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The general morphology of the body, including the distribution of putative sensory ciliary cells, was studied using scanning electron microscopy (SEM) in the siboglinid Nereilinum murmanicum Ivanov, 1961 collected from the Barents Sea and at a new, deeper locality in the Greenland Sea outside the known range of this species. The fine features of cuticular structures in N. murmanicum, including the bridle and cuticular plaques from different parts of the body, were described for the first time. Since we have previously shown in the closely related siboglinid Oligobrachia haakonmosbiensis Smirnov, 2000 using SEM and confocal laser scanning microscopy (CLSM) that all epidermal cilia except for the ventral ciliary band belong to sensory cells, we consider all ciliary structures detected in N. murmanicum as sensory. The tentacles, clusters of ciliary cells along the dorsal furrow, areas around the openings of the multicellular glands, papillae, and the ciliary patch located on the cephalic lobe at the base of the tentacles can be regarded as specialized sensory areas. Based on our current knowledge of sensory structures in annelids, a number of assumptions were made about possible functional characteristics of putative sensory structures in siboglinids. [ABSTRACT FROM AUTHOR]

Frenulates are a group of sedentary Annelida within the family Siboglinidae that inhabit the ocean floor and present a unique challenge for comprehensive molecular and phylogenetic investigations. In this study, we focused on the frenulates, specifically assembling the mitochondrial genomes of Siboglinum plumosum and Oligobrachia dogieli. The phylogenetic reconstruction placed S. plumosum as a sister taxon to S. ekmani, and O. dogieli as a sister taxon to S. fiordicum, supporting the non-monophyletic nature of the genus Siboglinum. Overall, this study supports the phylogeny of the family Siboglinidae while highlighting the need for additional molecular data within frenulates. [ABSTRACT FROM AUTHOR]

First described in 2004 off California, Osedax worms are now known from many of the world's oceans, ranging from 10 to over 4000 m in depth. Currently, little is known about species ranges, since most descriptions are from single localities. In this study, we used new sampling in the north-eastern Pacific and available GenBank data from off Japan and Brazil to report expanded ranges for five species: Osedax frankpressi, O. knutei, O. packardorum, O. roseus and O. talkovici. We also provided additional DNA sequences from previously reported localities for two species: Osedax priapus and O. randyi. To assess the distribution of each species, we used cytochrome c oxidase subunit I (COI) sequences to generate haplotype networks and assess connectivity amongst localities where sampling permitted. Osedax frankpressi, O. packardorum, O. priapus, O. roseus and O. talkovici all had one or more dominant COI haplotypes shared by individuals at multiple localities, suggesting high connectivity throughout some or all of their ranges. Low F values amongst populations for O. packardorum, O. roseus and O. talkovici confirmed high levels of gene flow throughout their known ranges. High F values for O. frankpressi between the eastern Pacific and the Brazilian Atlantic showed little gene flow, reflected by the haplotype network, which had distinct Pacific and Atlantic haplotype clusters. This study greatly expands the ranges and provides insights into the phylogeography for these nine species. [ABSTRACT FROM AUTHOR]

Macrofauna can contribute substantially to the organic matter cycling on the seafloor, yet the role of terrestrial and chemosynthetic organic matter in the diets of microphagous (deposit and suspension) feeders is poorly understood. In the present study, we used stable isotopes of carbon and nitrogen to test the hypothesis that the terrestrial organic matter supplied with river runoff and local chemosynthetic production at methane seeps might be important organic matter sources for macrofaunal consumers on the Laptev Sea shelf. We sampled locations from three habitats with the presumed differences in organic matter supply: "Delta" with terrestrial inputs from the Lena River, "Background" on the northern part of the shelf with pelagic production as the main organic matter source, and "Seep" in the areas with detected methane seepage, where chemosynthetic production might be available. Macrobenthic communities inhabiting each of the habitats were characterized by a distinct isotopic niche, mostly in terms of δ13C values, directly reflecting differences in the origin of organic matter supply, while δ15N values mostly reflected the feeding group (surface deposit/suspension feeders, subsurface deposit feeders, and carnivores). We conclude that both terrestrial and chemosynthetic organic matter sources might be substitutes for pelagic primary production in the benthic food webs on the largely oligotrophic Laptev Sea shelf. Furthermore, species-specific differences in the isotopic niches of species belonging to the same feeding group are discussed, as well as the isotopic niches of the symbiotrophic tubeworm Oligobrachia sp. and the rissoid gastropod Frigidoalvania sp., which are exclusively associated with methane seeps. [ABSTRACT FROM AUTHOR]

Biodiversity in the Laptev Sea was assessed for gutless marine worms of the family Siboglinidae (Annelida), whose metabolism is provided by symbiotic bacteria that oxidize hydrogen sulfide and methane. Seven siboglinid species were found within the geographical boundaries of the Laptev Sea, and another species was found in an adjacent sector of the Arctic Basin. The largest number of finds and the greatest biological diversity of siboglinids were observed in the eastern part of the Laptev Sea in a field of numerous methane flares. One find was made in the estuary area of the Lena River at a depth of 25 m. A possible association of siboglinids with methane seepage areas is discussed. [ABSTRACT FROM AUTHOR]

