Biology of Finfish and Shellfish

4.10.3. Veliger

The preoral ciliate area or velum begin to protrude on both sides as a bilobed flap. The velum are very delicate and extensive, and a very delicate organs of locomotion. Between the bases of velar lobes, the anterior end of the larva is provided with eyes and tentacles. The larva has a shell into which the velar apparatus could be withdrawn and which encloses the partly developed viscera. Alimentary canal is complete and the anus is shifted to anterior side. A foot usually bearing an operculum if present. In addition to velar apparatus, there are some organs like larval heart and kidney also present. The larval kidneys are paired and generally symmetrical organs situated at the anterior end of the body immediately behind the velum. Statocyst and gill-rudiments are also present. Some gastropods have feeding veligers with a larval life that may last as long as three months. Others have brief yolk-laden nonfeeding veliger. The long cilia of the velum function not only in locomotion but also in suspension feeding. During the course of the veliger stage, torsion occurs and the shell and visceral mass twist 180^o in relation to the head and foot.