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The deep-sea holothurian Chiridota heheva Pawson & Vance, 2004 was recently recognised as a cosmopolitan species which exploits the organic enrichment at three types of deep-sea reducing environments: hydrothermal vents, cold seeps, and organic falls. Here, we apply phylogenetic reconstruction and species delimitation approaches using new COI and 12S sequence data to show that C. heheva is genetically congruent with the only other hydrothermal vent holothurian, Chiridota hydrothermica Smirnov & Gebruk, 2000, with strong supporting morphological, ecological, and biogeographical parallels between the two. As such, we propose that C. heheva is a junior synonym of C. hydrothermica, and that subsequent chiridotid holothurians discovered at deep-sea reducing environments likely also belong to this single globally distributed species. As a species endemic to deep-sea reducing environments yet known at sites across the Atlantic, Indian, and Pacific Oceans, this unique holothurian provides an interesting case study for connectivity, biogeography, and speciation in the deep sea, which has important implications for deep-sea conservation planning. [ABSTRACT FROM AUTHOR]

Cold seeps support fragile deep-sea communities of high biodiversity and are often found in areas with high commercial interest. Protecting them from encroaching human impacts (bottom trawling, oil and gas exploitation, climate change) requires an advanced understanding of the drivers shaping their spatial distribution and biodiversity. Based on the analysis of 2,075 high-quality images from six remotely operated vehicle dives, we examined cold seep megabenthic community composition, richness, density, and biodiversity at a relatively shallow (∼400 m water depth) site near Baltimore Canyon (BC) and a much deeper site (∼1,500 m) near Norfolk Canyon (NC), in the northwest Atlantic. We found sharp differences in the megabenthic composition between the sites, which were driven mostly by bathymetric gradients. At both BC and NC there were significant differences in megabenthic composition across habitats. Hard habitats in and around cold seeps had significantly higher values of species richness, density, and biodiversity than soft habitats. Depth and habitat complexity were the leading environmental variables driving megabenthic variability. The presence of microbial mats and gas bubbling sites had a statistically significant contribution to explaining megabenthic variability mainly in the shallower BC and less in the deeper NC areas examined; drivers behind this discrepancy could be related to differences between BC and NC in terms of chemical compound fluxes and megafaunal life history characteristics. Our surveys revealed marine litter, primarily from commercial fisheries. This study highlights the importance of habitat complexity for the proliferation of highly diverse cold-seep ecosystems and underscores the importance of discovery science to inform spatial management of human activities in the deep and open ocean.

Chemosynthetic ecosystems have long been acknowledged as key areas of enrichment for deep-sea life, supporting hundreds of endemic species. Echinoderms are among the most common taxa inhabiting the periphery of chemosynthetic environments, and of these, chiridotid holothurians are often the most frequently observed. Yet, published records of chiridotids in these habitats are often noted only as supplemental information to larger ecological studies and several remain taxonomically unverified. This study therefore aimed to collate and review all known records attributed to Chiridota Eschscholtz, 1829, and to conduct the first phylogenetic analysis into the relationship of these chiridotid holothurians across global chemosynthetic habitats. We show that Chiridota heheva Pawson & Vance, 2004 is a globally widespread, cosmopolitan holothurian that occupies all three types of deep-sea chemosynthetic ecosystem—hydrothermal vents, cold seeps and organic falls—as an organic-enrichment opportunist. Furthermore, we hypothesise that C. heheva may be synonymous with another vent-endemic chiridotid, Chiridota hydrothermica Smirnov et al., 2000, owing to the strong morphological, ecological and biogeographical parallels between the two species, and predict that any chiridotid holothurians subsequently discovered at global reducing environments will belong to this novel species complex. This study highlights the importance of understudied, peripheral taxa, such as holothurians, to provide insights to biogeography, connectivity and speciation at insular deep-sea habitats. [ABSTRACT FROM AUTHOR]

Dorvilleidae is a diverse group of annelids found in many marine environments and also commonly associated with chemosynthetic habitats. One dorvilleid genus, Parougia , currently has 11 described species, of which two are found at vents or seeps: Parougia wolfi and Parougia oregonensis. Eight new Parougia species are recognised and described in this study from collections in the Pacific Ocean, all from whale-falls, hydrothermal vents, or methane seeps at ~600-m depth or greater. The specimens were studied using morphology and phylogenetic analyses of DNA sequences from mitochondrial (cytochrome c oxidase subunit I, 16S rRNA, and cytochrome b) and nuclear (18S rRNA and histone 3) genes. Six sympatric Parougia spp. were found at Hydrate Ridge, Oregon, while three of the Parougia species occurred at different types of chemosynthetic habitats. Two new species were found over wide geographical and bathymetric ranges. Another dorvilleid genus, Ophryotrocha , has previously been highlighted as diversifying in the deep-sea environment. Our results document the hitherto unknown diversity of another dorvilleid genus, Parougia , at various chemosynthetic environments. http://zoobank.org/urn:lsid:zoobank.org:pub:EC7EBBEA-2FB5-43D6-BE53-1A468B541A5C We present an updated phylogeny of the dorvilleid annelid genus Parougia , with the addition of new DNA sequence data from Pacific Ocean specimens from methane 'cold' seeps, hydrothermal vents and a whale-fall. Eight new species are described, and species ranges are documented across up to 6000 km along the eastern Pacific Margin. [ABSTRACT FROM AUTHOR]

