Overlooked for a long time, wood falls on the deep oceanic floor are now recognized as extreme, reducing ecosystems based on chemosynthesis, in the same way that hydrothermal vent, cold seeps and whale falls with which they share important physicochemical and faunistic similarities. In these ecosystems, bacterial chemosynthesis using reduced compounds (H2S, CH4) and/or digestion of refractory organic compounds (cellulose and lignin in wood, organic matrix of bone) by heterotrophic bacteria play an essential trophic role, and appear to promote establishment of mutualistic symbioses between bacteria and metazoans for the exploitation of environmental resources. Beyond the description of the taxonomic composition of fauna associated with these sites, current studies aim to understand the functioning and evolutionary links of these ecosystems. Digestive and/or chemoautotrophic associations with microorganisms that could be the key to survive in these habitats have been described in a number of molluscs and annelids but only few crustaceans. The latter distinguish from the other groups by the fact they do not realize intracellular symbioses (endosymbioses) but mainly carry ectosymbioses on their integument (epidermis and cuticle) even in the digestive tract that is partly lined by epidermis (in stomodeum and proctodeum). Moreover, up to now, nothing was known about crustaceans from deep-sea wood falls, their feeding habits and associations with microorganisms. The present work focused on the crustaceans and especially 15 species of decapods from wood falls in the South Pacific Ocean. The specimens were recovered during several French cruises (Salomon2, BOA1, SantoBOA, SalomonBOA3) organized near the Vanuatu, Solomon Island and New Caledonia by the Muséum National dHistoire Naturelle of Paris. The investigation of the feeding biology and microbial associations of the decapod species combined three complementary approaches : 1) a morphological approach using light and electron microscopy to describe the external and gut structures as well as the gut content and microflora, 2) a trophic approach based on stable isotopes analyses (C and N) together with the nature of the gut content and 3) a molecular approach based on 16S rRNA gene analyses and FISH labeling to identify and locate the bacteria in the gut content (ingested bacteria) and on the gut lining (resident bacteria or symbionts). Taxonomic identification and morphological observations of the species provided a first non-exhaustive inventory of the best represented decapod species in wood accumulations in the deep South Pacific and point out three interesting informations. 1) Most decapods from the sunken woods belong to Reptantia. 2) Some species (e.g. Munidopsis spp.) belong to deep sea taxa and exhibit typical characteristics while others (e.g. Xylopagurus) much more resemble shallow-water species, indicating that the colonization of wood falls by decapods may have occurred from both deep and coastal habitats. 3) Association degree with sunken wood could be important for some species that appear endemic (e.g. Pylochelidae, Xylopagurus) or which probably have their complete life cycle on wood falls (most of the gravid females having big eggs with a direct larval development). From a trophic point of view, morphological observations of the digestive system, examinations of gut contents and stable isotope analyses carried out on 15 species, allow us to classify the decapod crustacean from deep-sea sunken woods into two major groups, detritivores and predators/scavengers, and four trophic guilds (trophic levels) depending on two primary food sources, the wood and the particulate organic matrix (marine snow). The four guilds were identified as bacteriovorous detritivores (M. nitida, M. pilosa, M. bispinoculata, Munidopsis sp.1), xylophagous detritivores (M. andamanica, R. amboinensis), omnivores (X. caledonicus) and predators/scavengers (pylochelid species, Munida spp, Axiidae sp.1, M. cylindrophthalma). A fifth guild could be represented by limivorous detritivores (C. acutirostella, Alpheidae sp.1). This breaks with the widespread idea that decapod crustaceans from wood falls are all scavengers or predators. In addition, these results have evidenced of some special dietary strategies and highlight the importance of xylophagous decapods in the ecosystem, by their mechanical degradation of the substrate and their production of feces which should enrich the sediment and have a significant impact on the composition of wood and sediment microbiota (bacteria and fungi). Microscopic observations