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Veliger
A veliger is the planktonic larva of many kinds of sea snails and freshwater snails, as well as most bivalve molluscs (clams) and tusk shells.
== Description ==
The veliger is the characteristic larva of the gastropod, bivalve and scaphopod taxonomic classes. It is produced following either the embryonic or trochophore larval stage of development. In bivalves is sometimes referred to as a D-stage (early in its development) or pediveliger (late in its development) larva. This stage in the life history of these groups is a free-living planktonic organism; this mode of life potentially enhances dispersal to new regions far removed from the adult mollusks that produced the larvae.
The general structure of the veliger includes a shell that surrounds the visceral organs of the larva (e.g., digestive tract, much of the nervous system, excretory organs) and a ciliated velum that extends beyond the shell as a single or multi-lobed structure used for swimming and particulate food collection. The larva may have, or may develop, a foot that will be used by the newly settled veliger as it moves about and searches for an appropriate place to metamorphose.
Following metamorphosis, the foot may be used by the juvenile mollusk to move about on the seabed (in gastropods) or in the seabed (in some bivalves). The velum and foot of the veliger can be retracted into the shell to protect these structures from predators or mechanical damage.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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