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Pusillina (Haurakia) discrepans (Tate & May, 1900)

Description: Shell short and wide, spire weakly convex. Protoconch of 1 smooth whorl with distinct junction with teleoconch. Teleoconch up to 4 convex whorls. First teleoconch whorl smooth; axial ribs develop on second whorl, becoming strong by third whorl. Last whorl with axials terminating at narrow spiral cord on periphery; base smooth. Aperture wide, anterior edge formed into broad, shallow excavation, posterior sinus broad; outer lip expanded, with thick varix externally. Shell translucent uncoloured, or fawn, or reddish brown, becoming opaque with age. Protoconch sometimes darker than teleoconch, pink or purple-brown.

Size: Up to 3.1 mm in length.

Distribution: Endemic to Australia: Cape Moreton, Queensland, southwards and around southern Australia, to at least south-western WA, including Tasmania. Two lots from 330 m off Cape Leveque, north-western WA, appear to be the same species.

Habitat: Known from beach washup and down to 183 m. In Sydney Harbour, dredged down to about 20 m. Moderately common.

Comparison: This species stands out in the family by its broad low shape, smooth early spire whorls, and axial ribs that are sharply truncated at the periphery of the last whorl.

Synonymy: Rissoa incompleta Hedley, 1908 is a synonym. Hedley's type figure of this is shown in Fig. 3.

Fig. 1: Cronulla, NSW (C.348234)

Fig. 2: 15 miles off Twofold Bay, NSW, 75-149 m (C.348308)

Fig. 3: Original illustration of Rissoa incompleta from Hedley (1908)


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