Bivalves: Bivalvia

Physical characteristics: The valves are narrowly triangular in shape and pointed at the front end. At the rear, the valves are smooth and appear swollen. They are alternately banded with dark brown and cream, suggesting a "zebra" pattern. Mature adults have valves about 2 inches (50 millimeters) long.

Geographic range: This species was first known from the Black and Caspian Seas. It has since been introduced into the canals and inland waterways of Western Europe. In the past twenty years it has also become established in the Great Lakes, on the Mississippi River, and in other major river systems in the United States.

Habitat: Zebra mussels lives on the bottom and attaches to rocks, wood, boats, and other hard surfaces at depths down to 195 feet (60 meters). Populations may contain one hundred thousand individuals per square yard (meter).

Diet: They eat plankton.

This species was first known from the Black and Caspian Seas. It has since been introduced into the canals and inland waterways of Western Europe. In the past twenty years it has also become established in the Great Lakes, on the Mississippi River, and in other major river systems in the United States. (Ed Reschke/Peter Arnold, Inc.)

Behavior and reproduction: Smaller mussels can detach themselves and move around, but larger individuals cannot. This species is introduced to new bodies of water by ships releasing water containing mussel larvae.

Both males and females are required for reproduction. A single female can release as many as forty thousand to one million eggs into the water each season. The veligers live among plankton, but eventually settle on hard surfaces after eighteen to twenty-eight days. Total life span is about two years.

Zebra mussels and people: Introduction of this species into waterways in Europe and North America has clogged the pipes of power plants and irrigation systems. They also threaten native bivalve populations by eating all of the available food and taking up living space.

Conservation status: Zebra mussels are not considered threatened or endangered. ∎