Marine ecology: Do mussels take wooden steps to deep-sea vents?

Symbiont-containing mussels (Mytilidae) are found at hydrothermal vents and cold seeps on the ocean floor, but it is not known whether these taxa represent an ancient lineage endemic to these surroundings or are more recent invaders. Here we show that several small and poorly known mussels, commonly found on sunken wood and whale bones in the deep sea, are closely related to vent and seep taxa, and that this entire group is divergent from other Mytilidae. Our results indicate that vents and seeps were recently invaded by modern mytilid taxa and suggest that decomposing wood and bone may have served as 'steps' for the introduction of mytilid taxa to vents and seeps.