Speciation of freshwater mussels (Bivalvia: Unionoidea) can occur symp
atrically (ecologically) via new glochidial host acquisition. Due to t
he characteristics of the unionoidean life cycle, this hypothesis over
comes the objections of the classical allopatric speciation paradigm,
namely homogamy and linkage of mate and habitat preferences. Examples
of freshwater mussel populations in various stages of the speciation p
rocess are provided from the literature.