Wood falls in the deep sea have recently become the focus of studies showing their importance as nutrients on the deep-sea Xoor. In such environments, Crustaceans constitute numerically the second-largest group after Mollusks. Many questions have arisen regarding their trophic role therein. A careful examination of the feeding appendages, gut contents, and gut lining of Munidopsis andamanica caught with wood falls revealed this species as a truly original detritivorous species using wood and the bioWlm covering it as two main food sources. Comparing individuals from other geographic areas from substrates not reported highlights the galatheid crab as specialist of refractory substrates, especially vegetal remains. M. andamanica also exhibits a resident gut microXora consisting of bacteria and fungi possibly involved in the digestion of wood fragments. The results suggest that Crustaceans could be fullXedged actors in the food chains of sunken-wood ecosystems and that feeding habits of some squat lobsters could be diVerent than scavenging.

Even though their occurrence was reported a long time ago, sunken wood ecosystems at the deep-sea floor have only recently received specific attention. Accumulations of wood fragments in the deep sea create niches for a diverse fauna, but the significance of the wood itself as a food source remains to be evaluated. Pectinodonta sp. is a patellogastropod that exclusively occurs on woody substrates, where individuals excavate deep depressions, and is thus a potential candidate for a wood-eating lifestyle. Several approaches were used on Pectinodonta sampled close to Tongoa island (Vanuatu) to investigate its dietary habits. Host carbon is most likely derived from the wood material based on stable isotopes analyses, and high cellulase activity was measured in the digestive mass. Electron microscopy and FISH revealed the occurrence of two distinct and dense bacterial communities, in the digestive gland and on the gill. Gland-associated 16S rRNA gene bacterial phylotypes, confirmed by in situ hybridization, included members of three divisions (Alpha- and Gammaproteobacteria, Bacteroidetes), and were moderately related (90-96% sequence identity) to polymer-degrading and denitrifying bacteria. Gill-associated phylotypes included representatives of the Delta- and Epsilonproteobacteria. The possible involvement of these two bacterial communities in wood utilization by Pectinodonta sp. is discussed.

Squat lobsters of the deep-sea genus Munidopsis are among the most regularly reported crustaceans associated with deep-sea wood falls. They are often thought to indirectly use these substrates for preying or scavenging wood-associated molluscs or annelids, albeit the species M. andamanica has been recently highlighted as a xylophagous specialist. In this work, we examined the feeding appendages, gut contents and gut lining of M. nitida, M. bispinoculata and M. pilosa specimens from natural sunken woods and compared them with specimens of the same species having survived and grown on different hardto-digest substrates (i.e. woods, turtle shells and whale bones) experimentally submerged in the deep South Pacific. In both cases, all three species directly ingest large wood fragments deeply degraded by microorganisms, but M. nitida also feeds on experimentally submerged whale bone and turtle shell fragments. Munidopsis nitida is also the only species to host a resident gut microflora, but the bacterial morphotypes vary according to the ingested substrate. The results suggest that the three species are most probably opportunistic, bacterivorous detritivores and that M. nitida could be at the beginning of an evolutionary process towards xylophagy within the genus Munidopsis.