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Caudofoveata is a class of worm-like molluscs (aplacophorans) that typically have an infaunal lifestyle, burrowing in soft bottoms in a wide range of marine habitats from shallow to deep waters. Here, we describe a very large new species of caudofoveate from South China Sea methane seeps growing up to 154 mm in length: Chaetoderma shenloong sp. nov. It is the first caudofoveate to be named from a chemosynthetic ecosystem and the first aplacophoran mollusc associated with seeps. Our new species stands out from other Pacific Chaetoderma species by its large size, a wide body relative to its length, a barely sclerotised radula, and the presence of isosceles-triangular sclerites. Phylogenetic reconstruction using the mitochondrial cytochrome c oxidase subunit I (COI) gene placed it within a paraphyletic clade comprising Chaetodermatidae and Limifossoridae, in line with a previous phylogenetic analysis. This also revealed that C. shenloong sp. nov. is conspecific with a Chaetoderma sp. whose whole genome was recently sequenced and assembled but remained undescribed until now. The most closely related species with an available COI sequence was C. felderi, the largest caudofoveate species recorded. Our discovery suggests caudofoveates may be present in other seeps globally but so far neglected; a potential example is C. felderi from the Gulf of Mexico, where seeps are abundant but whose exact habitat remains unclear. [ABSTRACT FROM AUTHOR]

* Many molluscan genomes have been published to date, however only three are from representatives of the subphylum Aculifera (Polyplacophora, Caudofoveata, and Solenogastres), the sister taxon to all other molluscs. Currently, genomic resources are completely lacking for Solenogastres. This gap in knowledge hinders comparative and evolutionary studies. Here, we sequenced the genomes of the solenogaster aplacophorans Epimenia babai Salvini-Plawen, 1997 and Neomenia megatrapezata Salvini-Plawen & Paar-Gausch, 2004 using a hybrid approach combining Oxford Nanopore and Illumina reads. For E. babai, we produced a 628 Mbp haploid assembly (N50 = 413 Kbp, L50 = 370) that is rather complete with a BUSCO completeness score of 90.1% (82.0% single, 8.1% duplicated, 6.0% fragmented, and 3.9% missing). For N. megatrapezata, we produced a 412 Mbp haploid assembly (N50 = 132 Kbp, L50 = 881) that is also rather complete with a BUSCO completeness score of 85.1% (81.7% single, 3.4% duplicated, 8.1% fragmented, and 6.8% missing). Our annotation pipeline predicted 25,393 gene models for E. babai with a BUSCO score of 92.4% (80.5% single, 11.9% duplicated, 4.9% fragmented, and 2.7% missing) and 22,463 gene models for N. megatrapezata with a BUSCO score of 90.2% (81.0% single, 9.2% duplicated, 4.7% fragmented, and 5.1% missing). Phylogenomic analysis recovered Solenogastres as the sister taxon to Polyplacophora and Aculifera as the sister taxon to all other sampled molluscs with maximal support. These represent the first whole-genome resources for Solenogastres and will be valuable for future studies investigating this understudied group and molluscan evolution as a whole.

Caudofoveata is a clade of worm‐like mollusks that lead a burrowing lifestyle in soft marine sediments. There are only a few references to peristaltic movement in members of Caudofoveata. The movement of individuals of Chaetoderma nitidulum collected from the White Sea and set into a transparent gelatin substrate was described by direct observation. The morphology and ultrastructure of the musculature and circulatory system were described in detail using morphological methods (light and electron microscopy, and 3D reconstruction from a series of semithin sections). Based on the analysis of the movement and morphology of the body wall and body cavities, the main phases of movement were distinguished. The peristaltic movement observed in C. nitidulum is superficially similar to the peristalsis phases described for Annelida and completely coincides with the classical description of direct peristalsis. [ABSTRACT FROM AUTHOR]

