Morphological Variability of Dreissena polymorpha and Dreissena rostriformis bugensis (Mollusca: Bivalvia)

To date, there are substantially more studies on morphology of D. polymorpha compared to D. r. bugensis (quagga mussel), likely because the geographic range of the latter species has been rather limited until recently. From the period when D. r. bugensis was rst described in 1890 (Andrusov 1890) to the 1940s, this species inhabited a conned area in the lower reaches of the Youzhnyi (South) Bug and the Ingul rivers (Andrusov 1897, Zhuravel 1951). At present, however, the range of D. r. bugensis is almost as large as that of D. polymorpha (Van der Velde and Platvoet 2007, Imo et al. 2010, Benson 2011a,b), which may indicate that its shell morphology may be as variable as D. polymorpha. However, only a few studies describe shell morphology of D. r. bugensis (Andrusov 1897, Zhuravel 1951, Dermott and Munawar 1993, Claxton et al. 1998, Lukashev 1999, Protasov 2004, Hubenov and Trichkova 2007, Van der Velde and Platvoet 2007, Peyer et al. 2010). In the majority of studies, only limited amounts of data on shell form and coloration are given, and no generalizations are provided.