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Glacidorbis Iredale, 1943

Diagnostic features

Shell small to minute, dextral, orthostrophic, near planispiral with wide, shallow umbilicus. Protoconch terminated by abrupt change in sculpture, lacking varix; sculptured with pustules or pits over whole surface, or on initial portion only with remaining part smooth. Teleoconch whorls evenly convex or ridged or keeled near mid-dorsally and near mid ventrally, sculptured with orthocline axial growth lines or ridges, sometimes also with spiral sculpture. Operculum circular to oval, multispiral to paucispiral, with central, subcentral to eccentric nucleus, and surface covered with minute pustules.

Headfoot with long cephalic tentacles, the snout is short and very broad and fused to the dorsal part of the anterior foot, the eyes are in the middle of the tentacle bases. Foot posteriorly bifid, anteriorly with lateral processes. Jaw with dorsal and ventral elements. Radula with large central teeth bearing several sharp cusps on a pointed mesocone, with broader, arched base lacking additional cusps. Lateral teeth vestigial or narrow and small; marginal teeth absent. Mantle cavity widely open, not modified as a lung, with ciliated ridge on right side. The kidney is in the mantle roof, an there is no gill.

Protandrous, and several large embryos brooded in mantle cavity. Penis narrow and small, completely invaginated, with large sucker or knob-like glands in the large praeputium.

Classification

Class Gastropoda

Subclass Heterobranchia

Superfamily Glacidorboidea

Family Glacidorbidae

Genus Glacidorbis Iredale, 1943

Type species: Glacidorbis hedleyi Iredale, 1943

Original reference: Iredale, T. (1943). A basic list of the freshwater Mollusca of Australia. Australian Zoologist 10(2): 188–230.

Type locality: Blue Lake, Mount Kosciusko, NSW, 36°24'S, 148°19'E, dredged from 35 ft (10.7 m).

State of taxonomy

We follow Ponder and Avern (2000) in this resource.

Biology and ecology

Glacidorbis species are carnivorous feeding on living and dead invertebrates. Glacidorbis species inhabit swamps, bogs, streams and rivers where they are normally found on macrophytes, moss, roots, pieces of wood, or under stones (rarely). Glacidorbis occidentalis and G. hedleyi can occur in ephemeral habitats whereas most other species live in permanent to semi-permanent streams or swamps. Glacidorbis hedleyi and Glacidorbis occidentalis are oviparous and display brooding of the young within the pallial cavity. Glacidorbis occidentalis young develop into mature females. Veligers are present soon after adults emerge. Small snails appear during late winter to early spring, reaching adult size by summer. Glacidorbis hedleyi is the only species known so far to have the unusual reproductive mode where protandric males must copulate before turning into females.

Distribution

South-eastern and south-western Australia from northern New South Wales to Tasmania, Victoria and southeast South Australia, with a disjunct population in the south west corner of Western Australia.

Further reading

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

Meier-Brook, C. & Smith, B. J. (1976). Glacidorbis Iredale 1943, a genus of freshwater prosobranchs with a Tasmanian-Southeast Australian-South Andean distribution. Archiv Für Molluskenkunde 106: 191-198.

Ponder, W. F. (1986b). Glacidorbidae (Glacidorbacea: Basommatophora), a new family and superfamily of operculate freshwater gastropods. Zoological Journal of the Linnean Society 87: 53-83.

Ponder, W. F. & Avern, G. J. (2000). The Glacidorbidae (Mollusca: Gastropoda: Heterobranchia) of Australia. Records of the Australian Museum 52: 307-353.

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

Smith, B. J. & Kershaw, R. C. (1981). Tasmanian Land and Freshwater Molluscs. Hobart, University of Tasmania.

Rumi, A., Gutiérrez Gregoric, D. E., Landoni, N., Cárdenas Mancilla, J., Gordillo, S., Gonzalez, J., & Alvarez, D. (2015). Glacidorbidae (Gastropoda: Heterobranchia) in South America: revision and description of a new genus and three new species from Patagonia. Molluscan Research 35: 143-152.