Deep-sea methane seeps host diverse and abundant animal communities, including an extensive undescribed diversity of small cryptic invertebrates. We describe a new genus and species of neomphalid snail, Levinaespira georgesnyderi gen. et sp. nov., from the Mound 12 methane seep at 1000 m depth on the Pacific margin of Costa Rica, and we report a closely related singleton specimen from the Hydrate Ridge seep off Oregon, USA, at ca. 600 m depth. Molecular phylogenies based on the mitochondrial cytochrome c oxidase subunit I (COI) gene and the complete mitochondrial genome support the placement of the new genus within Neomphalidae (Gastropoda: Neomphalida), a group originally described from hydrothermal vents. Levinaespira georgesnyderi gen. et sp. nov. is separated from species in other described genera by at least 15.2% COI distance. It is morphologically distinctive in having lateral projections on the anterior foot, a lobe-shaped right cephalic lappet, and bilaterally symmetric cephalic tentacles without obvious reproductive modifications. This species represents the first genetically confirmed record of Neomphalidae at methane seeps and the shallowest known occurrence of this group at any environment. The new genus is named in honor of Professor Emerita Lisa Levin and the new species is named in memory of Collection Manager H. George Snyder (1931-1990) for their contributions to deep-sea invertebrate biology.

The methane seeps on the Pacific margin of Costa Rica support extensive animal diversity and offer insights into deep-sea biogeography. During five expeditions between 2009 and 2019, we conducted intensive faunal sampling via 63 submersible dives to 11 localities at depths of 300–3600 m. Based on these expeditions and published literature, we compiled voucher specimens, images, and 274 newly published DNA sequences to present a taxonomic inventory of macrofaunal and megafaunal diversity with a focus on invertebrates. In total 488 morphospecies were identified, representing the highest number of distinct morphospecies published from a single seep or vent region to date. Of these, 131 are described species, at least 58 are undescribed species, and the remainder include some degree of taxonomic uncertainty, likely representing additional undescribed species. Of the described species, 38 are known only from the Costa Rica seeps and their vicinity. Fifteen range extensions are also reported for species known from Mexico, the Galápagos seamounts, Chile, and the western Pacific; as well as 16 new depth records and three new seep records for species known to occur at vents or organic falls. No single evolutionary narrative explains the patterns of biodiversity at these seeps, as even morphologically indistinguishable species can show different biogeographic affinities, biogeographic ranges, or depth ranges. The value of careful molecular taxonomy and comprehensive specimen-based regional inventories is emphasized for biodiversity research and monitoring.

ABSTRACT The phylogenetic position of Haloceratidae, a little-known family of the subclass Caenogastropoda, is contested due to its extreme rarity in bathyal waters worldwide (c. 800–3,500 m deep). Haloceratids share several morphological and ecological traits with members of Vanikoroidea, Tonnoidea, Capuloidea and Velutinoidea, and were provisionally included in Vanikoroidea based on the absence of certain apomorphic features of the latter three taxa. Here, we first investigate the phylogenetic position of the family based on molecular data from both of the recognized genera, Haloceras and Zygoceras. Reconstruction based on three nuclear and three mitochondrial gene sequences suggests that the Haloceratidae constitute a sister clade to the Capulidae and that the two families collectively form the superfamily Capuloidea. This superfamily is united in a large, robust clade with Calyptraeoidea, Velutinoidea, Tonnoidea and Neogastropoda. The superfamily Cypraeoidea, as previously conceived, was found to be polyphyletic; we propose new concepts of Cypraeoidea (including Cypraeidae and Ovulidae) and Velutinoidea (including Velutinidae, Eratoidae and Triviidae). This topology also confirms the polyphyly of taxa with the ‘echinospira’ type of larvae (Echinospirida). The morphological resemblance of these polyphyletic taxa highlights parallel acquisition of traits in response to the same selective pressures.

