Freshwater Mussels of the French Creek Watershed

Mollusks are any one of a group of animals having no back bone (invertebrate), soft bodies not composed of segments, and are usually covered with a hard shell of one or more parts. A mussel is a type of mollusk with two outer shells hinged together. The hard shell is used as protection from potential predators that want to consume the soft tissue found within the shell.

Mussels are filter feeders, sucking in water and food through specialized structures call siphons. Because they are filter feeders, mussels are especially sensitive to any pollutants within the water. For example, if a barrel of oil spills into a creek, the mussels downstream will eventually take the oil into their bodies. Of the approximately 25 species of mussels found in the French Creek watershed, the Northern Riffle Shell, Clubshell, Rayed Bean, and Snuffbox are federally listed as endangered. Also, 18 of the species of mussels in French Creek are very rare and are currently being watched carefully.

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Because mussels are filter feeders, they do not have to move around to catch their food. Thus, mussels remain relatively stationary. A retractable appendage called a muscular food is responsible for the mussel’s movement. When a mussel feels it’s in danger, the foot is quickly retracted within the shell to protect itself from predators. The mussel reproductive system is very unique, because the juvenile stage is parasitic on fish. Larva called glochidia attach themselves to the gills and fins of a fish host. The fish’s tissue reacts by growing around the glochidia. After several weeks, the parasitic larval form is released and develops into free-living clams.

Mussels use gills, like fish, to breathe underwater. The water taken in through the siphons for food passes through their gills to deliver the oxygen they need to survive. The gills are thin, plate-like structures that remove the oxygen that is dissolved in the water. A mussel can be identified by its outer shell. Mussel shells within the same species closely resemble one another.