The discovery of new occurrences of pogonophores Siboglinum sp. and Nereilinum sp. from the St. Anna Trough (northwestern portion of the Kara Sea) is described in this paper. Previously, occurrences of pogonophores (Crispabrachia yenisey and Galathealinum karaense) were reported in the southern part of the Kara Sea, in the estuary of the Yenisei River. Two areas in the Kara Sea where pogonophores were found coincide with the regions of distribution of two types of gas hydrates: oceanic seafloor gas hydrates, and gas hydrates associated with permafrost. Gas hydrate deposits in the permafrost are confined to the coastal regions of the Kara Sea. A methane flux forms in areas of dissociation of gas hydrates under the influence of river runoff. This methane source is vital for the survival of pogonophores. The existence of pogonophores in the St. Anna Trough indicates the presence of a methane flux associated with the inflow of Atlantic water, which causes dissociation of seafloor gas hydrates. The possible role of Arctic warming is apparent in both processes. [ABSTRACT FROM AUTHOR]

Representatives of pogonophorans (Annelida, Siboglinidae), whose vital activity is provided by symbiotic chemoautotrophic bacteria that oxidize methane and hydrogen sulfide, were found in the St. Anna Trough at depths of 539 and 437 m. The finding of pogonophorans suggests high concentrations of methane, which might result from dissociation of bottom gas hydrates under the influence of the influx of warm Atlantic water into the Kara Sea along the St. Anna Trough. [ABSTRACT FROM AUTHOR]

Abstract Background The nervous system of siboglinids has been studied mainly in Osedax and some Vestimentifera, while data in Frenulata – one of the four pogonophoran main branches – is still fragmentary. In most of the studies, the focus is almost always on the central nervous system, while the peripheral nervous system has traditionally received little attention. In contrast to other annelids, the structure and diversity of sensory structures in siboglinids are still quite undescribed. Meanwhile, the peripheral nervous system, as well as sensory elements, are extremely evolutionarily labile, and information about their organization is of high importance to understand lifestyles and behavior as well as main trends that lead siboglinids to their peculiar organization. Results The structure of the peripheric nervous system, sensory elements, and neuromuscular relationships of Oligobrachia haakonmosbiensis were studied using both scanning electron and confocal laser microscopy. A significant number of monociliary sensory cells, as well as sensory complexes located diffusely in the epithelium of the whole body were revealed. The latter include the cephalic tentacles, sensory cells accumulations along the dorsal furrow and ciliary band, areas of the openings of the tubiparous glands, and papillae. The oval ciliary spot located on the cephalic lobe at the base of the tentacles can also be regarded as a sensory organ. Most of the detected sensory cells show immunoreactivity to substance P and/or acetylated α-tubulin. FMRFamide- and serotonin-like immunoreactivity are manifested by neurons that mainly innervate tentacles, muscles, body wall epithelium, skin glands, tubiparous glands, and papillae. In the larva of O. haakonmosbiensis, monociliary sensory elements were revealed in the region of the apical organ, along the body, and on the pygidium. Conclusions The diversity of sensory structures in O. haakonmosbiensis comprises epidermal solitary sensory cells, sensory spots around tubiparous glands openings, and putative sensory organs such as cephalic tentacles, an oval ciliary spot on the cephalic lobe, the dorsal furrow, and papillae. Sensory structures associated with papillae and tubiparous glands play presumable mechanosensory functions and are associated with regulation of tube building as well as anchorage of the worm inside the tube. Sensory structures of the dorsal furrow are presumably engaged in the regulation of reproductive behavior. An overall low level of morphological differentiation of O. haakonmosbiensis peripheral nervous system is not typical even for annelids with the intraepithelial nervous system. This can be considered as a plesiomorphic feature of its peripheral plexus’s organization, or as evidence for the neotenic origin of Siboglinidae.

This article deals with the external and internal morphology in the adult stages of Nereilinum murmanicum Ivanov, 1961, a widespread species of Siboglinidae in the Barents Sea. Since Siboglinidae is currently a taxon within the phylum Annelida, we revised the commonly held view of the body segmentation pattern typical of the species and provided the first des­cription of its opisthosoma. Furthermore, the postannular region and trophosome were structurally analyzed using histology and electron microscopy. The endodermal origin of the trophosome was suggested from its structure and position. The juvenile and larval stages of the species were described. The early larvae were found to resemble the trochophores in Annelida. The late larvae look like the late metatrochophora in Annelida and lack parapodia. The juvenile specimens retain no larval traits and are morphologically comparable to the adult stages. New data on the ecology of the species were obtained: it appears to also inhabit deeper water layers. The boundaries of its range in the Barents Sea were expanded and specified. The abundance distribution of the species in the Barents Sea (30–40 ind/m2 for the major part of the sea, up to 72–113 ind/ m2 for certain areas of the sea in particular years) was considered.