Benthic invertebrates at deep-sea hydrothermal vents and cold seeps have attracted considerable attention regarding their spatiotemporal distributions, colonization pathways, geological origins and morphological, ecological and physiological adaptations. Here we first reconstruct a molecular phylogeny for vent and seep species in the gastropod subclass Neritimorpha based on combined mitochondrial and nuclear gene sequences. The resulting tree, in conjunction with anatomical and palaeontological evidence, indicates that neritimorph snails and limpets in the Cenozoic deep-sea chemosynthetic habitats belong to the monophyletic subfamily Shinkailepadinae (family Phenacolepadidae). Confamilial shallow-water species form its sister clade, the subfamily Phenacolepadinae. There were probably at least three independent shifts from the coiled snail with a functional operculum to the limpet form in the evolutionary history of the family, twice in the deep-sea Shinkailepadinae and once in the shallow-water Phenacolepadinae. Physiological and ecological characteristics including the presence of red blood cells and larval migration seem to have facilitated their early Cenozoic colonization of vents and seeps. The type specimens of type species were investigated for most nominal genera to amend generic classification of this long-neglected family. A monotypic Divia gen. nov. is proposed for Shinkailepas briandi; Shinkailepas and Thalassonerita pre-date Olgasolaris and Bathynerita, respectively.

An eulimid gastropod, Megadenus atrae n. sp., endoparasitic in the cloacal chamber of the black sea cucumber Holothuria atra Jaeger is described from Okinawa, Japan, as the fifth species of the genus. Conspecific specimens have also been found from southeast India, northeast Australia and New Caledonia. The generic assignment is justified by the presence of (i) a thick, long proboscis that bears a large fold (pseudopallium) near the base and a collar-like structure at the middle, (ii) a thin, globose shell that is covered by the pseudopallium, and (iii) sexual dimorphism with the female generally larger than the male. The new species is distinguishable from the four previously described congeners by its cauldron-shaped pseudopallium, moderately-developed collar of the proboscis and rounded basal lip of the shell. The comparisons of the size and sex of solitary and paired individuals support a previous hypothesis that the species of Megadenus Rosén, 1910 are protandrous with environmental sex determination. The present species occurs mostly as monogamous pairs despite its very low population density, implying that the presence of a conspecific individual acts as a cue for larval settlement. Both mechanisms would increase individual reproductive success in such permanent parasites with low prevalence and abundance as the species of Megadenus.

A new species of Parvaplustrum from the northeastern Pacific, recognized in the literature as undescribed, is formally named herein. This new species is morphologically distinct from the two other species in the genus, Parvaplustrum tenerum and P. japonicurn, and distinguishable by its shell sculpture. The new species is found from Oregon to Baja California, typically associated with chemosynthetic deep-water environments and organic-rich sediments.

The red-blooded limpet ‘Shinkailepas’briandi(Neritimorpha: Phenacolepadidae) is one of the commonest gastropod species at deep-sea hydrothermal vents on the Mid-Atlantic Ridge (MAR). We investigated its population connectivity along MAR as the first such study for gastropods and explored the importance of larval migration for the distribution of vent-endemic animals. Our analyses, based on 1.3-kbp DNA sequences from the mitochondrial COI gene, showed a panmictic population throughout its geographic and bathymetric ranges that span from the northernmost and shallowest Menez Gwen vent field (38°N; 814–831 m depth) to the southernmost and deepest Ashadze field (13°N; 4090 m). Early development of this species is presumed to have a long pelagic duration as a planktotrophic larva; the hatchling with a shell diameter of 170–180 μm attains a constant settlement size of 706 ± 8 μm (mean ± SD). Retention of eye pigmentation in newly settled juveniles, along with the genetic panmixia, suggests that the hatched larva of ‘S.’briandimigrates vertically to the surface water, presumably to take advantage of richer food supplies and stronger currents for dispersal, as has been shown for confamilial species at hydrothermal vents and cold methane seeps.

