is elongate and broadly oval reaching up to 18 cm in length. The left valve is convex and sculptured with concentric ridges and lines whilst the right valve tends to be flat. There are a few irregular radiating ribs on the left valve which do not normally meet or indent the margin. The shell margin is smooth, and the beaks and umbones are not prominent. The inner surface is pearly white or bluish-white, and the outer surface is deep purple or reddish brown in colour. The adductor muscle scar is near the posterior margin.Similar to Crassostrea gigas
(Thunberg) but lacks the bold ribs and crenulate shell margin typical of Crassostrea gigas
. Both Crepidula fornicata
and Urosalpinx cinera
were introduced with Crassostrea virginica
(Yonge & Thompson, 1976). Crepidula fornicata
out competes the American oyster for space, whereas Urosalpinx cinerea
is a common predator of Crassostrea virginica
. However, if the shell of the oyster is over 0.4 cm thick at the point of attack then Urosalpinx cinerea
will be unsuccessful (Wilbur, 1988).
Crassostrea virginica reproduces externally with both eggs and sperm being discharged through the exhalent siphon. Over 100 million eggs may be liberated from a single female. Spawning of one individual also induces spawning in the surrounding population, therefore maximizing gamete interaction. Interestingly, spawning is temperature dependent; populations in cool temperate waters only spawn at 17°C, while populations in slightly warmer waters spawn at 20°C and sub-tropical populations spawn at 25°C. When transplanted to a different habitat individuals will not spawn, which together with competition and predation pressure from Crepidula fornicata and Urosalpinx cinerea respectivily, are likely explanations for the unsuccessful establishment of Crassostrea virginica.