C. fluminea is a small clam with an inflated shell, slightly round to triangular in shape. The most distinctive feature is the shell which bears numerous heavy concentric ridges. The shell is usually pale brownish or yellowish brown, olivaceous to black. Internally there are three cardinal teeth in each valve and the lateral teeth are heavily serrated. The nacre varies from white to salmon or deep purple. Qiu et al. (2001) reported yellow and brown shell colour morphs amongst specimens collected from Anyue County in Sichuan Province in China. The shells of the yellow morphs were straw yellow on the outside and white on the inside; those of brown morphs were dark brown and purple, respectively. Further analyses revealed that the yellow and brown morphs are triploid and tetraploid, respectively. Both morphs were simultaneous hermaphrodites and brood their larvae in the inner demibranchs. The results indicate that C. fluminea at different ploidy levels is able to reproduce by self-fertilization. The life span is about one to seven years, and it can grow to a shell length of 50-65 mm, although it is usually less than 25 mm.