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Planorbella duryi (Wetherby, 1879)

Diagnostic features

Sinistral, deeply biconcave, shells, whorls strongly keeled at whorl shoulder with a flat spire in juveniles but whorls become more rounded and spire becomes sunken in adults. Umbilicus deep and funnel-like. Animal brown to reddish with a strongly mottled mantle and thin tentacles.

The distinct angle on the top of the whorl (particularly in juveniles) and deeper, overlapping whorls distinguish this species from the similar Planorbarius corneus which is generally flatter and with a more open whorl spiral. The spire whorls are also flatter in Planorbella duryi.

Classification

Planorbella duryi (Wetherby, 1879)

Common name: Seminole Rams Horn

Class Gastropoda

Subclass Heterobranchia

Order Hygrophila

Superfamily Planorboidea

Family Planorbidae

Genus Planorbella Haldeman, 1842 (Type species: Planorbis campanulatus Say, 1821, Cayuga Lake, USA).

Original name: Planorbis (Helisoma) duryi Wetherby, 1879. Wetherby, A. G. 1879. Notes on some new or little known American Limnaeidae. Journal of the Cincinatti Society of Natural History 2: 93-100.

Type locality: Florida, USA.

Biology and ecology

On water weeds etc. in aquaria and small ponds in urban areas. On water weeds etc., in ponds, swamps and aquaria in urban areas. Feed on algae and detritus. Egg mass a jelly strip containing small eggs. Development direct.

Additional information on the biology and ecology of members of this family can be found in Fauna of Australia, vol. 5B, p. 1072-1074.

Distribution

Introduced from North America to a few scattered localities near urban centres around Australia, most likely from aquaria.

Notes

This species is often referred to as Helisomia duryi. It is encountered in the aquarium trade and has established in a few ponds in urban centres around Australia.

Kershaw (1991) suggested this species may be Helisoma anceps. The distinct angle on the top of the whorl (particularly in juveniles) and deeper, overlapping whorls distinguish this species from Planorbarius which is generally flatter and with a more open whorl spiral.

Another species of PlanorbellaP. trivolvis (Say, 1817), is widely distributed in the USA and closely resembles P. duryi but differs in having fine, regular radial riblets. 

Further reading

Baker, F. C. (1945). The molluscan family Planorbidae. Urbana USA, University of Illinois Press.

Beesley, P. L., Ross, G. J. B. & Wells, A., Eds. (1998). Mollusca: The Southern Synthesis. Parts A & B. Melbourne, CSIRO Publishing.

Hubendick, B. (1955). Phylogeny in the Planorbidae. Transactions of the Zoological Society of London 28: 453-542.

Iredale, T. (1943). A basic list of the fresh water Mollusca of Australia. Australian Zoologist 10: 188-230.

Iredale, T. (1944a). Guide to the freshwater shells of New South Wales. Part 2. Australian Naturalist (Sydney) 11: 113–127.

Kershaw, R. C. (1991). Snail and Slug Pests of Tasmania, Queen Victoria Museum and Art Gallery.

Ng, T.H., Tan, S.K., Wong, W.H., Meier, R., Chan, S-Y., Tan, H.H. and Yeo, D.C.J. 2016. Molluscs for Sale: Assessment of Freshwater Gastropods and Bivalves in the Ornamental Pet Trade. PLOS One. DOI:10.1371/journal.pone.0161130.

Shea, M. (1995). Freshwater molluscs of Sydney. Australian Shell News 88: 4-6.

Smith, B. J. and Kershaw, R. C. (1979). Field guide to the non-marine molluscs of south eastern Australia. Australian National University Press, Canberra, Australia.

Smith, B. J. & Kershaw, R. C. (1981). Tasmanian Land and Freshwater Molluscs. Hobart, University of Tasmania.