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Posticobia Iredale, 1943

Diagnostic features

Shell ovate to broadly conical; sutures slightly to well impressed; body whorl convex to strong­ly keeled, smooth. Operculum flat, paucispiral, yellow, with a white smear and 2–5 (typically 2–3) weakly developed pegs on inner surface. Radula with 3–4 (typically 4) basal cusps on central teeth. Penis simple, tapering; prostate gland closed, more or less kidney-shaped, with pallial vas deferens emerging from just before pallial wall on ventral side. Female genital sys­tem with simple, inverted U-shaped proximal coiled oviduct and short distal coiled oviduct with single bend. Pallial oviduct with opening overlapping anterior end of capsule gland.

Classification

Class Gastropoda

Subclass Caenogastropoda

Order Littorinimorpha 

Superfamily Truncatelloidea

Family Tateidae

Genus Posticobia Iredale, 1943

Type species: Hydrobia brazieri Smith, 1882. Smith, E. A., 1882, On the freshwater shells of Australia. Journal of the Linnaean Society, Zool­ogy 16(92): 255–316.

Type locality: In freshwater creek, Clarence River, New South Wales.

Biology and ecology

Inhabits freshwater springs, streams, rivers, and lakes down to the freshwater-brackish water interface. Found on stones, wood or roots. Can reach very high population densities.  Egg capsules are small (0.3–0.4 mm in diameter) and hemispherical. Eggs are found at­tached to  sand grains, vegetation or, rarely, to the shell of other molluscs.

Distribution

Posticobia is found in a wide range of habitats. from isolated springs in central Australia to the large coastal rivers and lakes of New South Wales, Queensland and Norfolk Island.

Notes

Posticobia is genetically and anatomically closely related to Austropyrgus.

One species, Posticobia norfolkensis (Sykes, 1900), from Norfolk Island is considered possibly extinct.

Further reading

Beesley, P. L., Ross, G. J. B. and Wells, A. (Eds). 1998. Mollusca: The Southern Synthesis. Fauna of Australia. Vol. 5. CSIRO Publishing, Melbourne. Part A. Pp. i-xvi,1-563, Part B i-viii, 565-1234.

Clark, S. A. (2009). The genus Posticobia (Mollusca: Caenogastropoda: Rissooidea: Hydrobiidae SL) from Australia and Norfolk Island. Malacologia 51: 319-341.

Clark, S. A., Miller, A. C. & Ponder, W. F. (2003). Revision of the snail genus Austropyrgus (Gastropoda: Hydrobiidae): a morphostatic radiation of freshwater gastropods in southeastern Australia. Records of the Australian Museum 28: 1–109.

Ponder, W. F. (1981). Posticobia norfolkensis (Sykes), an apparently extinct fresh-water snail from Norfolk Island, Australia (Gastropoda, Hydrobiidae). Proceedings of the Linnean Society of New South Wales 105: 17-21.

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

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. Canberra, A.N.U. Press.