Basal gastropods have various types of body appendages. Besides pallial or cephalic tentacles, subocular tentacles, neck lobes and (occasionally) copulatory structures, there are epipodial tentacles and epipodial sense organs (ESOs), which have often been confused in the past. We provide clear definitions of these two different epipodial structures, describe various examples and reconsider literature data on their occurrence throughout basal gastropod clades, i.e. Patellogastropoda, Cocculiniformia, Neritimorpha, Neomphalina and (in particular) Vetigastropoda. So-called 'epipodial tentacles' of Patellogastropoda, Cocculiniformia, Neomphalina and of several vetigastropod subgroups are considered to represent a distinct and apomorphic gastropod organ, the ESO. In contrast, true epipodial tentacles are probably serial or iterative homologues of cephalic tentacles and are restricted to Vetigastropoda and certain caenogastropod taxa. In the light of these new data and interpretations, an evolutionary scenario is presented for epipodial structures in basal gastropods: a single pair of ESOs in a posterior position is considered as an apomorphic character of the gastropod stem lineage, which is retained in early juvenile Patellogastropoda, many Cocculiniformia and early juvenile Vetigastropoda. The various conditions in Neomphalina and Vetigastropoda can be explained by considering modularity of ESOs, cephalic/epipodial tentacles and sensory papillae. Each of these modules has become serially repeated in evolution and occurs in various combinations among basal gastropod clades.

The gastropod superfamily Lepetelloidea represents an extremely diverse lineage in terms of their utilization of different deep-sea organic substrates that include sunken wood, leaves, whale and fish bones, egg cases of sharks and rays, annelid tubes and detrital cephalopod beaks among others. They also inhabit cold seeps and hydrothermal vents, thus presenting an interesting case for the evaluation of such organic substrates as stepping stones' into these chemosynthetically nourished environments. Here we show the first molecular phylogeny of the Pseudococculinidae, a primarily wood-dwelling family and the most speciose in Lepetelloidea. Special emphasis is placed on the genus Caymanabyssia, for which the only subfamily Caymanabyssiinae has been established, and a new species Caymanabyssia solis is described herein and compared with previously known taxa in order to reconsider the morphological characteristics of lepetelloids on wood. Bayesian and likelihood trees reconstructed using four-gene sequences reveal that Pseudococculinidae sensu auctt. is a polyphyletic taxon that is grouped by shared plesiomorphic conditions of characters including the radula, a digestive organ, the morphology of which is often governed strongly by diet and feeding ecology. The newly reinterpreted families Pseudococculinidae and Caymanabyssiidae represent reciprocal sister clades as a basal radiation in Lepetelloidea. Sunken wood might thus have served as an ancestral habitat from which species on other substrates and vent and seep taxa were derived.

A new genus and species of Cataegidae (Gastropoda; Seguenzioidea) from eastern Pacific Ocean methane seeps.

Energy availability has long been recognized as a predictor of community structure, and changes in both terrestrial and marine productivity under climate change necessitate a deeper understanding of this relationship. The productivity-diversity relationship (PDR) is well explored in both empirical and theoretical work in ecology, but numerous questions remain. Here, we test four different theories for PDRs (More-Individuals Hypothesis, Resource-Ratio Theory, More Specialization Theory, and the Connectivity-Diversity Hypothesis) with experimental deep-sea wood falls. We manipulated productivity by altering wood-fall sizes and measured responses after 5 and 7 years. In November 2006, 32 Acacia sp. logs were deployed at 3203 m in the Northeast Pacific Ocean (Station Deadwood: 36.154098 degrees N, 122.40852 degrees W). Overall, we found a significant increase in diversity with increased wood-fall size for these communities. Increases in diversity with wood-fall size occurred because of the addition of rare species and increases of overall abundance, although individual species responses varied. We also found that limited dispersal helped maintain the positive PDR relationship. Our experiment suggests that multiple interacting mechanisms influence PDRs.

