In this study, characterization of DTHS3 satellite DNA (satDNA) was further expanded within the class Bivalvia. Monomer variants of DTHS3 satDNA were compared in 12 bivalve species belonging to two different subclasses, Heterodonta and Pteriomorphia. This satDNA, whose age is estimated to a minimum of 516 Ma, is contributing to the concept of the dual character of satDNA sequences: their sequence preservation throughout long evolutionary periods and generation of species-specific variants of the same satDNA family.