The article describes the parameters of maintaining the gutless symbiotrophic annelid Siboglinum fiordicum in laboratory conditions outside the marine environment for 64 days. [ABSTRACT FROM AUTHOR]

The fine structure of the body wall and gut was for the first time studied in the competent larvae of the frenulate pogonophoran Siboglinum fiordicum. Mass apoptosis of cell nuclei was observed in the dermo-muscular body wall and coelomic epithelium. Apoptotic nuclei were found in both cell cytoplasm and outside of the larval body. In the latter case, each nucleus was surrounded by the plasmalemma, and the entire cluster was covered with the cuticle. Cells of the larval gut retained the usual structure with the cytoplasm filled with numerous yolky granules and the nucleus displaying usual morphology. Similar apoptotic processes have been described in vestimentiferans and found to be initiated by penetration of symbiotic bacteria through the integument into the dorsal mesentery. The process of apoptotic rearrangement of body wall cells and the formation of unique symbiosis with bacteria were assumed to be time-spaced in S. fiordicum, occurring sequentially rather than simultaneously, unlike in vestimentiferans. [ABSTRACT FROM AUTHOR]

Gutless marine worms of the family Siboglinidae have been found in the estuaries of the largest Arctic rivers Yenisei, Lena, and Mackenzie. Siboglinid metabolism is provided by symbiotic chemoautotrophic bacteria. Strong salinity stratification is characteristic of the estuaries of the largest Arctic rivers and ensures a high salinity at depths of 25–36 m, where siboglinids were found. High methane concentrations, which are necessary for siboglinid metabolism, result from dissociation of permafrost gas hydrates under the influence of river runoff in the conditions of Arctic warming. [ABSTRACT FROM AUTHOR]

The genetic structure of the vestimentiferan Lamellibrachia satsuma (Annelida: Siboglinidae) distributed in Kagoshima Bay, southwestern Japan, and the Nikko and Daikoku seamounts on the northern Mariana Arc, was analyzed using 14 newly developed microsatellite markers. We detected large genetic differences between the L. satsuma distributed in Japanese and Mariana waters, whereas no significant divergence was detected between local populations inhabiting the calderas of the two Mariana seamounts, which are separated by a distance of approximately 270 km. STRUCTURE analysis revealed that two genetically distinct clusters are dominant and no genetic differentiation was detected between sampling years or sites in Kagoshima Bay. We speculated that the Kagoshima Bay population is derived from individuals that have immigrated relatively recently from two undiscovered habitats in waters outside of the bay. [ABSTRACT FROM AUTHOR]

Background: The nervous system of siboglinids has been studied mainly in Osedax and some Vestimentifera, while data in Frenulata – one of the four pogonophoran main branches – is still fragmentary. In most of the studies, the focus is almost always on the central nervous system, while the peripheral nervous system has traditionally received little attention. In contrast to other annelids, the structure and diversity of sensory structures in siboglinids are still quite undescribed. Meanwhile, the peripheral nervous system, as well as sensory elements, are extremely evolutionarily labile, and information about their organization is of high importance to understand lifestyles and behavior as well as main trends that lead siboglinids to their peculiar organization. Results: The structure of the peripheric nervous system, sensory elements, and neuromuscular relationships of Oligobrachia haakonmosbiensis were studied using both scanning electron and confocal laser microscopy. A significant number of monociliary sensory cells, as well as sensory complexes located diffusely in the epithelium of the whole body were revealed. The latter include the cephalic tentacles, sensory cells accumulations along the dorsal furrow and ciliary band, areas of the openings of the tubiparous glands, and papillae. The oval ciliary spot located on the cephalic lobe at the base of the tentacles can also be regarded as a sensory organ. Most of the detected sensory cells show immunoreactivity to substance P and/or acetylated α-tubulin. FMRFamide- and serotonin-like immunoreactivity are manifested by neurons that mainly innervate tentacles, muscles, body wall epithelium, skin glands, tubiparous glands, and papillae. In the larva of O. haakonmosbiensis, monociliary sensory elements were revealed in the region of the apical organ, along the body, and on the pygidium. Conclusions: The diversity of sensory structures in O. haakonmosbiensis comprises epidermal solitary sensory cells, sensory spots around tubiparous glands openings, and putative sensory organs such as cephalic tentacles, an oval ciliary spot on the cephalic lobe, the dorsal furrow, and papillae. Sensory structures associated with papillae and tubiparous glands play presumable mechanosensory functions and are associated with regulation of tube building as well as anchorage of the worm inside the tube. Sensory structures of the dorsal furrow are presumably engaged in the regulation of reproductive behavior. An overall low level of morphological differentiation of O. haakonmosbiensis peripheral nervous system is not typical even for annelids with the intraepithelial nervous system. This can be considered as a plesiomorphic feature of its peripheral plexus's organization, or as evidence for the neotenic origin of Siboglinidae. [ABSTRACT FROM AUTHOR]

