Tube-dwelling Polychaetes Research Articles

Ultrastructure of the Jurassic serpulid tubes-phylogenetic and paleoecological implications.

The ultrastructural diversity of the Middle and Late Jurassic serpulid tubes from the Polish Basin has been investigated. The inspection of 12 taxa representing the two major serpulid clades allowed for the identification of three ultrastructure types-irregularly oriented prismatic structure (IOP), spherulitic prismatic structure (SPHP), and simple prismatic structure (SP). Six of the studied species are single-layered and six species possess two distinct layers. Ultrastructural diversity corresponds to certain serpulid clades. The members of Filograninae have single-layered tube walls composed of possibly plesiomorphic, irregularly oriented prismatic structure (IOP). Two-layered tubes occur solely within the clade Serpulinae, where the external, denser layer is built of either the ordered spherulitic (SPHP) or simple prismatic microstructure (SP), and the internal layer is composed of irregularly oriented prismatic structure (IOP). Apart from phylogenetic signals provided by the tube ultrastructure, it can be used in analyzing paleoecological aspects of tube-dwelling polychaetes. Compared to the more primitive, irregularly oriented microstructures of Filograninae, the regularly oriented microstructures of Serpulinae need a higher level of biological control over biomineralization. The advent of the dense outer protective layer (DOL) in serpulids, as well as the general increase in ultrastructure diversity, was likely a result of the evolutionary importance of the tubes for serpulids. Such diversity of the tube ultrastructural fabrics allowed for maximizing functionality by utilizing a variety of morphogenetic programs. The biomineralization system of serpulids remains more complex compared to other tube-dwelling polychaetes. Physiologically more expensive tube formation allows for mechanical strengthening of the tube by building robust, strongly ornamented tubes and firm attachment to the substrate. Contrary to sabellids, which perform a fugitive strategy, an increased tube durability allows serpulids a competitive advantage over other encrusters.

Tectorotularia hexagona (Polychaeta, Serpulidae) co-existing with Rhynchostreon suborbiculatum (Bivalvia, Gryphaeidae) in a river-dominated marginal marine environment of Cenomanian–Turonian age in Slovakia: An example of Late Cretaceous amensalism or competition?

The mutual relationship and co-occurrence of the tube-dwelling polychaete Tectorotularia hexagona and the oyster Rhynchostreon suborbiculatum in an instance of fluctuating marginal marine environment, represented by the Orlové Sandstone in the Western Carpathians (Pieniny Klippen Belt), is recorded. As a consequence of climate change during the Cenomanian and early Turonian, changes over time in key ecological factors (e.g., decrease in freshwater inflow and increase in temperature and water mass salinity) led to critical trophic alterations in the marginal marine system studied. The environmental change from polyhaline/eutrophic to euhaline/lower nutrient conditions led to a reduction in the pioneer palaeopopulation of R. suborbiculatum, and Tectorotularia hexagona and other stenohaline marine recliners took over the ecological niches originally occupied by the oyster. In this respect, the relationship between T. hexagona and R. suborbiculatum may be considered a Late Cretaceous example of competition between two groups of sessile-benthic recliners. In the present work, two different tube morphologies of T. hexagona from Hôrka are described, and the tube microstructure of this species is documented for the first time. In addition, the material from Hôrka is compared with that from the type locality, Essen in Germany, and ‘Hamulus’ hexagonus and Tectorotularia ‘westfalica’ are considered to constitute one and the same species. The wider ecological and systematic context of this serpulid species is discussed as well.

The Upper Permian tubular fossils from South China and their possible affinity to sabellid polychaetes

ABSTRACT This study analyses intriguing tubular fossils derived from the Upper Permian deposits of southern China. The fossils’ structure is diagenetically altered by silicification precluding an unambiguous systematic assignment. However, the general morphology and tube architecture strongly imply a relationship with tube-dwelling organisms of different affinity such as tentaculitoids and tube-dwelling polychaetes. Due to the simple morphology of the tubes lacking any ornamentation, as well as the encrustation mode of some individuals, the investigated specimens most likely belong to early sabellids. Although calcareous sabellids persisted since the Middle Permian, their distribution and abundance during the Permian were confined to a single occurrence. If the fossils studied indeed represent sabellids, the global range and abundance of this group during the late Palaeozoic was likely more extensive than currently assumed.