[Display omitted] • Body size highly dynamic over solenogaster evolution between meio-, macro- and megafaunal size. • Maximum likelihood and Bayesian inference analyses conflict at base of Solenogastres tree. • Most Solenogastres evolved from a macrofaunal ancestor with scale-like sclerites and a distichous radula. • Heterochrony is a potential pathway leading to paedomorphosis within Solenogastres. Body size is a fundamental characteristic of animals that impacts every aspect of their biology from anatomical complexity to ecology. In Mollusca, Solenogastres has been considered important to understanding the group's early evolution as most morphology-based phylogenetic reconstructions placed it as an early branching molluscan lineage. Under this scenario, molluscs were thought to have evolved from a small, turbellarian-like ancestor and small (i.e., macrofaunal) body size was inferred to be plesiomorphic for Solenogastres. More recently, phylogenomic studies have shown that aplacophorans (Solenogastres + Caudofoveata) form a clade with chitons (Polyplacophora), which is sister to all other molluscs, suggesting a relatively large-bodied (i.e., megafaunal) ancestor for Mollusca. Meanwhile, recent investigations into aplacophoran phylogeny have called the assumption that the last common ancestor of Solenogastres was small-bodied into question, but sampling of meiofaunal species was limited, biasing these studies towards large-bodied taxa and leaving fundamental questions about solenogaster body size evolution unanswered. Here, we supplemented available data with transcriptomes from eight diverse meiofaunal species of Solenogastres and conducted phylogenomic analyses on datasets of up to 949 genes. Maximum likelihood analyses support the meiofaunal family Meiomeniidae as the sister group to all other solenogasters, congruent with earlier ideas of a small-bodied ancestor of Solenogastres. In contrast, Bayesian Inference analyses support the large-bodied family Amphimeniidae as the sister group to all other solenogasters. Investigation of phylogenetic signal by comparing site-wise likelihood scores for the two competing hypotheses support the Meiomeniidae-first topology. In light of these results, we performed ancestral character state reconstruction to explore the implications of both hypotheses on understanding of Solenogaster evolution and review previous hypotheses about body size evolution and its potential consequences for solenogaster biology. Both hypotheses imply that body size evolution has been highly dynamic over the course of solenogaster evolution and that their relatively static body plan has successfully allowed for evolutionary transitions between meio-, macro- and megafaunal size ranges. [ABSTRACT FROM AUTHOR]

Aplacophora is a small enigmatic group of worm-like molluscs covered by sclerites. The general morphology of the posterior end, including the gonopericardial system, in many species is well studied using light microscopy. However, knowledge of the ultrastructure of this complex is fragmentary and many questions concerning the excretion of metabolites in this group still remain. The gonopericardial system of Chaetoderma nitidulum Lovén, 1844 (Caudofoveata) from the White Sea was studied using light microscopy and 3D reconstruction from a series of semi-thin sections. The ultrastructure of the gonopericardial system was described in detail for the first time. The gonopericardial complex consists of gonads connected to the pericardium by ciliated paired gonopericardioducts. The pair of gonoducts begins at the lateral sides of the pericardium and opens into the mantle cavity. Gonoducts consist of upper and lower parts that are morphologically differentiated. The walls of the upper gonoducts consist of cells that likely participate in the excretion of metabolites and reabsorption of useful substances. Lower gonoducts are bulk bags with a small cell wall, in which there is a ciliary tract, likely for the excretion of metabolites and reproductive products. Spermatozoa were found at different stages of development in different parts of the pericardium and gonoducts. On the basis of previously published and newly obtained data, the process of excretion by C. nitidulum is proposed. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The shell-less, worm-shaped Caudofoveata is one of the least known groups of molluscs. • 38 species from all recognized families of Caudofoveata were included in the analyses. • Contrary to traditional views, Prochaetodermatidae is sister to the other families. • Current classification of Caudofoveata is in need of revision. • Evolutionary scenarios for Caudofoveata differ from previously proposed hypotheses. Abstract The shell-less, worm-shaped Caudofoveata (=Chaetodermomorpha) is one of the least known groups of molluscs. The taxon consists of 141 recognized species found from intertidal environments to the deep-sea where they live burrowing in sediment. Evolutionary relationships of the group have been debated, but few studies based on morphological or molecular data have investigated the phylogeny of the group. Here we use molecular phylogenetics to resolve relationships among and within families of Caudofoveata. Phylogenetic analyses were performed using selected mitochondrial and nuclear genes from species from all recognized families of Caudofoveata. In resulting trees and contrary to traditional views, Prochaetodermatidae forms the sister clade to a clade containing the other two currently recognized families, Chaetodermatidae and Limifossoridae. The monophyly of Prochaetodermatidae is highly supported, but Limifossoridae and Chaetodermatidae are not recovered as monophyletic. Most of the caudofoveate genera are also not recovered as monophyletic in our analyses. Thus results from our molecular data suggest that the current classification of Caudofoveata is in need of revision, and indicate evolutionary scenarios that differ from previously proposed hypotheses based on morphology. [ABSTRACT FROM AUTHOR]

Aplacophorans are well known as exclusively marine benthic molluscs with a vermiform body covered by aragonitic sclerites (also called spicules), whose species are widely distributed from the sublittoral down to the abyss. Currently, only nine species are known from Brazil (one Solenogastres and eight Caudofoveata), but these very few records are no longer a reflection of an existing low diversity. Sampling in deep waters has been conducted recently in oil-rich areas of the Brazilian coast, and the museum collections have now many aplacophoran lots. There is a need to learn about and/or install some microscopical facilities in Brazilian institutions, to form expertise for the investigations on these generally small animals. With studies on taxonomy, phylogeny, biogeography and ecology, important questions will be surely answered about the diversity, distribution, and the relationship among the deep-sea fauna from Brazil and from other places. [ABSTRACT FROM AUTHOR]