The anatomical and histological structure of the trophosome of the giant vestimentiferan Riftiapachyptila has been studied. The trophosome consists of longitudinally oriented cords. The cords of the trophosome intertwine, form diverticula and anastomose with each other. Each cord has an axial blood vessel inside, which is connected to afferent vessels on the surface of the cord by radial capillaries. Based on the data on the structure and development of the trophosome, it is suggested that the evolutionary precursor of the trophosome was a blood network connecting the ventral and dorsal vessels. The cells of the coelomic lining on the surface of the vessels grew and gave rise to the parenchymal tissue of the trophosome. At the same time, the trophosome developed from two sources, namely: due to the coelomic lining on the surface of the vessels of the intestinal plexus and due to the coelomic lining on the surface of the vessels of the circulatory plexus of the body wall. [ABSTRACT FROM AUTHOR]

The article presents a report on the findings of representatives of frenulate pogonophorans Nereilinum murmanicum in the northern and central parts of the Barents Sea, which significantly expands the range of this species and provides guidance on its distribution in this basin. Here we present the coordinates of new finds with an indication of the depth. Find points were associated with data on known and potential hydrocarbon deposits. [ABSTRACT FROM AUTHOR]

Only seven frenulate species are currently known along the Eurasian coast of the Arctic Ocean. We describe a new genus and a new species of frenulates Crispabrachia yenisey , gen. nov. et sp. nov. The morphological analysis involved standard anatomical techniques, semithin sections and scanning electron microscopy (SEM). The molecular study included four markers (partial COI , 16S , 18S and 28S) and implemented Bayesian and Maximum likelihood phylogenetic approaches. The description of Crispabrachia gen. nov. is the first documented finding of frenulates in the Kara Sea at the estuary of the Yenisey River in rather shallow water (28 m). The establishment of a new genus is warranted based on the composition of morphological characters and several specific features including free, comparatively short curly tentacles, a triangular cephalic lobe with amplate base, the valvate extension of the posterior part of the forepart and prominent papillae on the nonmetameric region. The tube structure with prominent frills and the worm's numerous tentacles, metameric papillae with cuticular plaques and segmental furrow on the forepart indicate that the new genus belongs to the polybrachiid group. Although the type locality in the Yenisey River estuary is unusual for siboglinids in general, the physical conditions here are common for other frenulates habitats, i.e. salinity ~30–33, bottom water temperature –1.5°C. This finding was made in the Yenisey Gulf in the region with the highest methane concentrations in the southern part of the Kara Sea that reflects permafrost degradation under the influence of river flow. Further study of the region would help to understand the factors influencing frenulate distributions and improve our knowledge of their biodiversity. Only seven frenulate species are currently known along the Eurasian coast of the Arctic Ocean. In this paper, we describe a new genus and a new species of frenulates – Crispabrachia yenisey , gen. nov. et sp. nov. Here we present the morphological analysis of new genus. The molecular study included four markers (partial COI , 16S , 18S and 28S) and implemented Bayesian and Maximum likelihood phylogenetic approaches. The description of Crispabrachia gen. nov. is the first documented finding of frenulates in the Kara Sea at the estuary of the Yenisey River in rather shallow water (28 m). [ABSTRACT FROM AUTHOR]

Pogonophora or siboglinid tubeworms (Annelida, Siboglinidae) have been found in the East Siberian Sea for the first time. On the basis of the results of molecular phylogenetic analysis, the found specimens are presumably assigned to the genus Oligobrachia. The stations where the siboglinid tubeworms have been found are located in the area of methane seeps. This confirms the previously stated hypothesis about relationship of siboglinid tubeworm distribution with the areas of underwater methane seeps. [ABSTRACT FROM AUTHOR]

Large parcels of organic matter in the deep sea, such as whale carcasses, harbor a very specialized fauna, most famously the bone-eating worms in the genus Osedax (Annelida, Siboglinidae). Although Osedax was first described only 15 years ago, there are already 26 described species from the Pacific, Atlantic, and Southern Oceans. The high discovery rate of new Osedax species indicates that there is still a lot of undescribed diversity. In this study we describe the most northerly species of Osedax to date, Osedax fenrisi sp. nov. from 73°N on the Arctic Mid-Ocean Ridge. We also present an updated molecular phylogeny of Osedax based on cytochrome oxidase subunit I and 18S rRNA, including all described species in the genus. The molecular results support that O. fenrisi sp. nov. is distinct from the previously known species of Osedax. Both morphological characters and the molecular phylogeny support the placement of O. fenrisi sp. nov. in clade V. The most striking morphological character shared with other described species in this clade (Osedax rubiplumus, Osedax roseus, and Osedax bryani) is the presence of long pinnules inserted on the outside of the palps. Nomenclatural act recorded in Zoobank. LSID: E55A5C87-0CB6-4146-B3D9-7E3B19B68628.