First screening of bacteria assemblages associated with the marine polychaete Melinna palmata Grube, 1870 and adjacent sediments

Bacteria associated with marine invertebrate play a fundamental role in the biology, ecology, development and evolution of their hosts. Although many studies have been focused on the microbial populations of benthic and pelagic habitats, little is known about bacteria colonizing tube-dwelling polychaete. In this context, the current study provided the first characterization of the Melinna palmata Grube, 1870 microbiome based on Illumina sequencing of 16S rRNA gene of the polychaete tissue and proximate sediments collected from the Black Sea, Romania, along a 24.2 m – 45.4 m depth-gradient. The diversity, taxonomic composition and deduced functional profile of the tissue and sediments associated bacterial communities were compared and analyzed in relation with the environmental parameters. This polychaete harbored a distinct bacterial assemblage as compared to their sediments and independent on the depth of their habitat, including 8 phyla in tissues dominated by Proteobacteria, and 12 phyla in sediments majorly represented by Actinobacteriota, respectively. At order level, Synechococcales, Rhodobacterales and Actinomarinales were highly represented in the M. palmata microbiome, while Microtrichales, Anaerolineales and Caldilineales were mostly found in sediments. A significant correlation was observed between Cyanobacteria taxa and the dissolved oxygen concentrations in shallow waters impacted by the Danube inputs. Meanwhile, this phylum showed a positive correlation with Planctomycetota colonizing the invertebrate tissues, and a negative one with Actinobacteriota and Chloroflexi found in sediments. The deduced functional profile of these bacterial assemblages suggested the prevalence of the amino acid and carbohydrate metabolism for both analyzed matrices. This pioneering report on the M. palmata microbiome highlighted the environment contribution to bacterial species enrichment of the polychaete, and provided a glimpse on the putative role of microbial communities associated with this marine organism.

Deep Aggregations of the Polychaete Amage adspersa (Grube, 1863) in the Ionian Sea (Central Mediterranean Sea) as Revealed via ROV Observations

Many sessile and tube-dwelling polychaetes can act as ecosystem engineers, influencing the physical–chemical and biological characteristics of their habitats, increasing structural complexity. Thus, they are considered structuring species. In summer of 2021, in southern Sicily (Ionian Sea), benthic assemblages dominated by Ampharetidae Amage adspersa were discovered via an ROV survey at a depth range between 166 and 236 m on muddy horizontal seafloor. Large aggregations of this species (up to 297.2 tubes m−2), whose tubes are formed from Posidonia oceanica debris, occurred alternately with tube-free areas. The area was characterized by the sporadic presence of vulnerable sea pens Funiculina quadrangularis (up to 0.08 col. m−2) and Virgularia mirabilis (up to 0.16 col. m−2), and it was possible to detect signs of trawling as well the presence of marine litter (up to 24.0 items 100 m−2). The habitat description, distribution, and density of the tubes of A. adspersa were assessed via imaging analysis. In addition, morphological diagnostic analyses were carried out on some sampled specimens and on their tubes. The acquired data shed new light on how polychaetes can exploit the dead tissues of P. oceanica, contributing to highlight interactions between benthic fauna and seagrass detritus in the marine environment and their ecological role in enhancing the spatial heterogeneity of soft areas of the Mediterranean seafloor.

