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817 Views 3 Replies Last post: Jan 24, 2013 1:09 PM by rhossilian RSS
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Jan 24, 2013 9:08 AM

Help with identification of a possible cephalopod

Could you assist in the identification of a marine shell I found recently on a beach on the North Island of New Zealand? This is a modern shell, found alongside large numbers of other shells which had been washed up and deposited on a very gently sloping wide sandy beach. Most of the other shells were marine bivalves, but there were also occasional remains of crab carapaces, and some gastropods. I have attached images of the organism in question.

This fairly thin-shelled organism consits of a single coiled shell of approximately 12-15mm diameter. It is externally quite smooth and lacks ornamentation. The coiling is perfectly planispiral and evolute. The shell is divided into chambers by septa, and the final septum can be clearly seen. It has a septal neck, through which a siphuncle presumably passed. The septal neck is not central, but close to the inner edge of the whorl.

I have ruled out the possibility of it being a nautiloid because of the style of coiling and position of the siphuncle. Also, I believe it not to be a gastropod because of the chambered shell.

Can you assist in this matter? I taught geology for more than 30 years and have not previously encountered a present-day organism such as this. There is a superficial resemblence to an ammonoid, but of course these all died out at the end of the Creataceous Period.

 

Alan C

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