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Plant remains from land, particularly sunken wood, represent significant input of organic matter into the generally oligotrophic deep sea, leading to the formation of macrofaunal assemblages around them. Following the onset of decomposition by wood-boring bivalves, microbes and fungi the wood eventually becomes an anoxic and reducing environment attracting chemosynthetic fauna. Wood falls have primarily been studied by either opportunistic sampling by trawls or artificial deployments, while in situ observations of natural systems remain scarce. Here, we report a natural late-stage wood-fall community at 5505 m depth in the Northwestern Pacific abyssal plain by a manned submersible. Our observations revealed details in faunal distribution that cannot be obtained by trawled material, including the presence of associated xenophyophores. We identified a total of 26 animal species and one xenophyophore from the wood fall including both wood-associated and chemosymbiotic taxa, although cocculiniform limpets were conspicuously missing. Living xylophagaid bivalves were also not observed, but the wood was heavily burrowed and they were clearly once present. This rare finding improves our understanding of deep abyssal wood falls at the senescence stage, and highlights the importance of direct seafloor observations. [ABSTRACT FROM AUTHOR]

Recently, the species richness of provannid gastropods inhabiting chemosynthetic ecosystems in the northwestern Pacific has been reassessed, revealing a much higher diversity than previously realized. Here, we describe four further new species, two in the genus Desbruyeresia and two in the genus Provanna. Their generic placement was confirmed by both shell and radula morphology, as well as phylogenetic reconstruction using the mitochondrial cytochrome c oxidase subunit I gene. Desbruyeresia armata n. sp. from vent fields in the Izu-Ogasawara Arc is characterized by a stout shell with numerous tubercles or short spines and marginal teeth coarsely serrated into only four denticles. Desbruyeresia costata n. sp. from Okinawa Trough vents is distinguished from other congeners by an elongate shell with strong axial ribs and obsolete spiral ribs. These represent the first Desbruyeresia species from Japanese waters. Provanna fenestrata n. sp. discovered from two vent fields in the Okinawa Trough is instantly recognizable from its uniquely regular rectangular lattice sculpture; Provanna stephanos n. sp. is a surprising new discovery from the supposedly well-explored ‘Off Hatsushima’ hydrocarbon seep site in Sagami Bay, and is highly distinctive with two characteristic rows of strongly spinous spiral ribs. The discovery of these new species in relatively well-explored chemosynthetic ecosystems in Japan indicates that the biodiversity of such systems remains poorly documented.

We describe three Miocene species of Provanna from Japan, two new and one in open nomenclature, that represent the only known fossil examples from whale-falls and a considerable increase in the Miocene diversity of the genus. Provanna hirokoae sp. nov. comes from the latest Middle Miocene Kuroiwa seep site in central Honshu. The shells of this species are mostly recrystallized, but contain relict crossed lamellar microstructures. Provanna alexi sp. nov. is from the early Middle Miocene Shosanbetsu whale-fall site in northwestern Hokkaido, and has well preserved shells comprising an outer simple prismatic layer and an inner crossed lamellar layer. The two Provanna specimens from the Middle Miocene Rekifune whale-fall site, in eastern Hokkaido, are preserved as external moulds only, so are left in open nomenclature. Based on current knowledge, the presence of an outer prismatic layer and an underlying crossed lamellar layer seems to be a common feature in the shells of Provanna, as well as in other genera belonging to the family Provannidae and the superfamily Abyssochrysoidea. Although the oldest occurrence of Provanna was in the Late Cretaceous, the genus did not spread geographically and ecologically until the Miocene (with four, or possibly five species), a date concordant with some molecular estimates. However, this could be an artefact of the fossil record because the known pre-Miocene seep and whale-falls are more geographically restricted than those from the Miocene. [ABSTRACT FROM AUTHOR]

The genomic DNA of twoProvannasp. individuals was extracted, sequenced using an Illumina HiSeq1500, and the mitogenome was assembled. The nearly complete metogenome was 16,183 bp in length, consisting of 37 typical metazoan mitochondrial genes with the typical caenogastropod mitochondrial gene order. All mitochondrial genes were encoded on the heavy strand with the exception of eight transfer RNA genes. To reconstruct the phylogenetic position of the deep-sea Provannidae, we used amino acid sequences of all the 13 mitochondrial protein-coding genes in Bayesian inference, maximum likelihood, and maximum parsimony analyses with sequences of selected gastropods. The resultant phylogenetic trees supported the placement of Provannidae in the superfamily Abyssochrysoidea of the clade Littorinimorpha of Gastropoda, providing new data for understanding the phylogeny of these deep-sea snails. [ABSTRACT FROM AUTHOR]