The angularity of this bivalved shell made it immediately noticeable on the sandy beach at Cairns. It is called a Twisted Ark because of the strange configuration of the shell which is strongly twisted with a sharp ridge from the top to the margin. The Latin name is Trisidos tortuosa (Linnaeus), formerly Arca tortuosa. It varies from 60 – 100 mm in length and occurs on the Australian coast from the Northern Territory to Queensland.
Jansen, P. (1996) Common Seashells of Coastal Northern Queensland, privately published in Townsville, Australia, November 1996. ISBN 0 646 29824 0.