Abstract Solenogastres form a small clade of worm-shaped molluscs distributed world-wide with most of the approx. 300 species occurring in the deep sea. A recent diversity study from the abyssal plain in the Northwest Pacific has revealed a wealth of new abyssal solenogaster lineages highlighting the need for further alpha-taxonomic work. During the 'Sea of Okhotsk Biodiversity Studies' (SokhoBio) expedition, 93 specimens were collected at overall eight stations ranging from depths of 1696–3377 m. Preliminary investigations revealed twelve clearly distinguishable morphospecies, including one relatively common species present at six of eleven stations. All morphospecies are characterized externally via light microscopy and identified to the best possible taxonomic level via scleritome characters. Molecular barcodes (16S rRNA) are provided as a first step towards establishment of a barcoding library to enable fast and accurate re-identification of these taxonomically challenging molluscs in future studies. The most wide-spread and abundant cavibelonian Solenogastres Kruppomenia genslerae sp. nov. (Simrothiellidae) is exemplarily described in full microanatomical detail based on 3D-reconstructions from histological semithin section series and scanning electron microscopy. We discuss our results in comparison to the solenogaster diversity of the neighbouring abyssal plain of the Northwest Pacific, which is connected with the Kuril Basin via two straits. Our initial characterization of the diversity boosts the hitherto poorly known diversity of Solenogastres in the Far Eastern Seas, but also underlines the taxonomic impediment for proper taxonomic descriptions of the wealth of new discovered material. [ABSTRACT FROM AUTHOR]

Prochaetodermatidae (Mollusca, Aplacophora, Caudofoveata), typical inhabitants of the deep sea, occur mainly along the continental slope, sometimes in high abundance. Their diversity in some regions, such as the South Atlantic Ocean, is little studied. The genus Claviderma is so far composed of one Pacific Ocean, two Indian Ocean and seven Atlantic Ocean species. Collections of the southeastern Brazilian coast contained three species of this genus. One, C. virium sp. nov., is new to science, and the other two, C. crassum and C. amplum , are new occurrences, extending their distributions southward into the western Atlantic. The external morphology and details of their radula and sclerites are described. The new species is distinguished by its long trunk and comparatively narrow, short posterium, and its trunk sclerites bearing numerous evident transverse growth lines. In the Atlantic Ocean, species with similar body forms and with sclerites of the same shape occur off the western and eastern coasts: the South American C. compactum is similar externally to the African C. brevicaudatum , and the Brazilian C. virium sp. nov. is comparable to the eastern Atlantic C. gladiatum . This suggests that these pairs of species are sister-groups, sharing the same morphological traits as a result of common ancestry. In the western and eastern Atlantic, most species of Claviderma that live over a wider range of depths are more widely distributed. [ABSTRACT FROM AUTHOR]

We present the first DNA taxonomy publication on abyssal Mollusca from the Clarion-Clipperton Zone (CCZ), central Pacific ocean, using material collected as part of the Abyssal Baseline (ABYSSLINE) environmental survey cruise 'AB01' to the UK Seabed Resources Ltd (UKSRL) polymetallic-nodule exploration area 'UK-1' in the eastern CCZ. This is the third paper in a series to provide regional taxonomic data for a region that is undergoing intense deep-sea mineral exploration for high-grade polymetallic nodules. Taxonomic data are presented for 21 species from 42 records identified by a combination of morphological and genetic data, including molecular phylogenetic analyses. These included 3 heterodont bivalves, 5 protobranch bivalves, 4 pteriomorph bivalves, 1 caudofoveate, 1 monoplacophoran, 1 polyplacophoran, 4 scaphopods and 2 solenogastres. Gastropoda were recovered but will be the subject of a future study. Seven taxa matched published morphological descriptions for species with deep Pacific type localities, and our sequences provide the first genetic data for these taxa. One taxon morphologically matched a known cosmopolitan species but with a type locality in a different ocean basin and was assigned the open nomenclature 'cf' as a precautionary approach in taxon assignments to avoid over-estimating species ranges. One taxon is here described as a new species, Ledella knudseni sp. n. For the remaining 12 taxa, we have determined them to be potentially new species, for which we make the raw data, imagery and vouchers available for future taxonomic study. The Clarion-Clipperton Zone is a region undergoing intense exploration for potential deep-sea mineral extraction. We present these data to facilitate future taxonomic and environmental impact study by making both data and voucher materials available through curated and accessible biological collections. [ABSTRACT FROM AUTHOR]

