MEPS 295:183-190 (2005)  -  doi:10.3354/meps295183

ABSTRACT: The discovery and exploration of hydrothermal vents on the Central Indian Ridge (CIR) yielded invaluable samples for further resolution of the biogeography of chemoautotrophic symbioses. Mytilid mussels were collected from 2 CIR hydrothermal vent fields and preliminary molecular analyses suggested phylogenetic affinity with the western Pacific vent mussel Bathymodiolus brevior. Resolving whether this mussel, designated B. aff. brevior, hosts a dual symbiosis, as characterized for the 2 Mid-Atlantic Ridge hydrothermal vent mussel species, or a single chemoautotrophic symbiosis, as seen in the Pacific vent mussel species, will provide insight into the evolutionary history of mytilid symbioses. Ultrastructural, physiological, and molecular evidence are reported herein which support the presence of a single endosymbiont phylotype with chemoautotrophic metabolism. Phylogenetic analyses placed this symbiont in the same clade as the vesicomyid clam symbionts, prompting discussion regarding the evolutionary origin of chemoautotrophic symbioses in vent bivalves.

KEY WORDS: Chemoautotrophic endosymbiosis · Central Indian Ridge · Hydrothermal vent · Bathymodiolus spp.