Potamopyrgus antipodarum (J. E. Gray, 1853)
Potamopyrgus antipodarum is a small snail, primarily occurring in freshwater, but able to tolerate brackish to near-marine salinities in estuaries (Leclair and Cheng 2011; Hoy et al. 2012). Its overall body shape is conical-oval, with a sharp spire. Its shell is solid, but not thick-walled, and is dextrally coiled, usually with 5-6 and sometimes 7-8 whorls. The aperture is oval, and the inner lip extends completely along the parietal wall. The first whorl is minute and raised, and the subsequent whorls are evenly rounded and separated by a deep suture. The body whorl is bluntly angular. The umbilicus is a narrow slit. The operculum is oval, with the nucleus off-center and a calcium deposit on the inner surface. Specimens in New Zealand may reach 13 mm in shell length, with 7-8 whorls, but a more typical size in introduced populations is 4-6 mm with 5-6 whorls. The color of the shell ranges from light to dark brown. Description from: Winterbourn 1970, Zaranko et al. 1997, New Zealand Mudsnail Management and Control Plan Working Group 2007, and Loo 2012.
All introduced populations are clonal, reproducing parthenogenetically. Individuals can vary considerably in shape, size, color, and shell ornamentation, even within one population, as well as among clones. Some individuals and clones show a sharp, bristly keel on the whorls (Winterbourn 1970; Ponder 1988; New Zealand Mudsnail Management and Control Working Group 2007; Butkus et al. 2012; Loo 2012). At least four clones are known from North America, three from Western North America, and one in the Great Lakes. The clone found in the Great Lakes is also widespread in Europe (Dybdahl and Drown 2011).
West Coast native about 3 mm in size, with a more blunt spire. Found in salt and brackish marshes.
Northwest Pacific native, introduced to brackish marshes in Oregon bays. About 5-6 mm in size, with a blunt spire.
East coast native, about 3 mm in size. Found in salt and brackish marshes.
Freshwater snail, native to Europe, introduced to Great Lakes and East coast rivers. About 12 mm in size, has a more oval shape and a less prominent spire.
East coast native, introduced to brackish waters in San Francisco Bay. Up to 5.5 mm in size, shell is more elongate.