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.
Planorbella duryi (Wetherby, 1879)
Common name: Seminole rams horn
Class Gastropoda
Infraclass Heterobranchia
Megaorder Hygrophila
Order Lymnaeida
Superfamily Planorboidea
Family Planorbidae
Subfamily: Planorbinae
Genus Planorbella Haldeman, 1842 (Type species: Planorbis campanulatus Say, 1821, Cayuga Lake, USA).
Original name: Planorbis (Helisoma) duryi Wetherby, 1879. In 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.
On water weeds and other available substrate in ponds, swamps and aquaria in urban areas. Feed on algae and detritus. Egg mass a jelly strip containing small eggs. Development direct.
Introduced from North America to a few scattered localities near urban centres around Australia, most likely from aquaria.
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 Planorbella, P. trivolvis (Say, 1817), is widely distributed in the USA and closely resembles P. duryi but differs in having fine, regular radial riblets.
The figured specimens are possibly P. trivolvis (fide S. Clark).
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Willan, E. C. & Kessner, V. (2021). A conspectus of the freshwater molluscs of the Daly River catchment, Northern Territory. Northern Territory Naturalist 30: 108-137.