Bone-eating worms of the genus Osedax (Annelida, Siboglinidae) form unique holobionts (functional entity comprising host and associated microbiota), highly adapted to inhabit bone tissue of marine vertebrates. These gutless worms have developed nutritional symbioses housing intracellular, horizontally acquired, heterotrophic bacteria hypothesised to harness nutrients from organic compounds, sequestered within the bone. Despite previous efforts, critical mechanisms mediating activity and acquisition of diverse bacterial assemblages remain unclear. Using 16S rRNA amplicon sequencing, we performed detailed taxonomic and predicted functional analyses shedding light on the microbial communities of two shallow-water Osedax species (Osedax deceptionensis and Osedax 'mediterranea') from contrasting habitats (Antarctic and Mediterranean Sea), in two tissue types (roots and palps). Comparative assessments between host species revealed distinct microbial assemblages whilst, within host species and body tissue, relative symbiont frequencies retained high variability. We reported relatively high abundances of microbes previously classified as primary endosymbionts, Ribotype 1 (order Oceanospirillales), and diverse likely secondary epibionts warranting further exploration as recurrent Osedax associates. Surprisingly, O. 'mediterranea' exhibited relatively low abundance of Oceanospirillales, but increased abundance of other potentially hydrocarbon degrading bacteria from the family Alteromonadaceae. We hypothesise the presence of functionally similar, non-Oceanospirillales primary endosymbionts within O. 'mediterranea'. Functional metagenomic profiling (using 16S rRNA sequences) predicted broad metabolic capabilities, encompassing relatively large abundances of genes associated with amino acid metabolism. Comparative analyses between host body tissue communities highlighted several genes potentially providing critical functions to the Osedax host or that confer adaptations for intracellular life, housed within bone embedded host root tissues. [ABSTRACT FROM AUTHOR]

Frenulate siboglinids are a characteristic component of communities living in various reducing environments, including sites with hydrocarbon seeps. High concentrations of hydrocarbons in the sediments of the Arctic basin seas, including the Barents Sea, suggest the presence of a rich siboglinid fauna there. This reflects the fact that microbiological oxidation of methane occurs under reducing conditions, generating high concentrations of hydrogen sulfide in the sediment. This hydrogen sulfide acts as an energy source for the sulfide-oxidizing symbionts of siboglinids. Here we report on the findings of the frenulate siboglinid species Nereilinum murmanicum made between 1993 and 2020 in the Barents Sea. These data significantly expand the range of this species and yield new information on its habitat distribution. The depth range of N. murmanicum was 75–375 m. The species was most abundant from 200 to 350 m and was associated with temperatures below 3 °C and salinities from 34.42 to 35.07. Most of the findings (43 locations or 74%) fall on areas highly promising for oil and gas production. Twenty-eight locations (48%) are associated with areas of known oil deposits, 22 locations (37%) with explored areas of gas hydrate deposits. N. murmanicum was also found near the largest gas fields in the Barents Sea, namely Shtokman, Ludlovskoye and Ledovoye.

Allometric growth in post-embryonic development was studied in the hydrothermal vestimentiferan Oasisia alvinae Jones, 1985. In the process of growth, the length of the trunk region increases relative to the total body length from 51 to 83.4%, whereas the relative sizes of the obturacular region, vestimental region, and the opisthosoma decrease. This is connected with a strong development of the trophosome and gonads in the trunk region. It is suggested that the predominant growth of the trunk region during ontogeny is a common pattern for all vestimentiferans. We discuss the differences in body proportions of vestimentiferans that live in hydrothermal vents and vestimentiferans of cold hydrocarbon seeps. [ABSTRACT FROM AUTHOR]

[Display omitted] • Siboglinid tubeworms are found at chemosynthetic environments worldwide. • The Vestimentifera clade is well known within Siboglinidae for their reliance on bacterial symbionts. • This study provides new complete mitochondrial genomes for ten Vestimentifera. • This study provides phylogenetic analyses combining fifteen mitochondrial genes and nuclear 18S rRNA. • A new species of Alaysia is described from the Manus Basin. Siboglinid tubeworms are found at chemosynthetic environments worldwide and the Vestimentifera clade is particularly well known for their reliance on chemoautotrophic bacterial symbionts for nutrition. The mitochondrial genomes have been published for nine vestimentiferan species to date. This study provides new complete mitochondrial genomes for ten further Vestimentifera, including the first mitochondrial genomes sequenced for Alaysia spiralis , Arcovestia ivanovi , Lamellibrachia barhami , Lamellibrachia columna , Lamellibrachia donwalshi , and unnamed species of Alaysia and Oasisia. Phylogenetic analyses combining fifteen mitochondrial genes and the nuclear 18S rRNA gene recovered Lamellibrachia as sister to the remaining Vestimentifera and Riftia pachyptila as separate from the other vent-endemic taxa. Implications and auxiliary analyses regarding differing phylogenetic tree topologies, substitution saturation, ancestral state reconstruction, and divergence estimates are also discussed. Additionally, a new species of Alaysia is described from the Manus Basin. [ABSTRACT FROM AUTHOR]

Siboglinids were sampled from four mud volcanoes in the Gulf of Cádiz (El Cid MV, Bonjardim MV, Al Gacel MV, and Anastasya MV). These invertebrates are characteristic to cold seeps and are known to host chemosynthetic endosymbionts in a dedicated trophosome organ. However, little is known about their tube as a potential niche for other microorganisms. Analyses by scanning and transmission electron microscopy showed dense biofilms on the tube in Al Gacel MV and Anastasya MV specimens by prokaryotic cells. Methanotrophic bacteria were the most abundant forming these biofilms as further supported by 16S rRNA sequence analysis. Furthermore, elemental analyses with electron microscopy and energy-dispersive X-ray spectroscopy point to the mineralization and silicification of the tube, most likely induced by the microbial metabolisms. Bacterial and archaeal 16S rRNA sequence libraries revealed abundant microorganisms related to these siboglinid specimens and certain variations in microbial communities among samples. Thus, the tube remarkably increases the microbial biomass related to the worms and provides an additional microbial niche in deep-sea ecosystems.

