Abstract
The taxonomy of species belonging to the genus Corbicula is complicated due to the individuals’ numerous high variations in shell shapes and colors. C. fluminea is native to continental Asia outside Japan and is known to include 2 different morphotypes. One has a white inner shell surface with purple highlights and was reported to occur in 1988 in Kurashiki, Okayama Prefecture, Japan, while the other sports a deep purple inner shell surface and is difficult to distinguish morphologically from Japanese C. leana. In recent years, individuals showing a close morphological similarity to C. leana have rapidly spread in the same area. This study was undertaken to genetically identify these individuals based on their molecular taxonomy. Nucleotide sequences of the mitochondrial region encoding the 16S ribosomal RNA gene generated only 2 haplotypes from a total of 24 freshwater Corbicula specimens including C. leana-like individuals and white inner C. fluminea morphotype individuals collected in September 2008 at a lower reach of the Takahashi River, whereas their shell morphology markedly varied. Multiple sequence analysis and neighbor-joining tree verified the classification of all specimens into C. fluminea. Results indicate that the Takahashi River in Kurashiki has been colonized by different morphotypes of invasive C. fluminea since at least 1987.