also allowed us to identify potentially symbiotic associations with resident (and transient) microorganisms (bacteria and/or trichomycetes) in the hindgut of five detritivorous species. Owing that, three of these species have a wood-based diet (M. andamanica, M. nitida, R. amboinensis) and considering the location of these microflora, it is strongly suggested that the resident microorganisms are directly related to the xylophagous diet of the host and most particularly involved in the digestion of wood. More detailed in two xylophagous species, M. andamanica and R. amboinensis, not only these microflora can be distinguished on the basis of their morphology, location and probable genetic differences but also by their roles and involvement in the digestion of the woody substrate. The digestive bacteria of M. andamanica could act as trophic intermediates while those of R. amboinensis probably only help in its digestion. From the stable isotopes ratio, it is likely that R. amboinensis directly assimilates the wood digestion products while M. andamanica feeds on wood with a trophic intermediate. Cloning and sequencing 16S rRNA gene from the gut bacteria of M. andamanica revealed its resident hindgut microflora is largely dominated by two phylotypes (OTUs) of possibly symbiotic bacteria that belong to Firmicutes and Alphaproteobacteria. Surprisingly, these OTUs are very close to gut bacteria isolated from a coastal thalassinid shrimp N. californiensis and from the Chinese crab E. sinensis. The results raise the question of the development and evolution of digestive symbioses in decapods and crustaceans in relation to the diet and/or adaptation to a special habitat, owing that among galatheid crabs the symbiotic relationships appear closer in certain species (M. andamanica) than in others (M. nitida, M. bispinoculata) and that similar differences appear between taxonomic groups. On the other hand, the genetic proximity of bacteria from distant crustacean species raise the question of an eventual co-evolution of linked hosts and symbionts contrasting with the permanent re-acquisition of symbionts from the medium.

The present study characterized the deep-sea gastropods community collected on whale bones and wood parcels artificially implanted in the deep Southwest Atlantic Ocean at 1500 and 3300 m depth for 23 months. A total of 5493 gastropods were collected and their distribution, abundance and diversity on substrates, depths and latitudes were calculated. Species richness and abundance of gastropods were higher in whale bones and deeper sites. Latitude did not seem to influence the distribution of mollusks. Five species were selected due to their abundance and possible ecological importance for further studies. Three were new species of the superfamily Abyssochrisoidea and were morphologically and genetically described (two Rubyspira and one Cordesia). The other two were Hyslogyrina rissoela (Heterobranchia) and Lusitanops cingulatus (Neogastropoda). To understand their feeding behavior and dispersal strategies were conduced stable isotopes analyzes, observations of gut content, and radular and larval shell morphology. Larval shell of most species suggested planktotrophic development. Animals on different growth stages were found. Gastropods presented a diversity of feeding strategies, such as bacterial mats grazing, predation and specialized bone eating. The overlap of this fauna with other chemosynthetic environments and with other basins corroborate with the ecological stepping stone hypothesis. Besides that, phylogenetic studies about Abyssochrysoidea were made. Their phylogenetic position within the Caenogastropoda are still uncertain but this group is considered closely related with Littorinidae. These snails are endemic from chemosynthetic environments, such as deep-sea hydrothermal vents, cold seeps and organic falls in the deep-sea. The genus Rubyspira is not settled at family level and no molecular studies were made for Cordesia. The present study also attempts to assign these groups phylogenetically. Concatenated COI, 16S, 18S and 28S and individual gene trees were constructed for maximum likelihood and Bayesian analysis. In all analyses the family Newtoniellidae were a sister group of Abyssochrysoidea. Morphological and genetic evidences suggest that Rubyspira and Cordesia are closer related to Abyssochrysos than to other provannid snails. The most accepted hypothesis is that Provannidae is paraphyletic. However, there are other ideas that indicates Rubyspira and Cordesia could be included in Abyssochrysidae or the Provannidae