This genus is in need of revision, and the species concepts we have used have not been rigorously tested. This situation can only be resolved by additional molecular and morphological studies involving comprehensive sampling.
This rather small, variable species usually has a flat-topped spire and the last whorl is offset from the plane of the other whorls. Sometimes the spire is raised showing sharply stepped whorls as in two of the figured specimens. The periphery is sharply angled, usually with a weak to moderate carina, as in the larger A. carinata, and as in that species, there is usually a weak to moderate concave area just below the carina and the shell surface has weak spiral striae.
Amerianna compar Iredale, 1943
Class Gastropoda
Infraclass Heterobranchia
Megaorder Hygrophila
Order Lymnaeida
Superfamily Planorboidea
Family Planorbidae
Subfamily: Miratestinae
Original name: Amerianna compar Iredale, 1943. In Iredale, T. (1943). A basic list of the freshwater Mollusca of Australia. Australian Zoologist 10: 188-230.
Type locality: Lennard River, north Western Australia.
Synonym: Physa (Ameria) truncata H. Adams, 1861 (non Bourguignat, 1856); Physa (Ameria) obesa H. Adams, 1861, non De Kay, 1843); Amerianna obesula Iredale, 1943, new name for Physa obesa H. Adams..
Note: The type specimen of A. compar is lost but Iredale noted that it was "similar in shape to the Burdekin River shells, but differ in the flattened spire, which shows distinct concentric spiral striae". The reference to the Burdekin River shells relates to Sowerby's (1874) figure of Physa truncata which shows an almost flat spire like the type specimen of Physa carinata figured here. The specimen figured by Sowerby (1874, pl. 3, fig 18) as Physa carinata is a more typical form of A. compar and is figured here.
The species of Amerianna require taxonomic revision - the classification presented here is modified but is based on shells alone.
On water weeds, wood, and similar substrates, in ponds and billabongs. Feeds on algae and detritus. Egg mass a jelly strip containing many small eggs. Development direct.
This species occurs from the Indian Ocean Division, northern Western Australia, across the coastal tropical north of Northern Territory and Queensland, to north-eastern New South Wales.
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 of the Planorbidae. Transactions of the Zoological Society of London 28: 453-542.
Walker, J. C. (1988). Classification of Australian buliniform planorbids (Mollusca: Pulmonata). Records of the Australian Museum 40: 61-89.
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.
