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Hypermastus mucronatus (G.B. Sowerby II, 1886)

Description: Shell large, protoconch very small. Early teleoconch whorls rapidly expanding, then spire straight or weakly convex in profile; spire occasionally slightly bent. Whorls flat or weakly convex, suture well defined. Scars from outer lip positions faint, infrequent. Aperture short, about one-quarter of shell length; outer lip expanded, almost straight or weakly sinuous in profile. Shell glossy, colourless transparent.

Size: Up to 12 mm in length.

Distribution: Literature reports from NSW, Vic., Tas, SA and south-western WA. Specimens seen from Sydney Harbour, beach and 11-16 m.

Habitat: Species of Hypermastus are parasitic on sand dollars (Warén, 1984), but there have been no observations specifically on the host of this species. Uncommon.

Comparison: This species reaches more than twice the size of H. coxi. Small specimens resemble H. coxi in shape, but may be recognized as immature by lacking a thickened, expanded outer lip to the aperture.

Remarks: Laseron (1955) inadvertently interchanged the identification of H. muctronatus and H. coxi. His figures in Plate 1, figs. 6-8 labelled as H. coxi are actually H. mucronatus.

Fig. 1: Sow and Pigs Reef, Sydney Harbor (C.111515)


Copyright Des Beechey 2015