Search

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.

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., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Author(s). Published by Elsevier Inc. All rights reserved.)

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., (© 2023. Pleiades Publishing, Ltd.)

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., (© 2023. Pleiades Publishing, Ltd.)

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., (© 2023. Pleiades Publishing, Ltd.)

The article describes the parameters of maintaining the gutless symbiotrophic annelid Siboglinum fiordicum in laboratory conditions outside the marine environment for 64 days., (© 2022. The Author(s).)

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., (© 2022. The Author(s).)

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., (© 2022. Pleiades Publishing, Ltd.)

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., (© 2022. Pleiades Publishing, Ltd.)

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., (© 2021. Pleiades Publishing, Ltd.)

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.

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]

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]

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.

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]

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]

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]

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]

We describe a broad zone of intergradation between genetically differentiated, northern and southern lineages of the hydrothermal vent tubeworm, Tevnia jerichonana . DNA sequences from four genes, nuclear HSP and ATPsα and mitochondrial COI and Cytb were examined in samples from eastern Pacific vent localities between 13°N and 38°S latitude. Allelic frequencies at these loci exhibited concordant latitudinal clines, and genetic differentiation (pairwise Φ ST 's) increased with geographical distances between sample localities. Though this pattern of differentiation suggested isolation-by-distance (IBD), it appeared to result from hierarchical population structure. Genotypic assignment tests identified two population clusters comprised of samples from the northern East Pacific Rise (NEPR: 9–13°N) and an extension of the Pacific-Antarctic Ridge (PAR: 31–32°S) with a zone of intergradation along the southern East Pacific Rise (SEPR: 7–17°S). The overall degrees of DNA sequence divergence between the NEPR and PAR populations were slight and not indicative of lengthy isolation. Bayesian assignment methods suggested that the SEPR populations constitute intergrades that connect the NEPR and PAR populations. Though it typically is difficult to distinguish between primary and secondary intergradation, our results were consistent with parallel studies of vent-restricted species that suggest a high degree of demographic instability along the superfast-spreading SEPR axis. Frequent local extinctions and immigration from NEPR and PAR refugia probably shaped the observed pattern of intergradation. [ABSTRACT FROM AUTHOR]

The article discusses research on the use of teleost bones and calcified shark cartilage to test the hypothesis of whether marine annelid worm Osedax species could obtain nutrition from non-mammalian bones. Experimental details which include the deployment of traps with bone and cartilage samples, identification of Osedax specimens, and examination of gene sequences are reported. It was observed that Osedax females have the ability to produce eggs and survive through teleost bone consumption.

Annelida, the ringed worms, is a highly diverse animal phylum that includes more than 15,000 described species and constitutes the dominant benthic macrofauna from the intertidal zone down to the deep sea. A robust annelid phylogeny would shape our understanding of animal body-plan evolution and shed light on the bilaterian ground pattern. Traditionally, Annelida has been split into two major groups: Clitellata (earthworms and leeches) and polychaetes (bristle worms), but recent evidence suggests that other taxa that were once considered to be separate phyla (Sipuncula, Echiura and Siboglinidae (also known as Pogonophora)) should be included in Annelida. However, the deep-level evolutionary relationships of Annelida are still poorly understood, and a robust reconstruction of annelid evolutionary history is needed. Here we show that phylogenomic analyses of 34 annelid taxa, using 47,953 amino acid positions, recovered a well-supported phylogeny with strong support for major splits. Our results recover chaetopterids, myzostomids and sipunculids in the basal part of the tree, although the position of Myzostomida remains uncertain owing to its long branch. The remaining taxa are split into two clades: Errantia (which includes the model annelid Platynereis), and Sedentaria (which includes Clitellata). Ancestral character trait reconstructions indicate that these clades show adaptation to either an errant or a sedentary lifestyle, with alteration of accompanying morphological traits such as peristaltic movement, parapodia and sensory perception. Finally, life history characters in Annelida seem to be phylogenetically informative. [ABSTRACT FROM AUTHOR]

The article presents author's comments on the ecology and evolution of siboglinid tubeworms. It mentions that siboglinid are annelids that are the member of the chemosyenthtic community. It offers information on four lineages in Siboglinidae including, Frenulata, Vestimentifera and Osedax. It mentions that Osedax, new radiation of siboglinids, have been discovered on whale bones. It focuses on the symbiotic relationship between siboglinids and their endosymbiotic bacteria. It mentions that taxonomy and systematics played an important role in the elevation of discoveries.