Solenogastres (Mollusca) have a quite uniform bodyplan and an evolutionary history with few shifts out of their deep-water habitat and beyond their epibenthic lifestyle. Consequently, few clades inhabit the shallow subtidal mesopsammon; only Meiomeniidae (order Pholidoskepia) is entirely restricted to this habitat. What was initially designed as a comparative microanatomical redescription of Meiomeniidae to explore the diversity of this clade with its unique evolution, developed into a taxonomic nightmare of cryptic, co-occurring lineages: three out of four valid species of Meiomeniidae co-occur in coarse sands in the Bermuda archipelago and were re-collected at the respective type localities. We analyzed the material combining three-dimensional (3D) reconstructions from histological serial sections and ultrastructural data, providing novel insights into meiomeniid anatomy and discussing potential phylogenetic implications. However, not all collected material could be unambiguously assigned to known lineages of mesopsammic Solenogastres. In addition to meiomeniids, we discovered another co-occurring, externally highly cryptic but anatomically distinguishable lineage. It is provisionally placed within Dondersiidae, but its taxonomic assignment remains problematic due to an exclusive character mosaic and a unique foregut gland complex. Our study reveals the risk of creating chimeric taxa in small-bodied Solenogastres, as morphological characters needed for species delineation cannot be extracted from single individuals, while conspecifity based on external features is risky to assume with cryptic species co-occurring. Molecular markers will be needed to reliably retrieve Meiomeniidae from their current Bermuda Triangle of taxonomy and to proceed in solenogaster taxonomy confronted with a wealth of poorly known lineages especially in meiofaunal forms. [ABSTRACT FROM AUTHOR]

The association of trace fossils from the Late Silurian Río Seco de los Castaños Formation in central-western Argentina (San Rafael Block) is mainly composed of Dictyodora , including Dictyodora scotica , Dictyodora tenuis and a new ichnospecies named Dictyodora atuelica . The latter shows a tendency to migrate to a deeper level – analogous to Dictyodora liebeana 's – which reflects more sophisticated behavioural patterns. The Dictyodora ichnospecies (one of the most diverse assemblages in Gondwana) coexists with Nereites . SEM observations and EDS analyses suggest that the wall structure of Dictyodora could be the result of an activity other than the traditional suggestion of respiration, e.g., feeding. The succession, including some of the levels containing Dictyodora , presents microbially induced sedimentary structures (MISS) that would indicate a photic zone. This discovery favours previous deltaic interpretations instead of the deep-sea fan deposits traditionally suggested for the Siluro-Devonian greywackes of the Cuyania terrane, and particularly for this unit. The abundant Dictyodora , Nereites , Zoophycos and undermat miners ichnofossils, as well as the scarce arthropod trackways, resemble older records in Europe and North America. The studied section is very well age-constrained, and the autochthonous Gondwana ichnofauna permits to cast doubt on previous interpretations, suggesting that after the Ordovician, microbial mats retreated to marginal marine environments and then spread later in the Carboniferous. More importantly, the occurrence of Dictyodora and Nereites in beds that bear abundant wrinkle structures or records of biofilms in some places is challenging with regard to deep-sea interpretations. Dictyodora is probably not a good stratigraphic indicator, and the provincialism suggested for this ichnogenus may be an artefact of the lack of more complete records in Gondwana. [ABSTRACT FROM AUTHOR]

Extant aplacophorans, a group of shell-less vermiform molluscs, respire through appendages within or projecting from a posterior cavity. Respiratory structures differ between the subclasses Caudofoveata (ctenidia within the cavity) and Solenogastres (folds of the mantle itself). Acaenoplax hayae, a Silurian vermiform mollusc from the Herefordshire Lagerstätte, England, exhibits characteristics of both these groups. While recent work places it within the crown group Aplacophora, near the caudofoveates, initial observations suggested that its respiratory structures were closer to those of the solenogastres. Here, we present new reconstructions of the posterior of Acaenoplax prepared with the aim of resolving features obscured when prior studies were undertaken. These reconstructions detail a novel posterior architecture, not closely comparable to that of either extant aplacophoran group, in which respiratory projections arise from a membrane that partly encloses a central posterior cavity. The posterior membrane is flanked by small spherical projections; both membrane and spherical projections are apparently unique within the Aplacophora. The existence of this previously undocumented respiratory system underlines the diversity of the aplacophoran clade during the Palaeozoic. [ABSTRACT FROM AUTHOR]

