Seashells at Cairns 3.1

Empty shells of Twisted Ark, Trisidos tortuosa (Linnaeus), at Cairns

Seashells at Cairns 3.1 – Twisted Ark, Trisidos tortuosa (Linnaeus), empty marine bivalve shell – inner surface – photographed on the beach at Cairns, Queensland, Australia.

2 Replies to “Seashells at Cairns 3.1”

  1. This is a type of Ark Shell found in north-eastern Australia. It mainly differs from an oyster shell in having a straight hinge line with ‘teeth’ and, when alive, two adductor muscles holding the two valves together. The place where the muscles were attached to the shell are faintly visible as two widely spaced scars on the inside of the shell. On the other hand, shells of the oyster group do not have a straight hinge with interlocking teeth, just a shallow pit that houses a ligament during life. The oyster is also characterised by a single adductor muscle that leaves an almost centrally placed scar on the inside of each valve of the shell.

    I have a particular interest in oyster shells and if you would like to see more articles and pictures about oyster shells on Jessica’s Nature Blog, click here for posts about Oyster Variations or visit my other blog Oysters etc.


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