Mussels have bluish-black shells that look like a flattened teardrop. The inside of the shell is pearly violet to white. Projecting from between the shells on the flat side is a bundle of tough, brownish threads, which are used to anchor themselves to hard surfaces. Inshore waters support the native Blue Mussel, which can reach 9 cm in length.
The wave-swept rocky west coast shores have beds of the larger Giant Pacific Mussel, which can grow to 25 cm in length. The mussels in the bottom photo are giant mussels. The Blue mussel has a smooth outer shell surface with growth rings, while the Giant Pacific Mussel has raised radial ribs.
A mussel is a type of bivalve mollusk that can be found where the ocean meets the shore. Like many other shellfish, they are cultivated and caught in the wild to serve as food for humans, and they also have a number of predators in the natural environment.
They share many characteristics with clams, another bivalve widely eaten by humans. They have a more oblong than an oval shell, however, with the dorsal region located towards the bottom of the shells rather than in the middle, as is common with clams. Mussels typically have a dark shell, in blue, green, or brown. A mussel that has anchored itself to a hard surface can be very difficult to dislodge.
These mollusks reproduce sexually, with the young hatching loose in the water. The larvae float until they reach a suitable living space, which distributes them more widely and gives them a better chance at survival. The primary diet of a mussel is plankton, along with other shellfish, They are filter feeders, sucking in water and filtering out nutrients to eat.