Background The Solenogastres (or Neomeniomorpha) are a taxon of aplacophoran molluscs with contentious phylogenetic placement. Since available developmental data on non-conchiferan (that is, aculiferan) molluscs mainly stem from polyplacophorans, data on aplacophorans are needed to clarify evolutionary questions concerning the morphological features of the last common ancestor (LCA) of the Aculifera and the entire Mollusca. We therefore investigated the development of the nervous system in two solenogasters, Wirenia argentea and Gymnomenia pellucida, using immunocytochemistry and electron microscopy. Results Nervous system formation starts simultaneously from the apical and abapical pole of the larva with the development of a few cells of the apical organ and a posterior neurogenic domain. A pair of neurite bundles grows out from both the neuropil of the apical organ and the posterior neurogenic domain. After their fusion in the region of the prototroch, which is innervated by an underlying serotonin-like immunoreactive (-LIR) plexus, the larva exhibits two longitudinal neurite bundles - the future lateral nerve cords. The apical organ in its fully developed state exhibits approximately 8 to 10 flask-shaped cells but no peripheral cells. The entire ventral nervous system, which includes a pair of longitudinal neurite bundles (the future ventral nerve cords) and a serotonin-LIR ventromedian nerve plexus, appears simultaneously and is established after the lateral nervous system. During metamorphosis the apical organ and the prototrochal nerve plexus are lost. Conclusions The development of the nervous system in early solenogaster larvae shows striking similarities to other spiralians, especially polychaetes, in exhibiting an apical organ with flask-shaped cells, a single pair of longitudinal neurite bundles, a serotonin-LIR innervation of the prototroch, and formation of these structures from an anterior and a posterior neurogenic domain. This provides evidence for an ancestral spiralian pattern of early nervous system development and a LCA of the Spiralia with a single pair of nerve cords. In later nervous system development, however, the annelids deviate from all other spiralians including solenogasters in forming a posterior growth zone, which initiates teloblastic growth. Since this mode of organogenesis is confined to annelids, we conclude that the LCA of both molluscs and spiralians was unsegmented. [ABSTRACT FROM AUTHOR]

Recent advances in fossil, developmental and molecular studies show that aplacophorans are derived molluscs that evolved from chiton-like ancestors presumably in the Ordovician period (488–440 Ma), thereby forming the clade Aculifera along with extant polyplacophorans. Other major molluscan groups (i.e. bivalves and gastropods) diversified in the Early Cambrian along with a suite of distinct sclerite-bearing forms, such asHalkieriaPoulsen, 1967 and other sachitids. These extend the aculiferan stem lineage into the Cambrian. Both fossil data and molecular divergence estimates find that modern chitons (the crown group) originated in the Carboniferous period (about 340 Ma) and that the major group of chitons with slitted insertion plates (Chitonida) originated in the Permian (about 260–270 Ma). A distinct and peculiar lineage of stem group chitons is the 17-plated multiplacophorans, which diversified prior to the Silurian, Wenlock (about 426 Ma) and evolved a number of characteristics similar to certain crown group chitons convergently. Multiplacophorans likely inhabited more exposed substrates, which demanded a tougher and integrated armour as observed in some modern chitons. [ABSTRACT FROM AUTHOR]

The class Solenogastres (sensuSalvini-Plawen, 1967) includes approximately 270 described species, 30% of which can be found off the Atlantic and Mediterranean coasts of Europe. From the Iberian Peninsula, 36 species are known, and six are cited from the Southern Peninsula from Gorringe Bank to Cabo de Gata. The results of a study of a collection of 81 specimens are presented here. Solenogastres were collected from seafloors off the South Iberian Peninsula during three expeditions: DEEPER [Desarrollo de Estudios de Ecosistemas de Profundidad bajo un Enfoque interdisciplinar] 0409, INDEMARES [Inventario y designación en la Red Natura 2000 en áreas marinas del Estado Español]/Chica 0610–0211 and INDEMARES/Alborán 0911. Analysis of the collected solenogaster specimens resulted in the discovery of a new species, which is described here asAlexandromenia avempacensissp. nov, along with the identification of four already known species:Unciherpia hirsutaGarcia-Alvarez, Salvini-Plawen and Urgorri, 2001, which had not been reported from the South of the Peninsula before andNeomenia carinataTullberg, 1875,Anamenia gorgonophila(Kowalevsky, 1880) andDorymenia sarsii(Koren & Danielssen, 1877), whose presence in this area was already known. New anatomical and ecological data regarding these species are also provided. The anatomical reconstruction of the anterior and posterior body ends ofNeomenia carinatais presented in addition to a more detailed and extensive description of its copulatory spicules. A broader and more complete description of the sclerites of this species is also provided. The study of thehabitus, hard parts and histological sections ofDorymenia sarsiipoints towards a synonymy betweenD. sarsiiandD. tortilisScheltema & Schander, 2000. Ecological data related to the accompanying fauna and the type of substratum for each species described is also provided. http://zoobank.org/urn:lsid:zoobank.org:pub:EA987A53-FF5D-463F-A072-0EA99BCDA129 [ABSTRACT FROM AUTHOR]

