Introduction to mussels
Mussels are members of the Class Bivalvia, the second largest class of the phylum Mollusca.
As the name implies, bivalves have a two part shell (two valves), joined together dorsally by a hinge ligament. Bivalves, like all molluscs, have a mantle that encloses most of the visceral organs, and a muscular foot.
Ecology and physiology
Mussels live in fresh water (e.g., rivers and lakes) and salt water (e.g., intertidal, estuary, deep-sea) habitats.
Most mussels are filter feeders. But those specialized to live in deep-sea hydrothermal vent environments also obtain nourishment from symbiotic bacteria. A deep-sea vent mussel obtains raw materials (i.e., oxygen, carbon dioxide, and reduced chemicals like hydrogen sulfide) from the environment; it supplies these to chemosynthetic bacteria living in its tissues. Using the chemicals supplied by the mussel, the bacteria create sugars that provide the majority of nutrition for the mussel. Where inside the mussel do you suppose the bacteria live?