? Nautilus shell growth

DWhatley

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From @Architeuthoceras I understand that ammonites grew new shell chambers and "moved" forward into the new growth, keeping and closing off the old housing. Somehow I had it in my head that this was true of the nautilus as well because they also have chambers and a siphuncle running through the shell. I have seen different sized nautilus but it did not occur to me until watching @gjbarord 's video (download required, great resolution - S3 in his new publication) that this is definitely not the way the shells grow in the nautilus as they remain the same shape throughout the animals life. I assume that snails do something similar but since they don't shed like a crab how do the shells grow to accommodate the growing animal?
 

Architeuthoceras

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Both Nautilus and ammonoids grow/grew new shell at the aperture, always keeping basically the same shape (different species, different shapes). As the animal grows, they move forward in the living chamber and secrete a new septum at the back of the living chamber just forward of an old septum. There is probably a more pronounced mature modification to the shell of ammonoids, but the overall shape of the shell of both remain the same.
 

DWhatley

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@Architeuthoceras , that is what I always thought BUT I don't see how that can be! If that was true in the nauts, you would see the juvenile shell (as you can in the ammonites) as the animal grows AND the shell would start wrapping around, showing more and more turns. It was the video that got me thinking about this because you can see the juvenile next to the adults and the juvenile shell would not "fit" into the adult configuration at its smallest turns.
 
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D, I'm a little confused as to what you are asking. If you look at a sliced open Nautilus, you can all the chambers, even the juvenile ones. The animal makes the opening wider as it grows.
 

gjbarord

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Hi all,

The external appearance can be a bit deceiving but when sliced down the middle you can clearly see the chambers even formed as a hatchling. As the nautiluses grow, the aperture grows long and wide as the animal ages. And as @Architeuthoceras said, the animal moves forward as they lay new septums. Along those line, @Architeuthoceras have you read anything that suggests whether the movement is "slow" or "fast"? I've seen some strange behavior in captive nautiluses (and also other pictures from another aquarium) that suggests the movement might be fast and might require the nautilus "latching" on to something to physically pull or move forward....

Greg
 
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Greg, I often pondered this myself, on the inside of a Nautilus shell are there marks that suggest that they "creep" forward or is it just one movement forward before they lay down a new septum? How do they hold onto the shell when they let go to add a new septum? Do they have special muscles? I know that I read a paper about this once, it was just too many decades ago to remember the author...

Neale Monks says that Nautilus detach their retractor muscles and then move forward and then reattach, leaving a series of scars on the inside of the shell...

Wow, didn't know we had this link... http://www.tonmo.com/community/pages/morphology/
 
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DWhatley

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I am glad (sort of) that I have not misunderstood the growth and chambering but I still can't see how adding a chamber works and retains the same shape, it is more like the entire shell grows. With ammonites, you can clearly see the shell continue to circle larger and larger but the naut shell retains its new hatch shape through out life and the shell does not circle and appears bigger at the beginning (original end) than it was when it was hatched. Watch Greg's video (requires download) and try to see my brow wrinkle perspective.
 
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Looking for an image to show you what I mean... found this, but not sure it helps...
The chamber is always getting wider as the animal grows so that the older chambers become "engulfed" in the new chamber.

F2.large.jpg
 
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