The morphology and internal anatomy of the caudofoveateFalcidens vasconiensisSalvini-Plawen, 1996, are described and a 3D reconstruction of its anatomy is made with the program AVIZO 6.3.1. The detailed body shape, additional sclerite types, digestive system, and nervous system ofF. vasconiensisare described for the first time. The nine specimens studied here were collected off the NW Iberian Peninsula between 150 and 600 m depth during the expeditions DIVA-ArtabriaI 2002 and 2003, Vertidos2004, and ASelva2008. [ABSTRACT FROM AUTHOR]

Background: With more than 100000 living species, mollusks are the second most diverse metazoan phylum. The current taxonomic classification of mollusks recognizes eight classes (Neomeniomorpha, Chaetodermomorpha, Polyplacophora, Monoplacophora, Cephalopoda, Gastropoda, Bivalvia, and Scaphopoda) that exhibit very distinct body plans. In the past, phylogenetic relationships among mollusk classes have been contentious due to the lack of indisputable morphological synapomorphies. Fortunately, recent phylogenetic analyses based on multi-gene data sets are rendering promising results. In this regard, mitochondrial genomes have been widely used to reconstruct deep phylogenies. For mollusks, complete mitochondrial genomes are mostly available for gastropods, bivalves, and cephalopods, whereas other less-diverse lineages have few or none reported. Results: The complete DNA sequence (14662 bp) of the mitochondrial genome of the chaetodermomorph Scutopus ventrolineatus Salvini-Plawen, 1968 was determined. Compared with other mollusks, the relative position of protein-coding genes in the mitochondrial genome of S. ventrolineatus is very similar to those reported for Polyplacophora, Cephalopoda and early-diverging lineages of Bivalvia and Gastropoda (Vetigastropoda and Neritimorpha; but not Patellogastropoda). The reconstructed phylogenetic tree based on combined mitochondrial and nuclear sequence data recovered monophyletic Aplacophora, Aculifera, and Conchifera. Within the latter, Cephalopoda was the sister group of Gastropoda and Bivalvia + Scaphopoda. Conclusions: Phylogenetic analyses of mitochondrial sequences showed strong among-lineage rate heterogeneity that produced long-branch attraction biases. Removal of long branches (namely those of bivalves and patellogastropods) ameliorated but not fully resolved the problem. Best results in terms of statistical support were achieved when mitochondrial and nuclear sequence data were concatenated. [ABSTRACT FROM AUTHOR]

During August-September 2011, scientists aboard the R/V Meteor sampled marine animals around Iceland for the IceAGE project (Icelandic marine Animals: Genetics and Ecology). The last sample was taken at a site known as "The Rose Garden" off northeastern Iceland and yielded a large number of two species of Proneomenia (Mollusca, Aplacophora, Solenogastres, Cavibelonia, Proneomeniidae). We examined isolated sclerites, radulae, and histological section series for both species. The first, Proneomenia sluiteri Hubrecht, 1880, was originally described from the Barents Sea. This is the first record of this species in Icelandic waters. However, examination of aplacophoran lots collected during the earlier BIOICE campaign revealed additional Icelandic localities from which this species was collected previously. The second represents a new species of Proneomenia, which, unlike other known representatives of the genus, broods juveniles in the mantle cavity. We provide a formal description, proposing the name Proneomenia custodiens sp. n. Interestingly, the sclerites of brooded juveniles are scales like those found in the putatively plesiomorphic order Pholidoskepia rather than hollow needles like those of the adults of this species. Cytochrome c oxidase subunit I (COI) DNA barcode sequences are provided for both species of Proneomenia. [ABSTRACT FROM AUTHOR]

The first records from samples from the IceAGE cruise ME85/3 in 2011 include seven species of Caudofoveata with a distribution range in Icelandic waters. From this first cruise of the project, two new records for Iceland have been registered. Psilodens balduri sp. n. is new to science and Falcidens halanychi, with a known distribution in the American North-Atlantic, is new to Iceland. The current study thus increases the number of known caudofoveate species around Iceland to nine. [ABSTRACT FROM AUTHOR]

