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Colpospira decoramen (Iredale, 1936)

Description: Shell polished and glossy, protoconch of 1 whorls, teleoconch of 14 whorls in adult shells. Whorls concave in outline, suture incised. Whorls spirally ribbed; latter whorls with two strong spiral ribs at top and bottom, flat or concave between; lower rib frequently doubled on mature specimens; 4-10 riblets in space between ribs, and sometimes several below lower rib. Axial sculpture of growth lines conforming to shape of outer lip sinus. Inner lip flared outwards at lower edge, outer lip thin with deep central sinus, up to twice as deep as wide, but lip usually broken. Body whorl sharply angled, base with numerous concentric riblets. Colour mottled brown and white, forming irregular axial streaks, alternating brown and white on spiral ribs. Operculum circular, corneous.

Size: Up to 30 mm in length.

Distribution: Endemic to Australia; Fraser Island, Queensland, southwards to eastern Victoria.

Habitat: Known from 50-549 meters. Common.

Comparison: This is distinguished from species of similar size by the two strong ribs per whorl, marked with alternating brown and white. Of species of similar size, C. assisa has three strong ribs, without the brown of white markings. C. cordismei also has brown and white bands, but is smaller and has convex whorls.

Remarks: There is considerable variation in the strength of the spiral ribbing. The upper strong rib is almost absent in some shells, and the central riblets may be beaded and approach the major ribs in strength.

Fig. 1: Off Broken Bay, NSW, in 270 m (C.310035).

Copyright Des Beechey 2006