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Mitrella tenuis (Gaskoin, 1852)

Description: Shell average width for the genus, spire straight sided, whorls rounded, aperture about 1/3 of shell length; protoconch of 1 smooth whorls. Spiral sculpture of cords on base; axial sculpture absent. Outer lip sinuous in profile, with shallow sinus; lip thickened externally; thickened internally, with 5-8 denticles. Columella callus sharp-edged in mature shells, axial ridge inside edge bearing several denticles. Siphonal canal very short. Colour variable but several predominant patterns; (a) dark brown with white base (b) axial brown flames or spiral band of brown patches (c) white spots in quincunx (d) any combination of these patterns; base usually white. Interior white or fawn. Periostracum smooth.

Size: Up to 16 mm in length.

Distribution: Endemic to Australia; Jervis Bay, NSW, around southern Australia to south-western WA. Also some records of doubtful identification from Sydney.

Habitat: Intertidal on rocky shores.

Comparison: This species is identified by its moderate size, rounded whorls and specific colour patterns. It usually has a white base, but this is a character sometimes seen in other species, particularly M. semiconvexa. It is close to M. semiconvexa but smaller, and many specimens are impossible to positively separate. It is larger than M. leucostoma and of similar shape, and again positive separation is not always possible.

Synonymy: There are three synonyms based on colour forms; Columbella pulla Gaskoin, 1852 is based on a uniformly dark brown shell with white on the columella and the edge of the outer lip (Fig. 2); Columbella saccharata Reeve, 1859 is based on a pink shell with white columella; Columbella nux Reeve, 1859 is based on a "worn and monochrome specimen".

Fig. 1: Victorian coast (C.209737)

Fig. 2:  Huskisson, Jervis bay, NSW (C.163611)

Fig. 3:  Variation

Copyright Des Beechey 2007