Assessment of the Sabellaria alveolata reefs’ structural features along the Southern coast of Sicily (Strait of Sicily, Mediterranean Sea)

The honeycomb worm Sabellaria alveolata is a gregarious tube-dwelling polychaete that builds remarkable biogenic reefs in marine coastal waters. Sabellaria alveolata reefs are considered valuable marine habitats requiring protection measures for their conservation, as they play a key role in the functioning of coastal ecosystems. Sabellarid reefs are extensively developed along the Atlantic coasts of Europe and reported for the Mediterranean Sea and the Italian coasts, where large reefs have been recorded in several localities. Fragmentary information is available on their health status, Sabellaria reefs thus being listed as “Data Deficient” in the Red List of Marine Habitats. To fill this knowledge gap, this study focused on the analysis of the structure of three reefs found along the southern coast of Sicily. In particular, we aimed to assess their phases with respect to the natural cycle that characterizes the sabellarid reefs. Reef features were analyzed both on the macroscale, based on the bioconstruction size (diameter and thickness) and degree of fragmentation, and on the microscale, based on the measurement of worm density, opercular length and sand porch presence. This study reveals relevant differences among reefs of the studied locations. These differences we attributeto the temporal shift linked to the natural reef phases, albeit further analyses are needed to understand the possible effect of natural and anthropogenic sources of variation on the Southern Sicilian reefs. In conclusion, Sabellaria reefs are a unique and persistent habitat along the Sicilian coast requiring proper management and conservation measures.

Middle and Late Jurassic tube-dwelling polychaetes from the Polish Basin: diversity, palaeoecology and comparisons with other assemblages

Middle and Late Jurassic tube-dwelling polychaetes from the Polish Basin: diversity, palaeoecology and comparisons with other assemblages

Sediment macrofaunal response to the diel oxygen cycle

Infauna exhibit a range of behavioral responses to declining dissolved oxygen concentrations that affect their burrowing and feeding behaviors. Diel oxygen cycles, common in shallow coastal areas, may drive changes in faunal behavior that affect sediment mixing. In this laboratory study we exposed 3 species, the burrowing ophiuroid Hemipholis cordifera, the tube-dwelling polychaete Owenia fusiformis, and the burrowing clam Ameritella versicolor, to 60 h of diel cycling dissolved oxygen in the overlying water, with oxygen concentration varying between 2 and 7 mg l-1. We observed the study organisms’ behaviors and evaluated their sediment mixing activity using luminophores applied to the sediment surface. We found that sediment mixing activity of all 3 taxa, measured as percent decrease in luminophore coverage, varied proportionally with dissolved oxygen concentration during the diel cycle. Observations of animal behavior did not reveal a diel pattern, though this was likely due to the temporal and spatial scale of observations. Our results also indicated that diel cycling oxygen may change faunal effects on the sediment in ways that only emerge after more than a single cycle. Measuring sediment mixing in sustained full oxygen saturation may produce misleading estimates over time, and future research should investigate how faunal responses to short-term variability can scale to have longer-term effects.

Sclerobionts on tubes of the serpulid Pyrgopolon (Pyrgopolon) deforme (Lamarck, 1818) from the upper Cenomanian of Le Mans region, France

Serpulid polychaetes are described as common encrusting organisms inhabiting various substrates, but very few studies deal with tube-dwelling polychaetes as substrates for encrusters and borers. Here we focus on Pyrgopolon (Pyrgopolon) deforme, a serpulid species common in the Cenomanian of Le Mans region which acted as small solid benthic islands for colonization by invertebrates on a soft sandy/marly bottom. A relatively rich assemblage of 88 individuals was studied surficially, 15 specimens were imaged with CT, and five specimens were prepared as vacuum epoxy casts. Borings found in the tubes show relatively low diversity; nevertheless, several different, recurring shapes were recognized. Borings of the ichnogenus Rogerella are among the best preserved. The examined tubes represent the second known case of interaction between boring barnacles (Rogerella tracemakers) and serpulid worms. Short shafts perpendicular to tube surfaces are attributable to Trypanites isp. Longer, irregularly meandering tunnels resemble another form of Trypanites isp., but usually display more than one opening, suggesting Maeandropolydora. Another boring is a drop-shaped chamber with a relatively large aperture and several narrower side openings. They can be preliminarily assigned to unicamerate entobians. Among sclerozoans, encrusting oysters and cheilostome and cyclostome bryozoan colonies are the most abundant groups. Other encrusters such as serpulid and sabellid worms and foraminifers are less common, infesting fewer than 10% of tubes. Due to the high density of infestation, random distribution of boreholes and lack of signs of repair of the penetrated tube walls by the host organism, post-mortem infestation of Pyrgopolon (P.) deforme is suggested.