Abstract: Siboglinids are symbiotic polychete annelids having hemoglobins as essential oxygen- and sulfide-carriers for their endosymbiotic bacteria. We analyzed the structure of the hemoglobins from two species of siboglinids: the monilifera Sclerolinum contortum and the frenulata Oligobrachia webbi (i.e. haakonmosbiensis) from Norwegian cold seeps. Measured by Multi-Angle Laser Light Scattering (MALLS), Sclerolinum shows a 3190±50kDa hexagonal bilayer hemoglobin (HBL-Hb) and a 461±46kDa ring-Hb, just as vestimentifera, whereas Oligobrachia has a 409±3.7kDa ring-Hb only. Electrospray Ionization-Mass Spectrometry (ESI-MS) showed Sclerolinum HBL-Hb composed of seven monomeric globins (15–16kDa), three disulfide-bonded globin heterodimers and three linkers. The heterodimers always contain globin-b (15814.4±1.5Da). Sclerolinum ring-Hb is composed of globins and dimers with identical masses as its HBL-Hb, but lacks linkers. Oligobrachia ring-Hb has three globin monomers (14–15kDa) only, with no disulfide-bonded dimers. Comparison of Sclerolinum hemoglobins between Storegga and Haakon Mosby Mud Volcano, using the normalized height of deconvoluted ESI-MS peaks, shows differences in globin monomers abundances that could reflect genetic differences or differential gene expression between distinct seep populations. The discovery of HBL-Hb in Sclerolinum is a new element supporting the hypothesis of monilifera being phylogenetically more closely related to vestimentifera, than to frenulata. [Copyright &y& Elsevier]

We report observations on spawning and early development in bone-eating worms of the genus Osedax. Individual females of Osedax rubiplumus were observed at 1820 m depth freely spawning hundreds of oocytes, and females of an undescribed species, Osedax “orange collar”, were observed spawning in laboratory aquaria. Cytological and molecular analysis of the spawned oocytes of two Osedax species revealed no evidence for the bacterial endosymbionts that the female worms require for their nutrition, suggesting that the bacteria must be acquired later from the environment, as they are in other siboglinids. Individual O. “orange collar” females released an average of 335 (±130) eggs per day, but the number of oocytes spawned per day varied greatly, suggesting that not all the females spawned daily. Fertilization rates of the spawned oocytes varied from 0 to 100%, though most females showed nearly 100% fertilization rates. Oocytes spawned in the laboratory at 4–6°C were negatively buoyant. If fertilized, these oocytes extruded polar bodies and then after at least four hours cleaved unequally. Subsequent cleavages occurred in a spiral pattern at roughly 2-h intervals, resulting in free-swimming trochophore larvae after 24 h. These lecithotrophic trochophores swam for 9–16 days before settling with several hooked chaetae, similar to those of dwarf Osedax males. The larval life span of the Osedax species studied in the laboratory appears to be shorter than in closely related Vestimentifera. Osedax rubiplumus, on the other hand, has much larger oocytes and so may have greater dispersal potential than these other Osedax species. The high fecundity and apparently continuous reproduction of Osedax boneworms permits the opportunistic exploitation of sunken vertebrate bones. [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. [ABSTRACT FROM AUTHOR]

Extreme male dwarfism occurs in Osedax (Annelida: Siboglinidae), marine worms with sessile females that bore into submerged bones. Osedax are hypothesized to use environmental sex determination, in which undifferentiated larvae that settle on bones develop as females, and subsequent larvae that settle on females transform into dwarf males. This study addresses several hypotheses regarding possible recruitment sources for the males: (i) common larval pool— males and females are sampled from a common pool of larvae; (ii) neighbourhood— males are supplied by a limited number of neighbouring females; and (iii) arrhenotoky— males are primarily the sons of host females. Osedax rubiplumus were sampled from submerged whalebones located at 1820-m and 2893-m depths in Monterey Bay, California. Immature females typically did not host males, but mature females maintained male ‘harems’ that grew exponentially in the number of males as female size increased. Allozyme analysis of the females revealed binomial proportions of nuclear genotypes, an indication of random sexual mating. Analysis of mitochondrial DNA sequences from the male harems and their host females allowed us to reject the arrhenotoky and neighbourhood hypotheses for male recruitment. No significant partitioning of mitochondrial diversity existed between the male and female sexes, or between subsamples of worms collected at different depths or during different years (2002–2007). Mitochondrial sequence diversity was very high in these worms, suggesting that as many as 106 females contributed to a common larval pool from which the two sexes were randomly drawn. [ABSTRACT FROM AUTHOR]