Information regarding the molluscs in this dataset is based on the Rauschert dredge samples collected during the Latitudinal Gradient Program (LGP) on board the R/V "Italica" in the Ross Sea (Antarctica) in the austral summer 2004. A total of 18 epibenthic dredge deployments/samplings have been performed at four different locations at depths ranging from 84 to 515m by using a Rauschert dredge with a mesh size of 500μm. In total 8,359 specimens have been collected belonging to a total of 161 species. Considering this dataset in terms of occurrences, it corresponds to 505 discrete distributional records (incidence data). Of these, in order of abundance, 5,965 specimens were Gastropoda (accounting for 113 species), 1,323 were Bivalvia (accounting for 36 species), 949 were Aplacophora (accounting for 7 species), 74 specimens were Scaphopoda (3 species), 38 were Monoplacophora (1 species) and, finally, 10 specimens were Polyplacophora (1 species). This data set represents the first large-scale survey of benthic micro-molluscs for the area and provides important information about the distribution of several species, which have been seldom or never recorded before in the Ross Sea. All vouchers are permanently stored at the Italian National Antarctic Museum (MNA), Section of Genoa, enabling future comparison and crosschecking. This material is also currently under study, from a molecular point of view, by the barcoding project "BAMBi" (PNRA 2010/A1.10). [ABSTRACT FROM AUTHOR]

Information regarding the molluscs in this dataset is based on the epibenthic sledge (EBS) samples collected during the cruise BIOPEARL II / JR179 RRS James Clark Ross in the austral summer 2008. A total of 35 epibenthic sledge deployments have been performed at five locations in the Amundsen Sea at Pine Island Bay (PIB) and the Amundsen Sea Embayment (ASE) at depths ranging from 476 to 3501m. This presents a unique and important collection for the Antarctic benthic biodiversity assessment as the Amundsen Sea remains one of the least known regions in Antarctica. Indeed the work presented in this dataset is based on the first benthic samples collected with an EBS in the Amundsen Sea. However we assume that the data represented are an underestimation of the real fauna present in the Amundsen Sea. In total 9261 specimens belonging to 6 classes 55 families and 97 morphospecies were collected. The species richness per station varied between 6 and 43. Gastropoda were most species rich 50 species followed by Bivalvia (37), Aplacophora (5), Scaphopoda (3) and one from each of Polyplacophora and Monoplacophora. [ABSTRACT FROM AUTHOR]

The deep-sea hydrothermal vent solenogaster Helicoradomenia is covered with calcium carbonate sclerites. Light and electron microscopy reveal varying morphologies of these sclerites. Many sclerites have hollow tips and/or are pitted and etched. Bacteria are found on and in sclerites. Initial sclerite formation occurs in an extracellular crystalline chamber formed by the invagination of a cuboidal basal cell of the columnar microvillus mantle epithelium. As the sclerite grows, it fills the crystalline chamber resulting in direct contact with the microvilli of both the basal cell and neighboring secondary sclerite-forming cells. These cells shape a collar around the base of the growing sclerite. As growth continues, the sclerite-forming cells stretch around the sclerite forming a sheath in which the base of the sclerite resides. Mature sclerites grow through the cuticle into the external environment. The erosion pattern of sclerites reveals a less stable inner medullary region and a harder outer cortical region. This points to a secondary character state, where foremost hollow acicular sclerites develop into solid sclerites. This is in agreement with the systematic position of the genus Helicoradomenia within Simrothiellidae, a taxon typically with hollow sclerites. [ABSTRACT FROM AUTHOR]

The nervous system of invertebrates is considered to be a very conservative organ system and thus can be helpful to elucidate questions of phylogenetic relationships. Up to now, comparative neuroanatomical studies have been mainly focused on arthropods, where in-depth studies on major brain structures are abundant. In contrast, except for Gastropoda and Cephalopoda, the nervous system of representatives of the second largest phylum of invertebrates, the Mollusca, is as yet hardly investigated. We therefore initiated an immunohistochemical survey to contribute new neuroanatomical data for several molluscan taxa, especially the lesser known Caudofoveata, Solenogastres, Polyplacophora, and Scaphopoda, focusing on the cellular architecture and distribution of neurotransmitters in the brain. Antisera against the widespread neuroactive substances FMRFamide and serotonin were used to label subsets of neurons. Both antisera were additionally used in combination with acetylated α-tubulin and the nuclear marker DAPI. This enables us to describe the morphology of the nervous system at a fine resolution and to compare its cellular architecture between different species of one taxon, as well as between different taxa of mollusks. On the basis of these results, the nervous system of caudofoveates seems to be most highly derived within the so-called basal (non-conchiferan) mollusks, and a monophyly of a clade Aplacophora could not be confirmed. In general, the brain as well as the remaining nervous system of the molluscan taxa investigated shows a great variability, suggesting a deep time origin of the diversification of this prominent protostome clade. [ABSTRACT FROM AUTHOR]

