Trivia merces (Iredale 1924)
Description: Shell elongate, ends rounded, spire usually exposed. Sculptured with strong ribs, about 26 on the outer lip, present on the sides and base but absent on the dorsum. Dorsum smooth. Fossula deep, crossed by ribs. Colour white, with one or several brown blotches on the dorsum, ends pink.
Size: Up to 20 mm in length, commonly about 12 mm.
Distribution: Known from southern Queensland, around southern Australia, to Houtman Abrolhos, WA, including Tasmania. Also northern New Zealand.
Habitat: In NSW, common subtidally under rocks and in crevices, down to about 15 m, and occasionally trawled down to 200 m. In southern Australia it occurs intertidally.
Comparison: T. merces is easily distinguished by its elongate shape and brown spots on the dorsum. T. oryza is more globose, with a deep groove on the dorsum, crossed by weakened or obsolete ribs. T. globosa is smaller, very globular, with a deep dorsal groove not crossed by ribbing.
Synonyms: Trivellona excelsa Iredale 1931 appears to be an unusually large and coarsely ribbed specimen of Trivia merces. (Wilson (1993, p. 210) considered T. excelsa to be a synonym of Trivia producta (Gaskoin 1836), but comparison of the figures of types in Cate (1979) shows that to be unlikely). Iredale also introduced the name Ellatrivia merces addenda Iredale, 1931 for a deep water form which he reported as smaller than the shallow water form, with stronger sculpture on the dorsum. Examination of a range of deep-water specimens was unable to confirm the presence of this form.
Figs. 1,2: Ulladulla, NSW (C.359979)
Copyright Des Beechey 2000