Identifying Nautilus Shells

gjbarord

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Just off of first appearance I would say that they are macromphalus. The key characteristic to look at in regards to nautilus identification is the umbilicus, which is the inner 'coil' of the nautilus at the center of the shell. This is covered in some nautilus and not covered in others.

The striped pattern also appears to be different between those two species. I will double check the ID later today as soon as I can find my reference.

Greg
 

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None of these are N. macromphalus since that species has an open umbilicus and different pattern on the shell. They are probably N. pompilius.
 

robyn

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I'll second that - macromphalus (big bellybutton) has an open spiral - these look to be either pompilius or belauensis, and my understanding is that the major differentiating factor between the two is size - belauensis is typically much larger.

Having said that:

The stripe pattern and size is often totally different within the same species - here's a pic of two pompilius from the philippines and vanuatu: so basically I don't know. I would go with pompilius beacuse its more common than belauensis (IIRC)
 

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Archi

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So, have we concluded a pompilius? I was also wondering if it was different species between the two shells, or if the right one was just a juvenile or different gender.
 

gjbarord

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What is the diameter of the two shells? Is the picture on the right just a little blurry?? (it looked as if there is a slight spiralling to the umbilicus and looks open)

Is the shell smooth or does it feel like a multitude of "cross-grids" along it?

Greg
 

Archi

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Just to correct my last post, I meant the one on the left, the smaller one. Also, here are the measurements. Hope they help!
 

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gjbarord

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The largest reported size for pompilius, I believe, is 17 cm. So I would think that at least the larger one is not pompilius.

What about the cross-grid texture on the shells??

Greg
 

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The largest N. pompilius shell I am aware of measures 268 mm in diameter. 20 cm is pretty big but nothing extraordinary.
 

Archi

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Just remember that I measured from the longest point to the longest point, other specimens may not have been measured that way. As for the texture, there doesn't seem to be any 'cross-grid', rather they have 'bumps' running horizontally (horizontal in the bottom left picture in my first post). It also seems that the smaller one's (the one on the left) 'bumps' are raised quite a bit more than the larger shell (the one on the right).
 

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