Carbonate communities: The activity of anaerobic methane oxidizing microbes facilitates precipitation of vast quantities of authigenic carbonate at methane seeps. Here we demonstrate the significant role of carbonate rocks in promoting diversity by providing unique habitat and food resources for macrofaunal assemblages at seeps on the Costa Rica margin (400-1850 m). The attendant fauna is surprisingly similar to that in rocky intertidal shores, with numerous grazing gastropods (limpets and snails) as dominant taxa. However, the community feeds upon seep-associated microbes. Macrofaunal density, composition, and diversity on carbonates vary as a function of seepage activity, biogenic habitat and location. The macrofaunal community of carbonates at non-seeping (inactive) sites is strongly related to the hydrography (depth, temperature, O2) of overlying water, whereas the fauna at sites of active seepage is not. Densities are highest on active rocks from tubeworm bushes and mussel beds, particularly at the Mound 12 location (1000 m). Species diversity is higher on rocks exposed to active seepage, with multiple species of gastropods and polychaetes dominant, while crustaceans, cnidarians, and ophiuroids were better represented on rocks at inactive sites. Macro-infauna (larger than 0.3 mm) from tube cores taken in nearby seep sediments at comparable depths exhibited densities similar to those on carbonate rocks, but had lower diversity and different taxonomic composition. Seep sediments had higher densities of ampharetid, dorvilleid, hesionid, cirratulid and lacydoniid polychaetes, whereas carbonates had more gastropods, as well as syllid, chrysopetalid and polynoid polychaetes. Stable isotope signatures and metrics: The stable isotope signatures of carbonates were heterogeneous, as were the food sources and nutrition used by the animals. Carbonate δ13Cinorg values (mean = -26.98‰) ranged from -53.3‰ to +10.0‰, and were significantly heavier than carbonate δ13Corg (mean = -33.83‰), which ranged from -74.4‰ to -20.6‰. Invertebrates on carbonates had average δ13C (per rock) = -31.0‰ (range -18.5‰ to -46.5‰) and δ15N = 5.7‰ (range -4.5‰ to +13.4‰). Average δ13C values did not differ between active and inactive sites; carbonate fauna from both settings depend on chemosynthesis-based nutrition. Community metrics reflecting trophic diversity (SEAc, total Hull Area, ranges of δ13C and δ15N) and species packing (mean distance to centroid, nearest neighbor distance) also did not vary as a function of seepage activity or site. However, distinct isotopic signatures were observed among related, co-occurring species of gastropods and polychaetes, reflecting intense microbial resource partitioning. Overall, the substrate and nutritional heterogeneity introduced by authigenic seep carbonates act to promote diverse, uniquely adapted assemblages, even after seepage ceases. The macrofauna in these ecosystems remain largely overlooked in most surveys, but are major contributors to biodiversity of chemosynthetic ecosystems and the deep sea in general.

Large symbiont-hosting snails of the genus Alviniconcha (Gastropoda: Abyssochrysidae) are among the dominant inhabitants of hydrothermal vents in the Western Pacific and Indian oceans. The genus was originally described as monotypic, but unique DNA sequences for mitochondrial genes revealed six distinct evolutionary lineages that we could not distinguish based on external morphology. Subsumed under the name Alviniconcha hessleri Okutani & Ohta, the distinct allopatric and sympatric lineages have been assigned placeholder epithets that complicate scientific communications. Based on the present multi-gene sequence data, we hereby describe five Alviniconcha species (in the order of their discovery) - A. kojimai sp. nov., A. boucheti sp. nov., A. marisindica sp. nov., A. strummeri sp. nov. and A. adamantis sp. nov. Thus, we restrict application of the name A. hessleri to specimens that are genetically similar (>= 95% for COI) to those found at localities in the Mariana Trough. Single distinct Alviniconcha species inhabit vent fields along the Central Indian Ridge, the Mariana volcanic arc, and the Mariana back-arc basin, whereas vents in the Manus, Fiji and Lau back-arc basins may host two or three additional species. Formal recognition of these species facilitates future attempts to assess their physiological differences and symbiont associations. Furthermore, their reported distributions have significant biogeographic implications, affecting estimates of the diversity within and overlap among Indo-Pacific vent localities.[GRAPHICS]

The application to conserve the current usage of the name Cerithiopsis tubercularis (Montagu, 1803) for a species of cerithiopsine gastropod from the southern coast of Great Britain by designating a neotype consistent with current usage was not approved.

