The veliger larva of Hydrobia ulvae with observations on the veliger of Littorina littorea (Mollusca: Prosobranchia)

The veliger larva of Hydrobiu ulvue (Pennant) from the west coast of Wales is described and illustrated from veligers hatched in the laboratory and collected in plankton samples. The larvae are planktotrophic and it is estimated that the pelagic phase is of about four weeks duration. In terms of density they form an important constituent of the plankton of inshore waters. The veliger larva of Littorina littoreu (L.) is also described and illustrated, and it is suggested that some of the conflicting reports on the length of the pelagic phase of H. ulvae result from confusion in indentification of the larvae of these two species.