Assessment of serpulid-hydroid association through the Jurassic: A case study from the Polish Basin.

The coexistence of sessile, tube-dwelling polychaetes (serpulids) and hydroids, has been investigated. Serpulid tubes bearing traces after hydroids are derived from different stratigraphic intervals spanning the Middle and Upper Jurassic, the rocks of which represent the diverse paleoenvironments of the Polish Basin. Although fossil colonial hydroids classified under the species Protulophila gestroi are a commonly occurring symbiont of these polychaetes during the Late Cretaceous and Cenozoic, they seem to be significantly less frequent during the Jurassic and limited to specific paleoenvironments. The hydroids described here are represented by traces after a thin stolonal network with elongated polyp chambers that open to the outer polychaete tube’s surface with small, more or less subcircular apertures. Small chimney-like bulges around openings are an effect of the incorporation of the organism by in vivo embedment (bioclaustration) within the outer layers of the calcareous tube of the serpulid host. Considering the rich collection of well-preserved serpulid tubes (>3000 specimens), the frequency of bioclaustrated hydroids is very low, with an infestation percentage of only 0.6% (20 cases). It has been noticed that only specimens of the genus Propomatoceros from the Upper Bajocian, Lower Bathonian, Middle Bathonian, and Callovian have been found infested. However, the majority of bioclaustrated hydroids (17 cases) have been recorded in the Middle Bathonian serpulid species Propomatoceros lumbricalis coming from a single sampled site. Representatives of other genera are not affected, which is congruent with previous reports indicating that Protulophila gestroi was strongly selective in the choice of its host. A presumably commensal relationship is compared with the recent symbiosis between the hydroids of the genus Proboscidactyla and certain genera of sabellid polychaetes.

Microplastic accumulation by tube-dwelling, suspension feeding polychaetes from the sediment surface: A case study from the Norwegian Continental Shelf

Sediment samples (0–1 cm) and tube-dwelling polychaetes from the Norwegian Continental Shelf and the Barents Sea were collected, including areas close to oil and gas installations and remote locations. Microplastics (≥45 μm) were found in quantifiable levels in 27 of 35 sediment samples, from 0.039 to 3.4 particles/gdw (dw = dry weight); and in 9 of 10 pooled polychaete samples, from 11 to 880 particles/gww (ww = wet weight). Concentrations were significantly higher in tube-dwelling polychaetes than sediments from the same locations (p<0.0097) by orders of magnitude. To quantify this factor increase in polychaetes, a Biota-Sediment Particle Enrichment Factor (BSPEF) is introduced, which ranged from 100 to 11000 gdw/gww (280–31000 gdw/gdw). Higher microplastic levels were observed in polychaete tube than in soft tissue (n=4). The feeding behavior and life cycle of tube-dwelling polychaetes could have an important influence on the transport, distribution and food-chain dynamics of microplastics on the seafloor.

Denitrification and the Role of Macrofauna Across Estuarine Gradients in Nutrient and Sediment Loading

