The Yeti crab, Kiwa hirsuta Macpherson et al., is the single known species in a recently discovered crab family Kiwaidae (Decapoda: Galatheoidea) from deep-sea hydrothermal vents. Its chelipeds, walking legs and the ventral surface of its cephalothorax are covered with dense setae that, in turn, are covered with clusters of filamentous bacteria, making the crab appear extraordinarily 'hairy'. Electron microscopy revealed dense bacterial clusters attached to the chitinous outer layer of the setae. Molecular phylogenetic analyses revealed the setae-associated bacteria to be dominated by epsilon-Proteobacteria ( approximately 56% of the recovered ribotypes), gamma-Proteobacteria ( approximately 25%) and Bacteroidetes ( approximately 10%). Fluorescence in situ microscopy confirmed the attachment of filamentous epsilon-Proteobacteria on setae, but no specialized morphological structures appeared to exist for bacterial attachment. Key enzymes involved in the reductive tricarboxylic acid cycle (ATP-dependent citrate lyase) and sulfite oxidation or dissimilatory sulfate reduction (bidirectional APS reductase) were detected. Consequently, the potential for carbon fixation and cycling of reduced and oxidized sulfur appear to exist in the dense microflora that grows on the crab's setae.