|Pacific Blue Mussel|
Mussel sexes are separate. In the spring eggs and sperm are released into the water. The fertilized eggs develop into swimming larvae called veligers (veil bearing) in about 2 days. In another day the foot begin to appear. They are now called pedi-veligers. Does it make sense if you think about what a pedestrian is?
Drawings after Field I. A. 1921 Bull. Bureau Fish. 38:127-259
They are estimated to take about 5 to 7 weeks before the larvae settle down to the bottom--looking like miniature adults. At this stage the shell is transparent. You can directly see the gills moving food, the pumping heart, and the contracting muscles.