been characterized with cytotoxicity related to their DNA binding properties. Alcyopterosins V (3) and E (4) demonstrated single-digit micromolar activity against Clostridium difficile, an intestinal bacterium capable of causing severe diarrhea that is increasingly associated with drug resistance. Alcyosterone (5) and several alcyopterosins were similarly potent against the protist Leishmania donovani, the causative agent of leishmaniasis, a disfiguring disease that can be fatal if not treated. While the alcyopterosin family of sesquiterpenes is known for mild cytotoxicity, the observed activity against C. difficile and L. donovani is selective for the infectious agents. [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]

The Antarctic marine environment, although rich in life, is predicted to experience rapid and significant effects from climate change. Despite a revolution in the approaches used to document biodiversity, less than one percent of Antarctic marine invertebrates are represented by DNA barcodes and we are at risk of losing biodiversity before discovery. The ease of sequencing mitochondrial DNA barcodes has promoted this relatively 'universal' species identification system across most metazoan phyla and barcode datasets are currently readily used for exploring questions of species-level taxonomy. Here we present the most well-sampled phylogeny of the direct-developing, Southern Ocean nudibranch mollusc, Doris kerguelenensis to date. This study sampled over 1000 new Doris kerguelenensis specimens spanning the Southern Ocean and sequenced the mitochondrial COI gene. Results of a maximum likelihood phylogeny and multiple subsequent species delimitation analyses identified 27 new species in this complex (now 59 in total). Using rarefaction techniques, we infer more species are yet to be discovered. Some species were only collected from southern South America or the sub-Antarctic islands, while at least four species were found spanning the Polar Front. This is contrary to dispersal predictions for species without a larval stage such as Doris kerguelenensis. Our work demonstrates the value of increasing geographic scope in sampling and highlights what could be lost given the current global biodiversity crisis. [ABSTRACT FROM AUTHOR]

Five new alkaloids have been isolated from the lipophilic extract of the Antarctic tunicate Synoicum sp. Deep-sea specimens of Synoicum sp. were collected during a 2011 cruise of the R/V Nathanial B. Palmer to the southern Scotia Arc, Antarctica. Crude extracts from the invertebrates obtained during the cruise were screened in a zebrafish-based phenotypic assay. The Synoicum sp. extract induced embryonic dysmorphology characterized by axis truncation, leading to the isolation of aminopyrimidine substituted indolone (1–4) and indole (5–12) alkaloids. While the primary bioactivity tracked with previously reported meridianins A–G (5–11), further investigation resulted in the isolation and characterization of australindolones A–D (1–4) and the previously unreported meridianin H (12). [ABSTRACT FROM AUTHOR]

The sponge genus Sollasella has three named species, two from eastern Australia, (Queensland and New South Wales) and one from the western Arabian Sea. Using a combination of morphological and molecular data, we describe three new species from northern Western Australia. We sequenced Cytochrome Oxidase I and two different fragments of 28S to reconstruct genealogical relationships among species in the genus. Sollasella suttonorum sp. nov. is closest morphologically to the two previously known Australian species: S. digitata Lendenfeld, 1888 and S. moretonensis van Soest, Hooper, Beglinger and Erpenbeck 2006. However, S. ananas sp. nov., and S. maraca sp. nov. show a novel clubbed or oval (rather than digitate or lobed) morphology. These two species contain a unique spicule type (anatriaene-like) not previously reported in the Axinellida. As a consequence of this study the species diversity of Sollasella is doubled to six species, with all species confined to the Indian and Pacific oceans. [ABSTRACT FROM AUTHOR]

The drivers behind evolutionary innovations such as contrasting life histories and morphological change are central questions of evolutionary biology. However, the environmental and ecological contexts linked to evolutionary innovations are generally unclear. During the Pleistocene glacial cycles, grounded ice sheets expanded across the Southern Ocean continental shelf. Limited ice‐free areas remained, and fauna were isolated from other refugial populations. Survival in Southern Ocean refugia could present opportunities for ecological adaptation and evolutionary innovation. Here, we reconstructed the phylogeographic patterns of circum‐Antarctic brittle stars Ophionotus victoriae and O. hexactis with contrasting life histories (broadcasting vs brooding) and morphology (5 vs 6 arms). We examined the evolutionary relationship between the two species using cytochrome c oxidase subunit I (COI) data. COI data suggested that O. victoriae is a single species (rather than a species complex) and is closely related to O. hexactis (a separate species). Since their recent divergence in the mid‐Pleistocene, O. victoriae and O. hexactis likely persisted differently throughout glacial maxima, in deep‐sea and Antarctic island refugia, respectively. Genetic connectivity, within and between the Antarctic continental shelf and islands, was also observed and could be linked to the Antarctic Circumpolar Current and local oceanographic regimes. Signatures of a probable seascape corridor linking connectivity between the Scotia Sea and Prydz Bay are also highlighted. We suggest that survival in Antarctic island refugia was associated with increase in arm number and a switch from broadcast spawning to brooding in O. hexactis, and propose that it could be linked to environmental changes (such as salinity) associated with intensified interglacial‐glacial cycles. [ABSTRACT FROM AUTHOR]