Here we report the first finding of a frenulate pogonophoran (Annelida, Siboglinidae) in the southern part of the Kara Sea. This finding was made in the Yenisei Gulf in the region of the highest methane concentrations, resulting from the degradation of permafrost under the influence of river flow. It has been suggested that pogonophorans are indicators of hydrocarbon manifestations of various genesis. [ABSTRACT FROM AUTHOR]

We have conducted comparative analysis of the structure of the dorsal lips of the polychaete Eudistylia polymorpha from the family Sabellidae and the obturacula of Oasisia alvinae (Vestimentifera). It has been concluded that the obturacula of Vestimentifera are homologs of the dorsal lips of Polychaete from the family Sabellidae. It has been suggested that the head lobe of siboglinids of the subfamily Frenulata is homologous to the fused obturacula of Vestimentifera. [ABSTRACT FROM AUTHOR]

Methane seeps provide biogeochemical and microbial heterogeneity in deep-sea habitats. In the Northeast (NE) Pacific Ocean recent studies have found an abundance of seeps at varying spatial separations and within distinct biogeochemical environments ranging in oxygen, depth, and temperature. Here, we examine eight newly discovered seeps and two known seeps covering 800 km and varying across 2000 m water depth to identify: (1) novel megafaunal communities in this geographical region; (2) variations in the microbiome of seep habitats across the margin; (3) spatial and biogeochemical drivers of microbial diversity at seeps. In addition to authigenic carbonates, clam beds, microbial mats, and exposed hydrates - we also observed Siboglinidae tube worm bushes and an anomalous deep-sea barnacle adding to the overall habitats known from the NE Pacific. The microbial communities showed high variability in their spatial distribution and community structure. The seep communities formed distinct groups that included multiple groups of anaerobic methane oxidizing Archaea (ANME; 1, 2ab, 2c, and 3), often co-occurring within one site – however, there were also other sites with clearly dominant members (e.g. ANME-1s at Nehalem Bank). Sulfide oxidizers were dominated by the non-mat forming Campylobacterales and even though vertical gradients in redox potential typify seep sediments, in two cases there was not a significant change in community structure across the top five cm of sediment. We posit that these patterns were driven by ‘bubble-turbation,’ and bioirrigation by megafauna. A surprising latitudinal trend was observed in species diversity and richness with increasing richness significantly correlated to increasing latitude. Overall, our results demonstrate that heterogeneity is ubiquitous in the seep biome, spanning all faunal classes, and that the understanding of seeps and the drivers of the community structure can be improved by studying seeps at a range of spatial scales. [ABSTRACT FROM AUTHOR]

Background: Vestimentiferan tubeworms (Annelida: Siboglinidae) often play an important role as a foundation species in chemosynthetic ecosystems by providing microhabitats for other organisms. In the present study, we detected a new relationship between phyllodocid worms and tubes of a vestimentiferan Alaysia sp. Methods: Tubes of Alaysia sp. were collected from a hydrothermal vent field at a depth of 1052 m on the North Iheya Knoll in the Okinawa Trough on January 17, 2000. The Alaysia tubes were fixed with 4.7% neutralized formaldehyde solution and preserved in 70% ethyl alcohol. Phyllodocid worms were later obtained from empty tubes of Alaysia sp. Results: We classified the collected phyllodocid worms as Protomystides hatsushimaensis based on the morphology of specialized chaetae. They were observed in thin brownish tubes of mucous, probably secreted by P. hatsushimaensis, at approximately 30 and 50 mm from the upper openings of the tubes of Alaysia sp. Conclusions: The phyllodocid worm P. hatsushimaensis was found inside the tubes of Alaysia sp., a vestimentiferan tubeworm, collected in a hydrothermal vent field on the North Iheya Knoll in the Okinawa Trough of the western Pacific. The present study provides a new record of P. hatsushimaensis using empty vestimentiferan tubes as a microhabitat. [ABSTRACT FROM AUTHOR]

The deep sea is home to many species that have longer life spans than their shallow-water counterparts. This trend is primarily related to the decline in metabolic rates with temperature as depth increases. However, at bathyal depths, the cold-seep vestimentiferan tubeworm species Lamellibrachia luymesi and Seepiophila jonesi reach extremely old ages beyond what is predicted by the simple scaling of life span with body size and temperature. Here, we use individual-based models based on in situ growth rates to show that another species of cold-seep tubeworm found in the Gulf of Mexico, Escarpia laminata, also has an extraordinarily long life span, regularly achieving ages of 100-200 years with some individuals older than 300 years. The distribution of results from individual simulations as well as whole population simulations involving mortality and recruitment rates support these age estimates. The low 0.67% mortality rate measurements from collected populations of E. laminata are similar to mortality rates in L. luymesi and S. jonesi and play a role in evolution of the long life span of cold-seep tubeworms. These results support longevity theory, which states that in the absence of extrinsic mortality threats, natural selection will select for individuals that senesce slower and reproduce continually into their old age. [ABSTRACT FROM AUTHOR]

