The Portuguese oyster Crassostrea angulata and the Japanese oyster Crassostrea gigas were described as distinct species with widely separated geographical origins - southwestern Europe and Japan respectively. In the 1970's C. gigas was introduced to the Atlantic coast of France in order to restore oyster farming affected by a disease of C. angulata, and it became evident that the two species could hybridize (Menzel, 1974, Huvet et al., 2004) and therefore were treated as synonyms (Huber, 2010). During the recent years, however, several genetic studies based on mitochondrial DNA and microsatellite data have provided evidence that the two taxa are genetically distinct although closely related (see overview in Batista et al. 2005). Particularly, an average of 2.3% difference in CO1 sequence suggests that populations of C. gigas and C. angulata may have diverged several hundred thousand years ago (Hedgecock et al., 2004). Studies involving microsatellite markers have shown that there are low but clear genetic differences between the two taxons. From all recent studies, it seems clear that the European C. angulata was introduced in the XVI or XVIIth century from Taiwan, and can be recognized genetically from C. gigas introduced later from Japan. Nevertheless the relationship of both taxa in intermediate locations remains to be elucidated. Lapègue et al. (2004) reported characteristic haplotypes of both C. gigas and C. angulata occurred in a population from northern China locally known as C. talienwhanensis Crosse, 1862; this could either mean that both species are distinct but overlap ranges, or that all those haplotypes are to be found in a single, geographically variable species. Considering this state of the art, C. angulata and C. gigas are listed here separately but qualified as very closely related and still possibly conspecific.