To cope with increasing nitrogen loading to estuarine systems, the demand for removal via denitrification is rising. Understanding how the connections between biogeochemistry and ecology regulate denitrification rates along gradients of nutrient and sediment loading is necessary to predict ecosystem function. Previous studies have shown that denitrification rates are typically highest in muddy, nutrient-rich sediments and decrease in sandy, nutrient-poor sites. Denitrification rates were measured at four subtidal sites positioned from the upper to lower estuary. Site 1 was closest to the primary riverine nutrient supply with the highest suspended sediment and benthic mud content that decreased with distance downstream. Contrary to expectations, denitrification rates were lowest at the most upstream site (22.35 ± 13.34 μmol N2 m−2 h−1) and higher downstream (57.84 ± 5.72 μmol N2 m−2 h−1). While respiration, primary production, and sediment characteristics affected net denitrification rates and efficiency, results indicated that macrofaunal abundance (Site 1, 60.8 ± 7.3 individuals/core; Sites 2–4, 177.7 ± 10.8 individuals/core), primarily tube-dwelling polychaetes (Site 1, 0.5 ± 0.5 individuals/core; sites 2–4, 122.5 ± 8.0 individuals/core), played an important role. Their influence was highest in muddier sediments (median grain size < 85 μm) where an increase in pseudopolydorid abundance (0.5 ± 0.5 to 149.5 ± 13.4 individuals per core) resulted in a ~ 3-fold rise in denitrification rate (22.3 ± 13.3 to 62.24 ± 11.1 μmol N2 m−2 h−1). The linkage between macrofauna and denitrification demonstrates their role in maintaining ecosystem function and bolstering resilience in sites affected by sediment and nutrient pollution.

First record of Polyonyx loimicola Sankolli, 1965 (Crustacea, Decapoda, Anomura, Porcellanidae) from the Red Sea, Egypt

The first record of the porcellanid crab, Polyonyx loimicola Sankolli, 1965, from Ain-Sokhna, Suez Gulf, Egypt, the Red Sea, is provided far away from its known localities in India and Pakistan. The present specimens were found in association with one tube-dwelling polychaete species, Chaetopterus variopedatus (Renier, 1804), in soft sandy habitat. They agree well with the original description of P. loimicola in most of its diagnostic characters. Intraspecific variation is recognized in the number of ventral spines of the ambulatory propodi.

Visual evidence of reduced seafloor conditions and indications of a cold-seep ecosystem from the Hatton–Rockall basin (NE Atlantic)

High definition video from a towed camera system was used to describe the deep-sea benthic habitats within an elongate depression located at the western margin of Rockall Bank in the Hatton–Rockall Basin. At depths greater than 1190 m, an extensive area (10 km long by 1.5 km wide) of what appeared to be reduced sediments, bacterial mats and flocculent matter indicated possible cold-seep habitat. Plumes of sediment-rich fluid were observed alongside raised elongate features that gave topographic relief to the otherwise flat seafloor. In the deepest section of the depression (1215 m) dense flocculent matter was observed suspended in the water column, in places obscuring the seabed. Away from the bacterial mats, the habitat changed rapidly to sediments dominated by tube-dwelling polychaete worms and then to deep-sea sedimentary habitats more typical for the water depth (sponges and burrowing megafauna in areas of gentle slopes, and coral gardens on steeper slopes).

Further polyphyly of pinnotheroid crabs: the molecular phylogenetic position of the polychaete-associated Aphanodactylidae

Pea crabs of the superfamily Pinnotheroidea De Haan, 1833 are known for their obligate commensal relationships with other marine invertebrates. The concomitant specialisations and adaptations of pinnotheroids have resulted in superficially similar body forms that include a high degree of structural reduction. This has confounded interpretation of their phylogenetic position in the Brachyura and interrelationships within Pinnotheroidea, though all were nevertheless believed to be united by a monophyletic origin of obligate commensalism. The family Aphanodactylidae Ahyong &amp;amp; Ng, 2009 was proposed for a group of genera associated with tube-dwelling polychaetes formerly classified in Pinnotheridae, and provisionally retained in the Pinnotheroidea. We investigated the phylogenetic position of Aphanodactylidae using molecular data from three markers (mitochondrial 12S and 16S rRNAs, and nuclear histone H3) covering five of the 12 described aphanodactylid species and a total of 15 thoracotreme families. We found Aphanodactylidae to be monophyletic, but widely distant from Pinnotheridae and instead most closely related to Macrophthalmidae (Ocypodoidea) and Varunidae (Grapsoidea). Therefore, the family Aphanodactylidae is corroborated, but its placement in Pinnotheroidea is rejected. Instead, the phylogenetic position of Aphanodactylidae, as clearly distant from other pinnotheroids, demonstrates that obligate commensalism has evolved independently multiple times within Thoracotremata.