Bridging the Atlantic and Mediterranean continental margins, the South Iberian region has recently been the focus for geological and biological investigations. In this region, the Gulf of Cadiz (GoC) encompasses a great variety of deep-sea habitats that harbour highly diverse biological communities. In this study, we describe the composition of gastropod assemblages obtained from in situ colonization experiments and benthic sampling of deep-sea habitats in the GoC. Gastropod distributional patterns, such as bathymetric ranges, bathymetric turnover, affinity to substrate types and abundance-occupancy relationships, are analysed and interpreted in relation to their inferred dispersal capabilities and substrate availability. Overall, the GoC comprises a high diversity of gastropods (65 species), and distinct assemblages were found in typical sedimentary environments at mud volcanoes and in association with carbonate and coral samples or organic substrata. The number of taxa peaked at the Carbonate Province in the middle slope (600–1200 m depth), a highly heterogeneous area with numerous mud volcanoes, carbonate mounds and corals. Darwin (1100 m) and Captain Arutyunov (1300 m) mud volcanoes harboured the most species-rich and abundant gastropod assemblages, respectively. Colonization experiments with organic substrata (wood and alfalfa grass) also yielded diverse and abundant gastropod assemblages. These organic inputs allowed the recruitment of local species but mainly of wood specialist taxa that were not previously known from the GoC. Our results suggest that the distribution of gastropod assemblages may be primarily determined by the occurrence of suitable habitats, probably due to the effect of the substrate type on the structural complexity of the habitat and availability and diversity of adequate food sources. The type of larval development is apparently not a limiting factor for colonization of deep-sea habitats. However, the predominance of non-planktotrophy, and especially lecithotrophy, suggests that a trade-off between more limited dispersal capability and higher potential for self-recruitment may be a recurrent pattern in gastropod species inhabiting reducing environments and other patchily distributed deep-sea habitats. A network of suitable habitats that ensures effective population connectivity would explain the predominance and relatively wide distribution of short-distance dispersing non-planktotrophic species in the GoC deep-sea habitats and other geographical regions.

Yasunori Kano1, Hiroaki Fukumori1,2, Bastian Brenzinger3 and Anders Waren4 Department of Marine Ecosystems Dynamics, Atmosphere and Ocean Research Institute, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8564, Japan; Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan; Bavarian State Collection of Zoology, Munchhausenstr. 21, D-81247 Munich, Germany; and Swedish Museum of Natural History, Box 50007, SE-10405 Stockholm, Sweden

A new gastropod, Kaneconcha knorri gen et sp. nov., was found in marlstone dredged from the surface of Adam Dome at Kane Megamullion on the flank of the Mid-Atlantic Ridge in an area of former hydrothermal activity. The snail is interpreted as a large provannid similar to the chemosymbiotic genera Ifremeria and Alviniconcha. This is the first record of presumably chemosymbiotic provannids from the Atlantic Ocean and also the first fossil record of such large provannids associated with hydrothermal venting. Extant Alviniconcha and Ifremeria are endemic to hydrothermal vents in the Pacific and Indian oceans. Kaneconcha differs from Ifremeria in having no umbilicus and a posterior notch, and from Alviniconcha in having the profile of the whorl slightly flattened and having no callus on the inner lip. A dark layer covering the Kaneconcha shell is interpreted here as a fossilized periostracum. The shell/periostracum interface shows fungal traces attributed to the ichnospecies Saccomorpha clava. We hypothesize that large chemosymbiotic provannids (i.e. Kaneconcha, Ifremeria, and Alviniconcha) forma clade that possibly diverged from remaining provannids in the Late Jurassic, with the Late Jurassic/Early Cretaceous Paskentana being an early member.

Upon their initial discovery, hydrothermal vents and methane seeps were considered to be related but distinct ecosystems, with different distributions, geomorphology, temperatures, geochemical properties and mostly different species. However, subsequently discovered vents and seep systems have blurred this distinction. Here, we report on a composite, hydrothermal seep ecosystem at a subducting seamount on the convergent Costa Rica margin that represents an intermediate between vent and seep ecosystems. Diffuse flow of shimmering, warm fluids with high methane concentrations supports a mixture of microbes, animal species, assemblages and trophic pathways with vent and seep affinities. Their coexistence reinforces the continuity of reducing environments and exemplifies a setting conducive to interactive evolution of vent and seep biota.