Two main morphotypes are typically found in Europe. Here we refer to morphotypes R (“round
form”) and S (“saddle form”) (Mouthon 2000;Pfenninger et al. 2002) that have usually been
respectively identified as C. fluminea and C. fluminalis. However, this nomenclature does
not satisfactorily reflect the taxonomic situation in the genus Corbicula in Western Europe
(Renard et al. 2000; Pfenninger et al. 2002). The shell surface of forms R and S has well-marked
concentric ridges that are more closely spaced and thinner in form S than in form R (Figure 1).
Form R is round and broad, while form S is narrow. Generally, form R reaches larger sizes