Document Type



Virginia Institute of Marine Science

Publication Date



Bulletin of Marine Science





First Page


Last Page



Many bivalve mollusks have one or more separate post-metamorphic stages which are functionally distinct from the late juvenile or the adult. The benthic plantigrade and the planktonic postlarva are defined and reviewed here. The plantigrade is a developmentally obligatory stage in mast bivalves. Various anatomical or conchological features, depending on taxa, are intermediate between the veliger and the juvenile. The plantigrade is benthic but highly mobile, via the foot and byssus, relative to the adult, although in some highly mobile bivalves, the plantigrade is functionally similar to the adult. The plantigrade may enter the water column briefly, but not nearly to the extent that the postlarva does. The planktonic postlarva is a non-obligatory stage, usually developmentally synonymous with the plantigrade, but functionally distinct. A specialized byssus or similar drogue is used by the postlarva for extended planktonic drifting. The plantigrade may serve simply as a developmentally intermediate stage between the larva and the juvenile, it may increase a species' options when selecting a habitat by its ability to relocate, or it may occupy a different habitat than later stages. The planktonic postlarva can either increase the dispersal ability of a bivalve, or, like the plantigrade phase, it can permit an ontogenetic niche shift. Planktonic postlarvae for three species not previously shown to exhibit this phase (Anadara transversa, Geukensia demissa, and Tellina agilis) are reported and described here.


Post-Larval Mussel; Macoma-balthica L; Mytilus-fdulis-L; Wadden Sea;