The zebra mussel is a small shellfish. It is a bivalve mollusc, a type called a mussel.
Color patterns vary, with only dark or colored shells or no stripes. They are typically found attached to objects, surfaces, or each other by threads underneath the shells. Although similar in appearance to the quagga mussel, the two species can be easily distinguished. When placed on a surface zebra mussels are stable on their flattened underside while quagga mussels, lacking a flat underside, will fall over.