Reducing the data-deficiency of threatened European habitats: Spatial variation of sabellariid worm reefs and associated fauna in the Sicily Channel, Mediterranean Sea

Biogenic reefs, such as those produced by tube-dwelling polychaetes of the genus Sabellaria, are valuable marine habitats which are a focus of protection according to European legislation. The achievement of this goal is potentially hindered by the lack of essential empirical data, especially in the Mediterranean Sea. This study addresses some of the current knowledge gaps by quantifying and comparing multi-scale patterns of abundance and distribution of two habitat-forming species (Sabellaria alveolata and S. spinulosa) and their associated fauna along 190 km of coast on the Italian side of the Sicily Channel. While the abundance of the two sabellariids and the total number of associated taxa did not differ at any of the examined scales (from tens of centimetres to tens-100 of kilometres), the structure (composition in terms of both the identity and the relative abundance of constituting taxa) of the associated fauna and the abundance of several taxa (the polychaetes Eulalia ornata, Syllis pulvinata, S. garciai, Nereis splendida and Arabella iricolor, and the amphipods Apolochus neapolitanus, Tethylembos viguieri and Caprella acanthifera) varied among locations established ∼50–100 km apart. Syllis pulvinata also showed significant variation between sites (hundreds of metres apart), analogously to the other syllid polychaetes S. armillaris and S. gracilis, the nereidid polychaete Nereis rava, and the amphipod Gammaropsis ulrici. The largest variance of S. spinulosa, of the structure of the whole associated fauna and of 56% of taxa analysed individually occurred at the scale of replicates (metres apart), while that of the dominant bio-constructor S. alveolata and of 25% of taxa occurred at the scale of sites. The remaining 19% and the total richness of taxa showed the largest variance at the scale of locations. Present findings contribute to meet a crucial requirement of any future effective protection strategy, i.e., identifying relevant scales of variation to be included in protection schemes aiming at preserving representative samples not only of target habitats and organisms, but also of the processes driving such variability.

Structural and functional changes of soft-bottom ecosystems in northern fjords invaded by the red king crab (Paralithodes camtschaticus)

Abstract The red king crab invaded Norwegian coastal waters in the early 1990s after having been introduced from the northern Pacific to the Russian Barents Sea coast. The crab stock increased rapidly in NE northern Norway in the latter half of the 1990s, and since 2002 there has been a commercial fishery in the eastern invaded areas. The crab is an active predator on benthic fauna especially feeding in deep soft-bottom environments. The present study is a follow-up of previous studies (2007–09) to assess the effects of the king crab predation on soft bottom species composition, ecological functioning and sediment quality. Macroinfauna (> 1 mm) was investigated in three fjord areas in the Varanger region with low, moderate and very high crab abundances, respectively. Compared with data from 1994, most benthic species were markedly reduced in abundance, in particular non-moving burrowing and tube-dwelling polychaetes, bivalves and echinoderms. However, a few species appeared to recover from 2007–09 to 2012. Changes in ecological functioning were assessed using ‘biological traits analysis (BTA)’. Following the crab invasion there was a relative reduction of suspension and surface deposit feeding species, an increase in mobile and predatory organisms and an increase in those with planktotrophic larval development. From low to high crab abundances functioning changed from tube-building, deep deposit feeding and fairly large size to free-living, shallow burrowing and rather small size. With regard to sediment reworking, downward and upward conveyors were reduced whereas surficial modifiers increased. The changes imply that sediment biomixing and bioirrigation were reduced leading to a degraded sedimentary environment. It is suggested that establishing relationships between ecosystem functioning and crab abundances may form the basis for estimating ecological costs of the crab invasion. Such knowledge is important for managing the crab in the Barents Sea area being both a non-indigenous species affecting native ecosystems as well as a valuable resource for commercial fishery.

De novo transcriptome assembly and developmental mode specific gene expression of Pygospio elegans.