Aim: Genetic connectivity is a key component of species resilience to climate change in terms of recovery capacity following disturbance and capacity to disperse to novel locations as the climate warms and isotherms shift poleward. We aimed to strengthen our understanding of resilience in this context by characterizing patterns of connectivity and genetic diversity in a broadcast spawning coral across a tropical-- temperate transition zone. We hypothesize genetic differentiation between tropical and temperate populations and decreasing genetic diversity with higher latitudes. Location: Western Australia (WA). Taxon: Turbinaria species complex. Turbinaria reniformis' Oken, 1815 (Scleractinia: Dendrophylliidae). Methods: A total of 930 target corals were sampled from 10 locations between 13 and 32° latitude spanning a 9°C mean temperature range. In situ species identification of T. reniformis is hindered by morphological plasticity and homoplasy with sister species. We combined Sanger sequencing of two mitochondrial DNA markers and high-throughput genotyping by sequencing (GBS) to isolate a single genetic Turbinaria lineage from our dataset through which patterns of genetic flow and diversity along the WA coastline could be explored using population- and individual-based clustering analyses. Results: Mitochondrial DNA sequence variation was low among Turbinaria samples and could not resolve individual species. Using GBS, we identified three genetically distinct lineages. Subsequent analyses within one of these lineages revealed strong spatial subdivision with 2-3 genetic clusters. While temperate populations were genetically diverged from more tropical sites, we did not observe declines in genetic diversity with latitude. Main conclusions: Tropical populations of T. 'reniformis' in Western Australia exhibit strong genetic connectivity, which extends to a southern limit at sub-tropical Shark Bay. Temperate populations are genetically isolated from their tropical counterparts but have relatively high genetic diversity. While the maintenance of genetic variation in temperate populations may provide some resilience to future climate scenarios, their isolation may increase their vulnerability. [ABSTRACT FROM AUTHOR]

Numerous faunistic and ecological studies have been conducted throughout the Indo-Pacific Ocean to assess its biodiversity. Despite the abundance of research, studies on the species that inhabit the Indo-Pacific are still necessary due to its extent and high species richness. The major species richness of the genus Okenia Menke, 1830 (Nudibranchia, Goniodorididae) is found in the Indo-Pacific Ocean, including 38 of 60 valid species. Nevertheless, this number does not represent the real biodiversity, since at least 20 more species are already reported in field-guides as undescribed species belonging to this genus. The systematics of the genus Okenia are still unclear since it has been the subject of only a few and incomplete studies. In the present paper, we describe five new Okenia species from the coastlines of Japan, Mozambique and Australia: Okenia aurorapapillata sp. nov., Okenia elisae sp. nov., Okenia nakanoae sp. nov., Okenia siderata sp. nov. and Okenia tenuifibrata sp. nov. Moreover, anatomical details not previously described of Okenia atkinsonorum , Okenia barnardi , Okenia cf. echinata , Okenia hallucigenia , Okenia hiroi , Okenia japonica , Okenia pellucida , Okenia pilosa and Okenia rhinorma are provided. New partial sequences of standard markers (COI , 16S rRNA and H3) were obtained and a phylogenetic analysis that included all species with available data was performed. ZOOBANK urn:lsid:zoobank.org:pub:28AE2536-A264–4194–8AE3-C430620572E7 Currently, the largest number of known Okenia species are inhabiting the Indo-Pacific. However, ~20 species are still reported as undescribed in field-guides to this genus. In the present paper, we obtain new DNA sequences for Okenia species and study their evolutionary relationships. Moreover, we describe five new Okenia species from the coastlines of Japan, Mozambique and Australia: Okenia aurorapapillata sp. nov., Okenia elisae sp. nov., Okenia nakanae sp. nov., Okenia siderata sp. nov. and Okenia tenuifibrata sp. nov. [ABSTRACT FROM AUTHOR]