Relationships between deep-sea invertebrates and bacterial symbionts, fueled by sulfide and methane, are well known, yet factors influencing symbiont specificity remain cryptic. For animals that obtain their symbionts from the environment, both host identity and geographic location can impact the ultimate symbiont partner. Bacterial symbionts were analyzed for 3 co-occurring species each of Bathymodiolus mussels and vestimentiferan tubeworms, from three deep methane seeps off the west coast of Costa Rica. The bacterial internal transcribed spacer...