Abstract: A consensus on molluscan relationships has yet to be achieved, largely because of conflicting morphological and molecular hypotheses. Monoplacophora show marked seriality of ctenidia, atria, muscles and nephridia and this has been interpreted as plesiomorphic for Mollusca, reflecting a segmented ancestry. More recently this seriality, also partly seen in Polyplacophora, has been seen as a derived condition. Analysis of the first published monoplacophoran DNA sequence from Laevilipilina antarctica Warén & Hain, 1992 [Giribet, G., Okusu, A., Lindgren, A.R., Huff, S., Schrödl, M., Nishiguchi, M.K., 2006. Evidence for a clade composed of molluscs with serially repeated structures: Monoplacophorans are related to chitons. Proc. Natl. Acad. Sci. USA 103, 7723–7728. 10.1073/pnas.0602578103], showed Monoplacophora inside Polyplacophora. These taxa were then grouped under the name Serialia, reflecting the hypothesis that their seriality is a synapomorphy. Subsequent examination revealed that part of the L. antarctica published sequence was the result of contamination with Polyplacophora (Giribet, Supplementary Material S1). We collected and sequenced another monoplacophoran, Laevipilina hyalina McLean, 1979, resulting in the first multi-gene dataset representing all molluscan classes. Our analyses did not show unambiguous support for Serialia. Model-based approaches strongly supported Serialia as a clade, however, parsimony analyses under dynamic and static homology did not resolve the position of Monoplacophora. Although our study provides support for Serialia and none for Conchifera, it appears that further resolution of molluscan relationships will require large increases of data. [Copyright &y& Elsevier]

The morphology of the nervous system of Wirenia argentea (Solenogastres) is described based on histological and immunocytochemical analyses using fluorescent markers against the neurotransmitters serotonin and FMRFamide, as well as acetylated α-tubulin, in combination with confocal laser-scanning microscopy. The nervous system displays a distinct tetraneury with fused cerebral ganglia, large pedal ganglia, and longitudinal nerve cords connected by regularly spaced connectives and commissures resulting in an orthogon-like arrangement. There is no indication of metamery. FMRFamidergic immunoreactivity is present in most compartments of the nervous system, while serotonergic immunoreactivity appears to be restricted to the longitudinal nerve cords, the cerebro-pedal commissure and part of the cerebral ganglion. The buccal system shows immunoreactivity against none of the neurotransmitters. [ABSTRACT FROM AUTHOR]

During a cruise with R/V Oceanus out of Woods Hole organized by the National Science Foundation project WormNet, a new species of chaetodermomorph aplacophoran was found in the northwestern Atlantic on the continental rise, between 1100 and nearly 2900 m. An investigation into the material of older collections revealed that the species had previously been collected on numerous occasions but remained undescribed. We here describe the species under the name Falcidens halanychi sp. nov. The species is compared with F. limifossorides Salvini-Plawen 1992 that has the most similar overall morphology, but occurs in the eastern Pacific at lower slope and abyssal depths between 3700 and 4300 m. We illustrate the radula of limifossorides and the birefringent colours of the sclerites photographically for the first time. We also include two DNA barcodes of F.halanychi (cytochome oxidase I) to aid future molecular identification. [ABSTRACT FROM AUTHOR]

Acaenoplax hayae is a spinose worm-like animal from the Silurian Herefordshire Lagerstätte of England, a deposit that preserves high-fidelity soft-part morphology of invertebrates in three dimensions. Specimens have been serially ground and reconstructed by computer to their three-dimensional form. Acaenoplax bears serially repeated transverse ridges dorsally, each with an array of probably aragonitic spines inclined posteriorly. Oblique ventral lobe-rows correspond in position to the dorsal ridges. Aragonitic dorsal valves overlie every third ridge; the penultimate valve is absent leaving a total of seven. The anterior termination is disk-like, surrounding an antero-medial mouth. At the posterior termination there is a cavity between the posteriormost dorsal and a posteroventral valve, from which soft-part projections extend. Acaenoplax is interpreted as a creeping epibenthic animal that fed on sessile prey. It is an ‘aculiferan’ mollusc, combining unique autapomorphic structures with characters typical of the Polyplacophora and Aplacophora. Its morphology can be accommodated within both of the competing schemes of molluscan phylogeny, and its closest living relatives in both cases are aplacophorans. The highly serialized morphology of Acaenoplax is unique within the Mollusca, but the pattern it highlights is an attractive candidate for the primitive state of serial repetition within the phylum. [ABSTRACT FROM AUTHOR]