Species with multiple different larval developmental modes are interesting models for the study of mechanisms underlying developmental mode transitions and life history evolution. Pygospio elegans, a small, tube-dwelling polychaete worm commonly found in estuarine and marine habitats around the northern hemisphere, is one species with variable developmental modes. To provide new genomic resources for studying P. elegans and to address the differences in gene expression between individuals producing offspring with different larval developmental modes, we performed whole transcriptome Illumina RNA sequencing of adult worms from two populations and prepared a de novo assembly of the P. elegans transcriptome. The transcriptome comprises 66,233 unigenes, of which 33,807 contain predicted coding sequences, 26,448 have at least one functional annotation, and 3,076 are classified as putative long non-coding RNAs. We found more than 8,000 unigenes significantly differentially expressed between adult worms from populations producing either planktonic or benthic larvae. This comprehensive transcriptome resource for P. elegans adds to the available genomic data for annelids and can be used to uncover mechanisms allowing developmental variation in this and potentially other marine invertebrate species.

Upper Pleistocene cold-water corals from the Inner Sea of the Maldives: taphonomy and environment

Cold-water corals of the Late Pleistocene (21,400–22,500 BP) are recorded from the sea-bottom of two inter-atoll channels (Kardiva Channel at 457-m depth and Male Vaadhoo Channel at 443-m depth) of the eastern row of the Maldives archipelago. Coral assemblages are composed mainly by Lophelia pertusa and secondarily by Madrepora oculata and Enallopsammia rostrata. These cold-water coral patches are places where the benthic life, mainly sessile, is concentrated, which is clearly absent off-rubble patches. The main epibionts are tube-dwelling polychaetes (mainly Spirorbis and Serpula), bryozoans, siliceous sponges, barnacles, gorgonids, solitary corals, encrusting foraminifera, and microbial mats. The analysis of epibionts assemblages shows different biocoenoses between both studied sites as well as a dependency of the epibiont coverage with regard to the coral genus. Some living benthic organisms such as brachiopods, bivalves, gastropods, barnacles, and ophiuroids find refuge among coral branches. The common record of juvenile specimens of vagile organisms such as small ophiuroids, is probably related to the nursery function of the cold-water corals in spite they are fossils. Environmental requirements of Recent cold-water corals (Lophelia, Madrepora and Enallopsammia) differ of conditions at both sampling sites with sensibly lower oxygenation degree and density of waters than needed for cold-water corals. Therefore, it is proposed that the present-day oxygen and density conditions are the factors which inhibit modern cold-water coral growth in the inter-atoll channels.

Textures and traction: how tube‐dwelling polychaetes get a leg up

By controlling the traction between its body and the tube wall, a tube-dwelling polychaete can move efficiently from one end of its tube to the other, brace its body during normal functions (e.g., ventilation and feeding), and anchor within its tube avoiding removal by predators. To examine the potential physical interaction between worms and the tubes they live in, scanning electron microscopy was used to reveal and quantify the morphology of worm bodies and the tubes they produce for species representing 13 families of tube-dwelling polychaetes. In the tubes of most species there were macroscopic or nearly macroscopic (∼10 μm–1 mm) bumps or ridges that protruded slightly into the lumen of the tube; these could provide purchase as a worm moves or anchors. At this scale (∼10 μm-1 mm), the surfaces of the chaetal heads that interact with the tube wall were typically small enough to fit within spaces between these bumps (created by the inward projection of exogenous materials incorporated into the tube wall) or ridges (made by secretions on the interior surface of the tube). At a finer scale (0.01–10 μm), there was a second overlap in size, usually between the dentition on the surfaces of chaetae that interact with the tube walls and the texture provided by the secreted strands or microscopic inclusions of the inner linings. These linings had a surprising diversity of micro-textures. The most common micro-texture was a “fabric” of secreted threads, but there were also orderly micro-ridges, wrinkles, and rugose surfaces provided by microorganisms incorporated into the inner tube lining. Understanding the fine structures of tubes in conjunction with the morphologies of the worms that build them gives insight into how tubes are constructed and how worms live within them.