The veliger larva has a shell and ciliated velum. Species that inhabit estuaries sometimes produce veliger larvae. The veliger is the characteristic larva of the gastropod, bivalve and scaphopod taxonomic classes. Mortality in this transitional stage from planktonic veliger to settled juveniles may exceed 99%. In species with a larval stage, the veliger is exclusively aquatic. The veliger larva feed on phytoplankton in the sea-water column. Unlike the adult, however, the veliger has two ciliated semi-circular structures resembling fins or wings. The veliger continues to mature forming the prodissoconch II shell. The veliger matures, and under certain conditions may experience sexual reversal.