Members of Calamyzinae, a clade of free-living and ectoparasitic chrysopetalids, are mainly associated with deep-sea chemosynthetic environments. The three currently known free-living calamyzin species are placed in Vigtorniella. A new free-living calamyzin species similar to these is described here. Phylogenetic analyses of Calamyzinae using mitochondrial (cytochrome c oxidase subunit I and 16S rDNA) and nuclear ( Histone H3 and 18S rDNA) loci showed that Vigtorniella and the new species form a grade with respect to an ectoparasitic clade, requiring two new genera to be erected. All free-living calamyzins show a similar anterior end and chaetal morphology. Micospina auribohnorum gen. et sp. nov. is described for the small-bodied new species from deep-sea whale falls off California and methane seeps off Costa Rica. The maximum-likelihood and Bayesian analyses show Micospina gen. nov. as sister to the ectoparasitic clade. Boudemos gen. nov. is named for the clade of two larger-bodied species: Boudemos flokati gen. et comb. nov. and Boudemos ardabilia gen. et comb. nov., which is sister group to all other Calamyzinae. Vigtorniella is retained for the type species, Vigtorniella zaikai (Kiseleva, 1992), with the adults found amongst bacterial mats at the boundary of the hydrogen sulphide zone in the Black Sea. Micospina gen. nov., Boudemos gen. nov., and Vigtorniella form a grade of free-living taxa that is associated with feeding on organic-enriched sediments, and the latter two taxa display ontogenetic jaw change. Jaws are absent in Micospina auribohnorum gen. et sp. nov. and most of the calamyzin clade of parasitic forms. [ABSTRACT FROM AUTHOR]

Abstract: Many new species of animals have been discovered during the past 40 years of deep-ocean exploration, particularly in chemosynthetic habitats such as hydrothermal vents and cold-water hydrocarbon seeps. Estimating species diversity in these environments is difficult, however, because insufficient sampling often fails to capture the range of organismic variability in time and space. Molecular systematic studies have revealed a number of taxonomic problems that derive from insufficient sampling and a shallow knowledge base regarding many deep-sea taxa. For example, numerous morphologically cryptic species exist among the vesicomyid clams and lepetodrilid limpets that dominate vents and seeps worldwide, suggesting that species richness may be significantly underestimated in these taxa. In contrast, discrete morphotypes of siboglinid tubeworms that are products of developmental plasticity were assigned synonymous species names. Also, distinct juvenile and adult forms of vent shrimp were assigned synonymous genus and species names. Though molecular studies have resolved many of these problems, they are not a panacea because they also suffer from insufficient sampling of taxa and genes, and from contamination of DNA sequences. Working carefully together, molecular and traditional systematists should eventually generate more accurate species lists that allow unbiased estimates of species richness in deep-sea environments. [Copyright &y& Elsevier]

With the discovery of Ophel, a chemosynthesis-based continental subterranean environment (Por 2007), it became evident that such environments, previously known only from the sea, are spanning the world as a parallel biosphere, the deuterobiosphere. In this preliminary contribution the different known biomes of the deuterobiosphere are reviewed and some general and comparative features are listed. [ABSTRACT FROM AUTHOR]

While the Mid-Atlantic Region is a frequented migration route for multiple cetacean species, to date no whale falls have been encountered or studied in the area. In 2015, a juvenile sperm whale was sunk south of Faial (Azores, Portugal), implanted at 760m depth and its decomposition was monitored for one year with seven submersible dives. Based on imagery, two different successional stages were observed: the mobile/scavenging stage characterised by sharks and 3 different species of decapods and the enrichment/opportunistic stage, dominated by polychaetes. While all scavengers were known background fauna for the region, whale fall specialist fauna was observed during the enrichment-opportunistic stage, including bone-eating worms (Osedax spp.). After one year at the bottom, a vertebra and a rib were sampled to assess the species composition. While all Polychaeta, Arthropoda and Mollusca families were known from whale falls, few could be identified to species level, indicating species new to science. Based on the presence of sulphide tolerant organisms (Mytilidae aff. Bathymodiolinae and Polycladida, Platyhelminthes) in the samples, a transition to the chemosynthetic-based stage appeared to have been initiated. Taxon overlap at genus and possible species level of some Polychaeta was observed with the cow fall off the coast of Portugal (Ophryotrocha cf. lusa and O. cf. sadina) and with the whale fall off the coast of Brazil (Pleijelius , Sirsoe syn. Vrijenhoekia), thus connecting both sides of the Atlantic Ocean. • First whale fall on the Mid-Atlantic Ridge. • Two successional stages were visually observed over the course of 1 year. • Transition to the third sulphophilic stage was initiated. • Whale fall specialist fauna connects with other organic falls across the Atlantic. [ABSTRACT FROM AUTHOR]