should be considered Abyssochrysidae. A morphologic revision of the superfamily should be made to better understand the relation within the group. Clades within the Abyssochrysoidea were always well supported and similar to those found in the literature. The position of Rubyspira and Cordesia within Abyssochrysoidea suggest whale bones and wood parcels did not play an evolutionary role as stepping stones for this group. / O presente estudo caracterizou a comunidade de gastrópodes de mar profundo coletados em carcaças de baleia e parcelas de madeira artificialmente implantadas no Sudoeste do Oceano Atlântico profundo a 1500 e 3300 m de profundidade por 23 meses. Um total de 5493 gastrópodes foram coletados e sua distribuição, abundância e biodiversidade nos substratos, profundidades e latitudes foram calculados. A riqueza e abundância dos gastrópodes foi maior nos ossos de baleia e em maiores profundidades. A latitude parece não ter influenciado na distribuição dos moluscos. Cinco espécies foram selecionadas devido à abundância e possível importância ecológica. Três são novas espécies da superfamília Abyssochrysoidea que foram descritas morfologicamente e filogeneticamente (duas Rubyspira e uma Cordesia). As outras duas foram Hyalogirina rissoela (Heterobranchia) e Lusitanops cingulatus (Neogastropoda). Para compreender os hábitos alimentares e de dispersão desses animais análises de isótopos estáveis, observações do conteúdo do trato digestório, da morfologia das rádulas e das conchas larvais foram realizadas. A concha larval da maioria das espécies sugere um desenvolvimento planctotrófico. Os moluscos encontrados apresentaram diversos tipos de hábitos alimentares como raspadores de carpete bacteriano, predadores e especialistas de ossos. A sobreposição dessa fauna com a de outros ambientes quimiossintéticos e de outras bacias oceânicas colabora com a hipótese ecológica das \"stepping stones\" no mar profundo. Além disso, estudos sobre a posição filogenética dos Abyssochrysoidea foi feita. Sua posição nos Caenogastropoda ainda é incerta, mas são considerados próximos aos Littorinidae. Esses animais são endêmicos de ambientes quimiossintéticos, como fontes hidrotermais de mar profundo, fontes frias e quedas orgânicas. O gênero Rubyspira não está atribuído à nenhuma Família e não foram realizados estudos moleculares para Cordesia. Esse estudo também tenta organizar esses grupos filogeneticamente. Árvores concatenadas e individuais dos genes COI, 16S, 18S e 28S foram construídas para máxima verossimilhança e análise bayesiana. Em todos resultados a família Newtoniellidae foi um grupo irmão dos Abyssochrysoidea. Evidências morfológicas e genéticas s para que sugerem que Rubyspira e Cordesia então mais próximos dos Abyssochrysos do que de outros provannides. A teoria mais aceita é de que os Provannidae são parafileticos. Porém há outras ideias de que Rubyspira e Cordesia poderiam ser inclusos em Abyssochrysidae, ou que os Provannidae fossem considerados Abyssochrysidae. Uma revisão dessa superfamilia deveria se feita para entender as relações desse grupo. Os clados de Abyssochrysoidea sempre foram bem suportados como na literatura. A posição de Rubyspira e Cordesia nos Abyssochrysoidea. aponta que os ossos de baleia e parcelas de madeira possam não terem servido como \"stepping stones\" evolutivas para esses gastrópodes.

The present study characterized the deep-sea gastropods community collected on whale bones and wood parcels artificially implanted in the deep Southwest Atlantic Ocean at 1500 and 3300 m depth for 23 months. A total of 5493 gastropods were collected and their distribution, abundance and diversity on substrates, depths and latitudes were calculated. Species richness and abundance of gastropods were higher in whale bones and deeper sites. Latitude did not seem to influence the distribution of mollusks. Five species were selected due to their abundance and possible ecological importance for further studies. Three were new species of the superfamily Abyssochrisoidea and were morphologically and genetically described (two Rubyspira and one Cordesia). The other two were Hyslogyrina rissoela (Heterobranchia) and Lusitanops cingulatus (Neogastropoda). To understand their feeding behavior and dispersal strategies were conduced stable isotopes analyzes, observations of gut content, and radular and larval shell morphology. Larval shell of most species suggested planktotrophic development. Animals on different growth stages were found. Gastropods presented a diversity of feeding strategies, such as bacterial mats grazing, predation