veligers

A veliger is a free-swimming larval stage of many mollusks, arising after the trochophore stage and preceding settlement into a juvenile snail or clam. Veligers occur in most marine gastropods and bivalves; some groups may exhibit related larval forms, while others have direct development.

The velum is a pair of ciliated, lobed membranes used for swimming and feeding. A shell rudiment begins to form during the veliger, with growth of one or more valves as the larva develops; the foot is typically underdeveloped during this stage and expands later during metamorphosis. The veliger represents a transitional morphology between larval and juvenile forms.

Development typically proceeds from fertilized eggs to trochophore larvae, then to veligers, and finally to metamorphosed juveniles. Veligers may be planktotrophic, feeding on plankton, or lecithotrophic, relying on yolk. Metamorphosis is often triggered by environmental cues such as substrate, temperature, or salinity, at which point the velum is reduced and the juvenile shell and foot take on a more advanced form.

Ecology and significance: the planktonic veliger stage enables dispersal and connectivity among populations, influencing distribution and recruitment patterns. The duration of the veliger phase varies by species and environmental conditions, and it is sensitive to changes in temperature, salinity, and predation.

In research and aquaculture, veligers are central to culturing bivalves and gastropods, including oysters and mussels. Their morphology and development are also important for taxonomy, and larval shells provide information in the fossil record for paleontological studies.