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Mitrella australis (Gaskoin, 1852)

Description: Shell broad (for the genus), whorls flat or rounded, spire convex, aperture 40% of shell length. Protoconch of 1 - 1 smooth whorls, large for the genus. Spiral sculpture of cords on base and often a broad, shallow groove below suture; axial sculpture absent. Outer lip sinuous in profile, with shallow sinus; lip thickened externally, thickened internally, with 7-8 denticles. Columella callus sharp-edged, but only in most mature shells, without denticles. Siphonal canal very short. Colour variable; uniformly white, fawn, or orange; or purplish-brown or fawn background, with white spots, axial bands or oblique bands; interior white or mauve. Periostracum with band of axial lamellae below suture.

Size: Up to 20 mm in length.

Distribution: Endemic to Australia; Moreton Bay, Queensland, southwards to Sydney, NSW.

Habitat: Intertidal and subtidal to 80 m. Uncommon.

Comparison: Distinguished from M. semiconvexa by the large protoconch and the lamellate band of periostracum. In shells where these features are lost, some less reliable shell features may be useful: (a) There is often a broad, shallow groove at the position of the lamellate periostracal band (b) Shells are often more elongate than those of M. semiconvexa (c) There is an axial fold behind the outer lip in mature shells; in M. semiconvexa the lip may be smoothly flared but not with an axial fold.

Synonymy: No synonyms.

Remarks: This species is very distinctive when the periostracum and protoconch are intact, but otherwise may be difficult to distinguish from M. semiconvexa. Reports of the species from south of Sydney are probably due to misidentification.

Fig. 1: Balmoral Beach, Middle Harbour, NSW (C.163612)

Fig. 2: North Harbour, Sydney (C.345270)

Fig. 3: Variation

Copyright Des Beechey 2007