Abstract: The small frenulate pogonophores (Annelida: Pogonophora a.k.a. Siboglinidae) typically inhabit muddy sediments on the continental slope, although a few species occur near hydrothermal vents and cold seeps. We present data on the distribution and habitat characteristics of several species on the European continental shelf and slope from 48°N to 75°N and show how the animals interact with the chemistry of the sediments. The environments inhabited include: shallow (30m), organic-rich, fjord sediments; slope sediments (1000–2200m) and methane seeps at 330m depth. All the species studied obtain nutrition from endosymbiotic bacteria. They take up reduced sulphur species, or in one case, methane, through the posterior parts of their tubes buried in the anoxic sediment. We conclude that most species undertake sulphide ‘mining’, a mechanism previously demonstrated in the bivalves Lucinoma borealis and Thyasira sarsi. These pogonophores participate in the sulphur cycle and effectively lower the sulphide content of the sediments. Our results show that the abundance of frenulate pogonophores increases with increasing sedimentation and with decreasing abundance of other benthos, particularly bioturbating organisms. The maximum sustainable carrying capacity of non-seep sediments for frenulate pogonophores is limited by the rate of sulphate reduction. [Copyright &y& Elsevier]

After the deployment of several whale carcasses in Monterey Bay, California, a time-series analysis revealed the presence of a new species of Osedax, a genus of bone-eating siboglinid annelids. That species is described here as Osedax roseus n. sp. It is the fifth species described since the erection of this genus and, like its congeners, uses a ramifying network of "roots" to house symbiotic bacteria. In less than 2 months, Osedax roseus n. sp. colonized the exposed bones of a whale carcass deposited at 1018-m depth, and many of the females were fecund in about 3 months post-deployment. As with other Osedax spp., the females have dwarf males in their tube lumens. The males accrue over time until the sex ratio is markedly male-biased. This pattern of initial female settlement followed by gradual male accumulation is consistent with the hypothesis that male sex may be environmentally determined in Osedax. Of the previously described species in this genus, Osedax roseus n. sp. is most similar to O. rubiplumus, but it has several anatomical differences, as well as much smaller females, dwarf males, and eggs. Osedax roseus n. sp. is markedly divergent (minimally 16.6%) for mitochondrial cytochrome oxidase subunit I (mtCOI) sequences from any other Osedax species. [ABSTRACT FROM AUTHOR]

Pogonophora, also known as Siboglinidae, are tube-dwelling marine annelids. They rely on endosymbiotic chemoautotrophic bacteria for nutrition and their anatomy and physiology are adapted to their need to obtain both oxygen and reduced sulphur compounds. Frenulate pogonophores are generally long and slender, sediment-living tubeworms; vestimentiferans are stouter, inhabitants of hydrothermal vents and cool seeps; and moniliferans or sclerolinids are very slender inhabitants of decaying wood and sulphidic sediments. The anatomy and ultrastructure of the three groups are compared and recent publications are reviewed. Annelid characters are the presence of chaetae and septa, concentrated at the hind end. The adaptations to a specialised way of life include, in particular, the chitinous tube; the anterior appendages that function as gills; the internal tissue called the trophosome, where the endosymbiotic bacteria live; and the blood vascular system that transports oxygen, sulphide and carbon dioxide to the trophosome. [ABSTRACT FROM AUTHOR]

We assess the phylogenetic position of Siboglinidae (previously known as the phyla Pogonophora and Vestimentifera, but now referred to Annelida) in parsimony analyses of 1100 bp from 18S rRNA, 320 bp from the D1 region of 28S rRNA, and 107 morphological characters, totaling 667 parsimony informative characters. The 34 terminal taxa, apart from six siboglinids, include polychaete members of Sabellida, Terbelliformia, Cirratuliformia and Spionida, plus two Aciculata polychaetes as outgroups. Our results contradict most recent hypotheses in showing a sistergroup relationship between Siboglinidae and Oweniidae, and in that the latter taxon is not a member of Sabellida. Furthermore, our results indicate that Sabellariidae is not closely related to Sabellida, that Serpulidae may be nested within Sabellidae, and that Alvinellidae is nested within Ampharetidae.© The Willi Hennig Society 2004. [ABSTRACT FROM AUTHOR]

We describe a new genus, Osedax, and two new species of annelids with females that consume the bones of dead whales via ramifying roots. Molecular and morphological evidence revealed that Osedax belongs to the Siboglinidae, which includes pogonophoran and vestimentiferan worms from deep-sea vents, seeps, and anoxic basins. Osedax has skewed sex ratios with numerous dwarf (paedomorphic) males that live in the tubes of females. DMA sequences reveal that the two Osedax species diverged about 42 million years ago and currently maintain large populations ranging from 10[sup 5] to 10[sup 6] adult females. [ABSTRACT FROM AUTHOR]

