Eggs in both Ohio and Tennessee River water began dividing a little over 1 hour after fertilization and continued developing at a steady rate. Development up to the free-swimming trochophore stage successfully occurred in both Ohio and Tennessee River water. Since the introduction of this exotic mussel into North American waters, it has spread rapidly due in part to its unique life cycle. The zebra mussel is unusual among freshwater mollusks in having a free-swimming planktonic larval stage, similar to that of many marine bivalves. Zebra mussels are dioecious broadcast spawners, releasing their gametes in enormous quantities directly into the water column.
Fertilization occurs externally, with development following in the open water.
It is at this stage that ciliary development occurs and movement begins.