Late Quaternary (Eemian) deposits of the Netherlands contain shells that resemble those of living Mytilus galloprovincialis . Similar broad-shelled mytilids also occur in estuaries of the southwestern Netherlands together with slender individuals typical of M . edulis . We sampled living mussels along a depth gradient in the Oosterschelde to a) investigate whether a relation exists between shell shape and depth, b) test if the broadshelled specimens might represent M . galloprovincialis (or a hybrid with M . edulis ) and c) assess by inference if the Quaternary specimens might be attributed to M . galloprovincialis as well. In order to do so, we compared genetic (length polymorphism of Me 15/16 , COIII sequences and AFLPs) and shellmorphological characteristics (juvenile L/W ratios and socalled Verduin parameters) of the same specimens. The obtained dataset indicates that all studied mussels from the Oosterschelde should be attributed to M . edulis , including those with broad shell outlines. No correlation of shell-morphology and depth-distribution was found. The worn and generally damaged state of the Eemian specimens precluded measurement of the Verduin parameters, while juvenile L/W ratios turned out not to be diagnostic. Therefore the shell characters examined in this study are insufficient to demonstrate the possible presence of M . galloprovincialis shells in Quaternary deposits of the Netherlands.