Adipicola pacifica are deep-sea bathymodiolin mussels associated with whale falls, living attached to exposed whale bones. Bathymodiolin mussels thrive in reducing environments such as around hydrothermal vents and hydrocarbon seeps, on whale falls, and on sunken wood. They have symbiotic relationships with chemoautotrophic and/or methanotrophic proteobacteria on which they rely for their nutrition, although some may also be facultative filter feeders. A range of evidence suggests that mussel species living around present-day vents and seeps are derived from ancestors associated with ancient animal falls, with these animal fall mussels themselves derived from lineages associated with sunken wood. (Fujiwara et al. 2010 and references therein)
Fujiwara et al. (2010) found that symbiosis in A. pacifica was extracellular. Most bacteria were located on the apical surfaces of epithelial cells in lateral zones of ctenidial (gill) filaments, although some were found within vacuoles of ctenidial cells, as is the case for intracellular symbionts. Although Fujiwara et al. suggest that A. pacifica may acquire some food by filter feeding, they note that they found these mussels only on nutrient-rich bone surfaces. They never found them on depleted bones or substrates around the whale carcasses, despite the fact that many suspension feeders such as Heteralepas barnacles, cirripeds, crinoids, cnidarians, and the benthic ctenophore Lyrocteis imperatoris occurred on these microsites. The absence of A. pacifica from these sites suggests that filter feeding is not the primary mode by which these mussels obtain food. (Fujiwara et al. 2010 and references therein)
