Dwarf Males in the Teredinidae (Bivalvia, Pholadacea)

Abstract
Extreme sexual dimorphism in the Bivalvia is rare. The occurrence of dwarf males inZachsiaappears to be the first case in the Teredinidae and the first outside the Leptonacea. FemaleZachsiarelease straight-hinge larvae that develop in the plankton and settle on living rhizomes ofPhyllospadix. Larvae entering mantle pouches of females become males. Evolution of this life history pattern is tied to problems of living in a fragile, patchy habitat—that is, the rhizomes ofPhyllospadix.