Mussel
One of the many animals living at hydrothermal vents is the mussel Bathymodiolus. Shallow water mussels feed on plankton. Bathymodiolus however, has a different strategy — it lets Bacteria work for it.

These Bacteria live inside the gills of the animal. A steady flow of water across the gills delivers nutrients and energy sources to the symbiotic bacteria. Which in turn synthesize nutrients for their host.

Frontal view of one gill of Bathymodiolus,showing the ciliated part of the gill filaments. The beating cilia pump water across the gill.