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Amphithalamus jacksoni (Brazier, 1895)


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Description: Shell minute, solid, spire convex in outline. Protoconch paucispiral, rounded, with spiral rows of minute pits, with weak varix forming distinct junction with teleoconch. Teleoconch whorls weakly rounded, sometimes with faint spiral threads on upper quarter of whorls; no axial sculpture Aperture ovate, with no anterior or posterior canals. Inner lip of aperture separated from previous whorl by deep channel, with a callus plug at suture. Outer lip without varix externally, smooth internally. Umbilicus closed. Colour fawn.

Size: Up to 2.0 mm in length.

Distribution: Endemic to Australia: Bowen, Queensland, southwards to Twofold Bay, NSW.

Habitat: Empty shells are uncommon in beach washup. Living specimens and empty shells are moderately common in dredgings, down to 118 m. 

Comparison: See A. incidatus.

Synonymy: This species was first described as Rissoa badia Watson, 1886, but that name was preoccupied, and was replaced by Brazier's name.

Remarks: There is some intraspecific variation in spire shape, from moderately convex (Fig. 1) to almost pupoid. In very mature specimens the final section of the last whorl becomes a little detached from the parietal wall, as in the genus Badepigrus.

Fig. 1: Sow and Pigs Reef, Port Jackson, NSW (C.65202)


Copyright Des Beechey 2010, modified 2014