and specialized bone eating. The overlap of this fauna with other chemosynthetic environments and with other basins corroborate with the ecological stepping stone hypothesis. Besides that, phylogenetic studies about Abyssochrysoidea were made. Their phylogenetic position within the Caenogastropoda are still uncertain but this group is considered closely related with Littorinidae. These snails are endemic from chemosynthetic environments, such as deep-sea hydrothermal vents, cold seeps and organic falls in the deep-sea. The genus Rubyspira is not settled at family level and no molecular studies were made for Cordesia. The present study also attempts to assign these groups phylogenetically. Concatenated COI, 16S, 18S and 28S and individual gene trees were constructed for maximum likelihood and Bayesian analysis. In all analyses the family Newtoniellidae were a sister group of Abyssochrysoidea. Morphological and genetic evidences suggest that Rubyspira and Cordesia are closer related to Abyssochrysos than to other provannid snails. The most accepted hypothesis is that Provannidae is paraphyletic. However, there are other ideas that indicates Rubyspira and Cordesia could be included in Abyssochrysidae or the Provannidae should be considered Abyssochrysidae. A morphologic revision of the superfamily should be made to better understand the relation within the group. Clades within the Abyssochrysoidea were always well supported and similar to those found in the literature. The position of Rubyspira and Cordesia within Abyssochrysoidea suggest whale bones and wood parcels did not play an evolutionary role as stepping stones for this group. / O presente estudo caracterizou a comunidade de gastrópodes de mar profundo coletados em carcaças de baleia e parcelas de madeira artificialmente implantadas no Sudoeste do Oceano Atlântico profundo a 1500 e 3300 m de profundidade por 23 meses. Um total de 5493 gastrópodes foram coletados e sua distribuição, abundância e biodiversidade nos substratos, profundidades e latitudes foram calculados. A riqueza e abundância dos gastrópodes foi maior nos ossos de baleia e em maiores profundidades. A latitude parece não ter influenciado na distribuição dos moluscos. Cinco espécies foram selecionadas devido à abundância e possível importância ecológica. Três são novas espécies da superfamília Abyssochrysoidea que foram descritas morfologicamente e filogeneticamente (duas Rubyspira e uma Cordesia). As outras duas foram Hyalogirina rissoela (Heterobranchia) e Lusitanops cingulatus (Neogastropoda). Para compreender os hábitos alimentares e de dispersão desses animais análises de isótopos estáveis, observações do conteúdo do trato digestório, da morfologia das rádulas e das conchas larvais foram realizadas. A concha larval da maioria das espécies sugere um desenvolvimento planctotrófico. Os moluscos encontrados apresentaram diversos tipos de hábitos alimentares como raspadores de carpete bacteriano, predadores e especialistas de ossos. A sobreposição dessa fauna com a de outros ambientes quimiossintéticos e de outras bacias oceânicas colabora com a hipótese ecológica das \"stepping stones\" no mar profundo. Além disso, estudos sobre a posição filogenética dos Abyssochrysoidea foi feita. Sua posição nos Caenogastropoda ainda é incerta, mas são considerados próximos aos Littorinidae. Esses animais são endêmicos de ambientes quimiossintéticos, como fontes hidrotermais de mar profundo, fontes frias e quedas orgânicas. O gênero Rubyspira não está atribuído à nenhuma Família e não foram realizados estudos moleculares para Cordesia. Esse estudo também tenta organizar esses grupos filogeneticamente. Árvores concatenadas e individuais dos genes COI, 16S, 18S e 28S foram construídas para máxima verossimilhança e análise bayesiana. Em todos resultados a família Newtoniellidae foi um grupo irmão dos Abyssochrysoidea. Evidências morfológicas e genéticas s para que sugerem que Rubyspira e Cordesia então mais próximos dos Abyssochrysos do que de outros provannides. A teoria mais aceita é de que os Provannidae são parafileticos. Porém há outras ideias de que Rubyspira e Cordesia poderiam ser inclusos em Abyssochrysidae, ou que os Provannidae fossem considerados Abyssochrysidae. Uma revisão dessa superfamilia deveria se feita para entender as relações desse grupo. Os clados de Abyssochrysoidea sempre foram bem suportados como na literatura. A posição de Rubyspira e Cordesia nos Abyssochrysoidea. aponta que os ossos de baleia e parcelas de madeira possam não terem servido como \"stepping stones\" evolutivas para esses gastrópodes.