Deep-sea tubeworms (Annelida, Siboglinidae) represent dominant species in deep-sea chemosynthetic communities (e.g. hydrothermal vents and cold methane seeps) and occur in muddy sediments and organic falls. Siboglinids lack a functional digestive tract as adults, and they rely on endosymbiotic bacteria for energy, making them of evolutionary and physiological interest. Despite their importance, inferred evolutionary history of this group has been inconsistent among studies based on different molecular markers. In particular, placement of bone-eating Osedax worms has been unclear in part because of their distinctive biology, including harbouring heterotrophic bacteria as endosymbionts, displaying extreme sexual dimorphism and exhibiting a distinct body plan. Here, we reconstructed siboglinid evolutionary history using 12 newly sequenced transcriptomes. We parsed data into three data sets that accommodated varying levels of missing data, and we evaluate effects of missing data on phylogenomic inference. Additionally, several multispecies-coalescent approaches and Bayesian concordance analysis ( BCA) were employed to allow for a comparison of results to a supermatrix approach. Every analysis conducted herein strongly supported Osedax being most closely related to the Vestimentifera and Sclerolinum clade, rather than Frenulata, as previously reported. Importantly, unlike previous studies, the alternative hypothesis that frenulates and Osedax are sister groups to one another was explicitly rejected by an approximately unbiased ( AU) test. Furthermore, although different methods showed largely congruent results, we found that a supermatrix method using data partitioning with site-homogenous models potentially outperformed a supermatrix method using the CAT- GTR model and multispecies-coalescent approaches when the amount of missing data varies in a data set and when taxa susceptible to LBA are included in the analyses. [ABSTRACT FROM AUTHOR]

The high biodiversity found at cold seeps, despite elevated concentrations of methane and hydrogen sulfide, is attributed to multiple sources of habitat heterogeneity. In addition to geological and geochemical processes, biogenic habitats formed by large symbiont-bearing taxa, such as bivalves and siboglinid tubeworms, or by microbial mats drive the biodiversity of small-sized fauna. However, because these habitat-forming species also depend on geochemical gradients, the respective influence of abiotic and biotic factors in structuring associated macrofaunal communities is often unresolved. The giant pockmark Regab located at 3200 m depth on the Congo margin is characterized by different fluid-flow regimes, providing a mosaic of the most common biogenic habitats encountered at seeps: microbial mats, mussel beds, and vesicomyid clam beds; the latter being distributed along a gradient of environmental conditions from the center to the periphery of the pockmark. Here, we examined the structure of macrofaunal communities in biogenic habitats formed in soft sediment to (1) determine the influence of the habitats on the associated macrofaunal communities (inter-habitat comparison), (2) describe how macrofaunal communities vary among vesicomyid clam beds (intra-habitat comparison) and (3) assess the inter-annual variation in vesicomyid beds based on repeated sampling at a three-year interval. The highest densities were found in the microbial mat communities in intermediate fluid-flow areas, but they had low diversity — also observed in the sediment close to mussel beds. In contrast, vesicomyid beds harbored the highest diversity. The vesicomyid beds did not show a homogeneous macrofaunal community across sampled areas; instead, density and composition of macrofauna varied according to the location of the beds inside the pockmark. The clam bed sampled in the most active, central part of the pockmark resembled bacterial mat communities by the presence of highly sulfide-tolerant species living at the sediment surface, along with vesicomyid juveniles. This similarity suggests a gradual change in community composition from mats to clam beds. Inter-annual comparisons of the different clam beds highlighted that the most active central site had a more variable community than its peripheral counterparts. Finally, a rapid shift in community structure, particularly in polychaete families, in experimentally reduced oxygen concentrations in the central part of Regab, suggests that high beta-diversity communities can withstand intense variation in geochemical conditions. These community dynamics are likely related to the diversity and to the plasticity of the vesicomyids themselves, because they can cope with high spatial and temporal environmental variability at a very local scale. [ABSTRACT FROM AUTHOR]

A review of the taxonomy and distribution of vestimentiferan tubeworms has been performed. The subfamily Vestimentifera comprises three infrafamilies: Lamellibrachiinae, Escarpiinae, and Tevniinae. The complete descriptions and illustrations of 19 vestimentiferan species known to date are given. Comparative tables of the morphological characteristics of all vestimentiferan genera have been compiled. Lamellibrachiinae appear to be the most eurybathic group, representatives of which inhabit depths of 82-3200 m. Most representatives of Tevniinae reside deeper than 1500 m (except A. spiralis, which can be found at a depth of 750 m). Tevniinae live exclusively on the rocky substrate of hydrothermal vents. Lamellibrachiinae and Escarpiinae inhabit both soft and rocky substrates of cold seeps and the periphery of hydrothermal vents. Tevniinae occur only in the hydrothermal vents of the Pacific Ocean. Escarpiinae are found in the Pacific and Atlantic oceans. Lamellibrachiinae is the most widespread group that inhabits the Pacific and Atlantic oceans, including the Mediterranean Sea. The hypothesis on the Pacific origin on vestimentiferan tubeworms has been discussed. The eurybathic Lamellibrachiinae and Escarpiinae penetrated into the Atlantic Ocean through shallow-water basins of the Tethys Ocean and channels in the place of Mesoamerica, while the deep-sea Tevniinae were not able to do that. [ABSTRACT FROM AUTHOR]

