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Plotiopsis balonnensis (Conrad, 1850)

Diagnostic features

Plotiopsis: Shells moderate to large size; colour - light yellowish brown with flames and speckles. Some spiral, but more prominently widely spaced prominent axial ribs often produced into nodes on the whorl shoulder. The whorls are shouldered. The apical whorls are often corroded. The aperture is oval but with a slightly flaring lip anteriorly; the umbilicus is closed, the columella callus is not greatly thickened or reflected. The operculum is an elongated oval and paucispiral.

Anatomy largely as for the rest of the Thiaridae: The head-foot is short and squarish with a broad bilobed snout. On the edge of the mantle there are numerous finger-like papillae, and long, thin tentacles with eyes at their base. The radula is taenioglossate and typical of thiarids. The ctenidium is long with long filaments. Salivery glands are anterior to the nerve ring. Hyperbranchial gland is weak.  The stomach contains a short style sac, a crystalline style and a gastric shield. The female pallial gonoduct is closed along its entire length. A brood pouch is located in the neck region of the head foot in females.

This species has a large, elongate shell with angulate whorls and strong axial and spiral sculpture. It is usually a light brown colour with dark brown flames and speckles.


Plotiopsis balonnensis (Conrad, 1850)

Common name: Balonne Marsh Snail

Class Gastropoda

Subclass Caenogastropoda

Order Cerithiomorpha

Superfamily Cerithiodea

Family Thiaridae

Genus Plotiopsis Brot, 1874 (Type speciesMelania balonnensis Conrad, 1850)

Original name: Melania balonnensis Conrad, 1850. Conrad, T. A. (1850). Descriptions of new species of freshwater shells. Proceedings of the Academy of Natural Sciences of Philadelphia 5:10-11.

Type locality: Balonne River, Australia (=Balonne River west of Brisbane, Queensland).

Synonyms: Melania lirata Menke, 1843 (junior primary homonym of Melania lirata Benson, 1843) Melania tetrica Conrad, 1850 (non M. tetrica Gould, 1847); Melania oncoides Tenison Woods, 1878; Melania tatei Brazier, 1881 (new name for M. tetrica Conrad); Melania subsimilis Smith, 1882; Plotiopsis centralia Cotton, 1943; Plotiopsis flata Iredale,1944; Plotiopsis subornata Iredale,1943; Plotiopsis thrascia Iredale, 1944; Plotiopsis sociana Iredale, 1944

Biology and ecology

Feeds on detritus, lives in stagnant as well as running waters in rivers, creeks, reservoirs and permanent waterholes in ephemeral rivers. Snails are euviviparous and parthenogenic and only completely developed crawling juveniles (3-7 in most populations and up to 58 in the Finke River populations of Central Australia) with shells comprising several whorls hatch from the brood pouch located in the head.


Throughout mainland Australia with the exception of the Monsoonal Kimberley, Top End and Gulf of Carpentaria areas Endemic to  Australia. In NSW in coastal rivers north of the Shoalhaven River.


The extensive range includes a number of disjunct populations. The species concept employed here requires further testing.

Further reading

Glaubrecht, M., Brinkmann, N. & Pöppe, J. (2009). Diversity and disparity ‘down under’: systematics, biogeography and reproductive modes of the ‘marsupial’ freshwater Thiaridae (Caenogastropoda, Cerithioidea) in Australia. Zoosystematics and Evolution 85: 199-275.

Maaß, N. & Glaubrecht, M. (2012). Comparing the reproductive biology of three “marsupial”, eu-viviparous gastropods (Cerithioidea, Thiaridae) from drainages of Australia’s monsoonal north. Zoosystematics and Evolution 88: 293–315. 

Ponder, W. F., Clark, S. A. & Dallwitz, M. J. (2000). Freshwater and estuarine molluscs: an interactive, illustrated key for New South Wales. Melbourne, CSIRO Publishing.

Smith, B. J. (1992). Non-marine Mollusca. Pp. i-xii, 1-408 in W. W. K. Houston. Zoological Catalogue of Australia, 8. Canberra, Australian Government Publishing Service.

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

Stoddart, J.A. (1983). The accumulation of genetic variation in a parthenogenetic snail. Evolution, 37: 546-554.

Stoddart, J. A. (1985). Analysis of species lineages of some Australian thiarids (Thiaridae, Prosobranchia, Gastropoda) using the evolutionary species concept. Journal of the Malacological Society of Australia 7: 7-16.