BackgroundSclerolinum (Annelida: Siboglinidae) is a genus of small, wiry deep-sea tubeworms that depend on an endosymbiosis with chemosynthetic bacteria for their nutrition, notable for their ability to colonise a multitude of reducing environments. Since the early 2000s, a Sclerolinum population has been known to inhabit sediment-hosted hydrothermal vents within the Bransfield Strait, Southern Ocean, and whilst remaining undescribed, it has been suggested to play an important ecological role in this ecosystem. Here, we show that the Southern Ocean Sclerolinum population is not a new species, but more remarkably in fact belongs to the species S. contortum, first described from an Arctic mud volcano located nearly 16,000 km away.ResultsOur new data coupled with existing genetic studies extend the range of this species across both polar oceans and the Gulf of Mexico. Our analyses show that the populations of this species are structured on a regional scale, with greater genetic differentiation occurring between rather than within populations. Further details of the external morphology and tube structure of S. contortum are revealed through confocal and SEM imaging, and the ecology of this worm is discussed.ConclusionsThese results shed further insight into the plasticity and adaptability of this siboglinid group to a range of reducing conditions, and into the levels of gene flow that occur between populations of the same species over a global extent.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0559-y) contains supplementary material, which is available to authorized users.

The genus Scaphander (Gastropoda, Cephalaspidea) is a group of predominantly deep‐sea, soft‐bottom snails with extant species distributed worldwide from the Arctic to the Antarctic. There are approximately 45 species described worldwide, of which about 18 are considered to be valid. The systematics of Scaphander has traditionally been shell‐based, but shell characters often show high intraspecific variability, and this led to a high number of nominal names available of unclear taxonomic status. The main objectives of this article are to revise the systematics of the Atlantic species of Scaphander, and to produce an identification key and a molecular phylogeny to aid with species delimitation. The validity of species was assessed following an integrative approach combining the study of type material and original descriptions, shells, morpho‐anatomical characters, and molecular phylogenetics. Anatomical structures were documented by drawings, macro‐photography, and scanning electron microscopy (SEM). Two mitochondrial (COI and 16S rRNA) and one nuclear (28S rRNA) genes were sequenced, and Bayesian molecular phylogenetic hypotheses were produced. Representatives of the Cephalaspidean genera Bulla and Haminoea were included to test the monophyly of Scaphander. Eight species of Scaphander were recognized in the Atlantic Ocean. Three species are restricted to the western Atlantic (Scaphander clavus, Scaphander darius, and Scaphander watsoni), one is distributed only in the eastern Atlantic (Scaphander lignarius), one is endemic to the Azores (Scaphander gracilis; this species is only known from shells), and three have amphi‐Atlantic distributions (Scaphander bathymophilus, Scaphander nobilis, and Scaphander punctostriatus). Shell characters and the morphology of the male reproductive system were found to be the best diagnostic characters for species recognition. The molecular phylogeny confirms the monophyly of Scaphander, and is largely congruent with species delimitation based on morpho‐anatomical characters. © 2013 The Linnean Society of London

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The paradigm of large geographic ranges in the deep sea has been challenged by genetic studies, which often reveal putatively widespread species to be several taxa with more restricted ranges. Recently, a phylogeographic study revealed that the tubeworm Sclerolinum contortum (Siboglinidae) inhabits vents and seeps from the Arctic to the Antarctic. Here, we further test the conspecificity of the same populations of S. contortum with additional mitochondrial and nuclear markers. We also investigate the genetic connectivity of another species with putatively the same wide geographic range - Nicomache lokii (Maldanidae). Our results support the present range of S. contortum, and the range of N. lokii is extended from vents and seeps in the Nordic Seas to mud volcanoes in the Barbados Trench and Antarctic vents. Sclerolinum contortum shows more pronounced geographic structure than N. lokii, but whether this is due to different dispersal capacities or reflects the geographic isolation of the sampled localities is unclear. Two distinct mitochondrial lineages of N. lokii are present in the Antarctic, which may result from two independent colonization events. The environmental conditions inhabited by the two species and implications for their distinct habitat preference is discussed.

BackgroundA range of higher animal taxa are shared across various chemosynthesis-based ecosystems (CBEs), which demonstrates the evolutionary link between these habitats, but on a global scale the number of species inhabiting multiple CBEs is low. The factors shaping the distributions and habitat specificity of animals within CBEs are poorly understood, but geographic proximity of habitats, depth and substratum have been suggested as important. Biogeographic studies have indicated that intermediate habitats such as sedimented vents play an important part in the diversification of taxa within CBEs, but this has not been assessed in a phylogenetic framework. Ampharetid annelids are one of the most commonly encountered animal groups in CBEs, making them a good model taxon to study the evolution of habitat use in heterotrophic animals. Here we present a review of the habitat use of ampharetid species in CBEs, and a multi-gene phylogeny of Ampharetidae, with increased taxon sampling compared to previous studies.ResultsThe review of microhabitats showed that many ampharetid species have a wide niche in terms of temperature and substratum. Depth may be limiting some species to a certain habitat, and trophic ecology and/or competition are identified as other potentially relevant factors. The phylogeny revealed that ampharetids have adapted into CBEs at least four times independently, with subsequent diversification, and shifts between ecosystems have happened in each of these clades. Evolutionary transitions are found to occur both from seep to vent and vent to seep, and the results indicate a role of sedimented vents in the transition between bare-rock vents and seeps.ConclusionThe high number of ampharetid species recently described from CBEs, and the putative new species included in the present phylogeny, indicates that there is considerable diversity still to be discovered. This study provides a molecular framework for future studies to build upon and identifies some ecological and evolutionary hypotheses to be tested as new data is produced.Electronic supplementary materialThe online version of this article (10.1186/s12862-017-1065-1) contains supplementary material, which is available to authorized users.