Ultrastructural characteristics of the epidermis of 5 deep-sea vestimentiferan tube worms and an orbiniid worm were similar to those described from other organisms inhabiting sulfidic environments. The integument was composed of a simple or pseudostratified layer of columnar or cuboidal cells, covered by a cuticle of varying thickness, and rested on an extra-cellular matrix. Unusual mitochondrial morphology was observed in the peripheral region of the epidermis, characterized by an electron-dense matrix and granules. The abnormal size, shape, and reduced array of cristae in these mitochondria may have resulted from environmental stress. Mitochondria in the inner epidermal layers, where they are more protected from sulfide exposure, displayed normal morphology. The seep vestimentiferans (Seepiophila jonesi and Lamellibrachia cf. luymesi) exhibited numerous electron-dense organelles, similar in morphology to cytolysosomes and previously described as sulfide oxidizing bodies, while in the 3 vent vestimentiferans (Riftia pachyptila, Tevnia jerichonana, and Oasisia alvinae) and the seep or- biniid Methanoaricia dendrobranchiata, fewer of these organelles were observed. Energy dispersive x-ray microanalysis of these electron-dense organelles indicated the presence of sulfur, iron, zinc, and copper, as well as lesser amounts of other elements. We propose that these epidermal cytolysosomes are morphologically similar to previously described sulfide oxidizing bodies that have been hypothesized to play a role in maintaining aerobically poised animal metabolism in sulfide-enriched habitats. [ABSTRACT FROM AUTHOR]

Abstract The phylogenetic position of Annelida as well as its ingroup relationships are a matter of ongoing debate. A molecular phylogenetic study of sedentary polychaete relationships was conducted based on 70 sequences of 18S rRNA, including unpublished sequences of 18 polychaete species. The data set was analysed with maximum parsimony and maximum likelihood methods. Clade robustness was estimated by parsimony-bootstrapping and jackknifing, decay index, and clade support, as well as a posteriori probability tests using Bayesian inference. Irrespective of the applied method, some traditional sedentary polychaete taxa, such as Cirratulidae, Opheliidae, Orbiniidae, Siboglinidae and Spionidae, were recovered by our phylogenetic reconstruction. A close relationship between Orbiniidae and Questa received a particularly strong support. Echiura appears to be a polychaete ingroup taxon which is closely related to Dasybranchus (Capitellidae). As in previous molecular analyses, no support was found for the monophyly of Annelida nor for that of Polychaeta. However, we suggest that an increase in taxon sampling may yield additional resolution in the reconstruction of polychaete ingroup phylogeny, although the difficulties in reconstructing the basal phylogenetic relationships within Annelida may be due to their rapid radiation. [ABSTRACT FROM AUTHOR]

Vestimentifera, formerly considered a phylum, are here included in the annelid clade Siboglinidae which also encompasses Frenulata and Sclerolinum . All Siboglinidae inhabit reducing habitats, mostly in the deep sea. Vestimentifera are known from hydrothermal vents and cold seeps. Cladistic analyses of vestimentiferan relationships are performed on three levels: (1) among the vestimentiferan species, (2) among the reconstructed ancestral vestimentiferan and other siboglinids and (3) on the level of the families included in the annelidan clade Sabellida. The monophyly of vestimentiferans is confirmed in all analyses. A group of exclusively vent-inhabiting species forms a derived monophyletic clade. The sister group to the vent clade is the Escarpia complex. Lamellibrachia appears to be paraphyletic. Except for the paraphyly of Lamellibrachia , the reconstructed pattern agrees with the molecular phylogeny based on cytochrome c oxidase subunit I. Ancient ridge systems can be invoked to explain modern day geographical distributions. The Pacific Kula Ridge that spanned the Pacific in an east–west direction during the Early Tertiary, may have been a pathway for the ancestor of the vent clade to reach the eastern Pacific. The biogeography is consistent with the recent divergence of Vestimentifera as inferred from molecular data. The reconstructed phylogeny of the Siboglinidae supports the monophyly of the Frenulata and within those, the Thecanephria and Athecanephria. In contrast to molecular and other morphological analyses, Sclerolinum appears as the sister group to the Frenulata. The family level analysis supports the sister group relationship of the Siboglinidae to a clade formed by Sabellariidae, Sabellidae and Serpulidae. Hypothesized homologies of the vestimentiferan obturaculum and vestimentum to structures in related taxa need further investigation. [ABSTRACT FROM AUTHOR]