#trochidae

EDIT: ID narrowed down to species - AKA maireener, rainbow kelp shell, or green necklace shell. Endemic to subtidal and the lower intertidal zone off South Australia, Tasmania, Victoria and Western Australia. They've been used for on necklaces by the indigenous women of Tasmania for at least 2,600 years, and probably much longer, but the snail populations have dropped significantly in recent years, to the point that the practise of necklace-making is now threatened.

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Named for their resemblance to Phasianella (pheasant shells) and for being in the Top Shell family, Trochidae.

Seven species, endemic to the coastlines of Southern Australia. The type species was originally Trochus badius, then renamed Catharidus badius, and now Phasianotrochus eximius.

Phasianotrochus are herbivorous mesograzers that feed on kelp, algae, and epiphytes attached to seagrasses.

(source)