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Ascorhis tasmanica (Martens, 1858)

Description: Shell minute, variable in shape, sculpture and colour. Protoconch of about 1 whorls, nearly smooth, junction with teleoconch sometimes well defined. Teleoconch of up to 3 whorls; whorls rounded, or occasionally angled at periphery. Surface smooth, or with up to 6 spiral threads. Aperture oval, simple, without varix. Umbilicus small or reduced to a chink. Colour translucent pale brown, becoming opaque with age, covered with brown periostracum.

Size: Up to 3 mm in length.

Distribution: Endemic to Australia: Calliope River (north of Gladstone), Qld., southwards and around southern Australia, including Tasmania, to Port Lincoln, SA. The distribution of this species has historically been regarded as extending across southern Australia to south-western WA, but Ponder & Clark (1988) defined the WA population as a new species Ascorhis occidua, based on small differences of the protoconch and the female reproductive system.

Habitat: "This species is found in coastal lagoons, sheltered bays in harbours and inlets, and coastal creeks, and is often locally abundant. Sometimes it lives in impounded water, or in shallow pools, on estuarine flats. It is often found on seagrass ('Zostera') filamentous green algae, or other aquatic plants, or on the submerged parts of emergent plants such as sedges. It is also common on the surface of sediment, stones, dead wood and other surfaces in depths of up to half a metre. It is always submerged." (Ponder & Clark, 1981).

Comparison: This is similar in general form to many other micromolluscs, and is best identified en masse by its habitat and variable sculpture.

Synonymy: This species has long been misidentified in Australian literature as Hydrobia buccinoides, which is a different species entirely. It has been know recently as Ascorhis victoriae (Tenison-Woods, 1878), which is a synonym. There are other synonyms based on various sculptural forms.

Remarks: The anatomy, ecology and distribution of this species is treated in detail by Ponder & Clark (1988).

Fig. 1: Off Eden, NSW (C.315032)

Fig. 2: Baragoot Lake, S of Bermagui, NSW (C.315054)

Fig. 3: Trunketabella Creek, off Tuross Lake, NSW. (C.315064)

Fig. 4: Malabar Creek Lagoon, Moruya River, NSW (C.315058)

 

Copyright Des Beechey 2014