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Cassidula zonata H. & A. Adams, 1855

Description: Shell thick and solid, aperture more than 50% of total shell length. Spire straight in outline, whorls weakly convex. Shell smooth or with fine spiral grooves and a cord just below suture. Aperture fairly broad, with 3 folds on inner lip, the uppermost undeveloped in immature shells. Outer lip with 1 strong denticle internally, extending as thickening of lip to anterior end. Thick varix outside outer lip. Umbilicus open, with spiral ridge above. Colour brown or greenish brown, with up to 3 white spiral bands, surface covered by thin periostracum.

Size: Up to 10 mm in length.

Distribution: Restricted to eastern Australia: Townsville, Qld, southwards to Jervis Bay, NSW.

Habitat: On mud and under logs among mangroves in upper littoral (Ponder, Clark, Dallwitz 2000). Uncommon.

Comparison: Ophicardelus sulcatus is similar, but does not have a strong denticle inside the outer lip or a varix outside the lip. Pleuroloba quoyi sometimes has similar white bands, but has 2 folds on the inner lip instead of 3, and lacks a varix outside the lip.

Remarks: Excellent photographs of the live animals are given by Denis Riek, at http://www.roboastra.com/Mollusc5/brpr272.html One of these images is reproduced here as Fig. 3.

Figs. 1, 2: 7358-1 7359-1 Carama Creek, Jervis Bay, NSW (C.317087).

Fig. 3: 7360-1 Brunswick River, NSW. Image copyright Denis Riek, 2017.


Copyright Des Beechey 8 June 2018