Collections of Frenulata made by the RV Professor Logachev in the Gulf of Cadiz in 2006 contain two new species, one belonging to the genus Spirobrachia, and another that was assigned to a new genus. Spirobrachia tripeira n. sp. is the first record of the genus in the North Atlantic Ocean; it has a very stiff, straight, orange tube; its tentacles have pinnules and are arranged in a spiral crown without a lophophore. Bobmarleya gadensis n. gen. et n. sp. is characterised by an unusually long tentacular crown composed of about 40 free tentacles. It shares many characteristics with the genus Oligobrachia but the large number and extreme length of the tentacles and a combination of other characters justify the designation of a new genus. The specimens of Lamellisabella denticulata Southward, 1978 collected during the M.S. Merian 03/01 cruise provide the first record of this species in the Gulf of Cadiz.

Most members of Siboglinidae (Annelida) harbor endosymbiotic bacteria that allow them to thrive in extreme environments such as hydrothermal vents, methane seeps, and whale bones. These symbioses are enabled by specialized hemoglobins (Hbs) that are able to bind hydrogen sulfide for transportation to their chemosynthetic endosymbionts. Sulfur-binding capabilities are hypothesized to be due to cysteine residues at key positions in both vascular and coelomic Hbs, especially in the A2 and B2 chains. Members of the genus Osedax, which live on whale bones, do not have chemosynthetic endosymbionts, but instead harbor heterotrophic bacteria capable of breaking down complex organic compounds. Although sulfur-binding capabilities are important in other siboglinids, we questioned whether Osedax retained these cysteine residues and the potential ability to bind hydrogen sulfide. To answer these questions, we used high-throughput DNA sequencing to isolate and analyze Hb sequences from 8 siboglinid lineages. For Osedax mucofloris, we recovered three (A1, A2, and B1) Hb chains, but the B2 chain was not identified. Hb sequences from gene subfamilies A2 and B2 were translated and aligned to determine conservation of cysteine residues at previously identified key positions. Hb linker sequences were also compared to determine similarity between Osedax and siboglinids/sulfur-tolerant annelids. For O. mucofloris, our results found conserved cysteines within the Hb A2 chain. This finding suggests that Hb in O. mucofloris has retained some capacity to bind hydrogen sulfide, likely due to the need to detoxify this chemical compound that is abundantly produced within whale bones. [ABSTRACT FROM AUTHOR]

Background: Bone-devouring Osedax worms were described over a decade ago from deep-sea whale falls. The gutless females (and in one species also the males) have a unique root system that penetrates the bone and nourishes them via endosymbiotic bacteria. Emerging from the bone is a cylindrical trunk, which is enclosed in a transparent tube, that generally gives rise to a plume of four palps (or tentacles). In most Osedax species, dwarf males gather in harems along the female's trunk and the nervous system of these microscopic forms has been described in detail. Here, the nervous system of bone-eating Osedax forms are described for the first time, allowing for hypotheses on how the abberant ventral brain and nervous system of Siboglinidae may have evolved from a ganglionated nervous system with a dorsal brain, as seen in most extant annelids. Results: The intraepidermal nervous systems of four female Osedax spp. and the bone-eating O. priapus male were reconstructed in detail by a combination of immunocytochemistry, CLSM, histology and TEM. They all showed a simple nervous system composed of an anterior ventral brain, connected with anteriorly directed paired palp and gonoduct nerves, and four main pairs of posteriorly directed longitudinal nerves (2 ventral, 2 ventrolateral, 2 sets of dorso-lateral, 2 dorsal). Transverse peripheral nerves surround the trunk, ovisac and root system. The nervous system of Osedax resembles that of other siboglinids, though possibly presenting additional lateral and dorsal longitudinal nerves. It differs from most Sedentaria in the presence of an intraepidermal ventral brain, rather than a subepidermal dorsal brain, and by having an intraepidermal nerve cord with several plexi and up to three main commissures along the elongated trunk, which may comprise two indistinct segments. Conclusions: Osedax shows closer neuroarchitectural resemblance to Vestimentifera + Sclerolinum (= Monilifera) than to Frenulata. The intraepidermal nervous system with widely separated nerve cords, double brain commissures, double palp nerves and other traits found in Osedax can all be traced to represent ancestral states of Siboglinidae. A broader comparison of the nervous system and body regions across Osedax and other siboglinids allows for a reinterpretation of the anterior body region in the group. [ABSTRACT FROM AUTHOR]

Background: Sclerolinum (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. Results: Our 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. Conclusions: These 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. [ABSTRACT FROM AUTHOR]