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Ascorhis Ponder & Clark, 1988

Diagnostic features

The shell is small, conical and smooth or spirally lirate. The whorls are rounded or angulate, and there is a small umbilicus or chink. The aperture is simple, without a varix and thickening.  Operculum thin, horny, paucispiral, simple. Radula with central teeth having a single pair of basal denticles. Mantle edge lacking pallial tentacle(s), snout with lateral pouches in female used for storing sand grains. Left cephalic tentacle with more pronounced ciliation than right.  Penis with long accessory lobe containing duct of penial gland; penial gland located in basal part of penis. Pallial prostate gland and pallial oviduct open ventrally.

Classification

Class Gastropoda

Subclass Caenogastropoda

Order Littorinimorpha

Superfamily Truncatelloidea

Family Tateidae

Genus Ascorhis Ponder & Clark, 1988

Type species: Bythinia victoriae T. Woods, 1878.

Original reference: Ponder, W. F. & Clark, G. A. (1988). A morphological and electrophoretic examination of Hydrobia buccinoides, a variable brackish-water gastropod from temperate Australia (Mollusca: Hydrobiidae). Australian Journal of Zoology 36: 661-689.

Type locality: Lake Conneware, Victoria.

State of taxonomy

We follow the classification of Ponder and Clark (1988).

Biology and ecology

This tiny species lives on aquatic vegetation in the upper parts of estuaries and in coastal lagoons and is often abundant. It feeds by scraping bacteria and microalgae. The solitary hemispherical, sand-encrusted capsules contain a single egg, and are laided on virtually all substrates including being frequently attached to the shell of Ascorhis and other molluscs that co-occur with it. Development is direct.

Additional information on the biology and ecology of members of this family can be found in Fauna of Australia, vol. 5B, p. 752-755.

Distribution

Gladstone, Queensland, around southern Australia (including Tasmania) and westward to Geraldton, Western Australia.

Notes

This genus is distinguished from all other tateid genera in having open pallial genital ducts, an accessory penial lobe with a penial gland extending to the base of the penis, and

lateral pouches on the snout in females. Ascorhis has a highly variable shell and a number of names occur in the literature. For example, spiral ribs may or may not be present, and the number of ribs and shell size are also variable.

Further reading

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

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.

Ponder, W. F. & Clark, G. A. (1988). A morphological and electrophoretic examination of Hydrobia buccinoides, a variable brackish-water gastropod from temperate Australia (Mollusca: Hydrobiidae). Australian Journal of Zoology 36: 661-689.