I'm sure there is a term for the growth that occurs when the animal forms 2/3 of a new whorl but
essentially they grow very very fast before resting and forming the next shield. It is to say they do not spend a high percentage of their lives between rest phases when they are thickening their shields thus the chances of finding an animal in this phase of its life are not great. The shell is very thin when they are in a growth phase. If the animal dies during a (fast) growth stage it is very likely the very thin new shell will be broken away by the time the empty shell is found. Other mollusks that grow this way such as Charonia, do the same.
I have a friend who found a large Charonia varietgata in the midst of growing new shell section. When he picked up the shell the animal withdrew into its shell breaking the newly formed whorl back to the previous lip from where it had begun its most recent growth. He showed me the shell and there is almost no evidence that the thin section of shell ever existed.
I have found empty Cassis madagascariensis on North Carolina beaches that have the slightest remnants of a very thin whorl larger than what appears to be a complete shell at first glance.

John Timmerman
Wilmington, North Carolina
>
> From: Avril Bourquin <[log in to unmask]>
> Date: 2007/08/26 Sun PM 01:48:19 EDT
> To: [log in to unmask]
> Subject: [CONCH-L] Shell coiling
>
> Hello Conchlers,
>
>
>
> I have been presented with a question that I cannot give a good answer.  It
> comes from Kjell and reads
>
> "Hi!
> A friend and I have been looking at Cassis tuberosa shells and have been
> wondering about how they coil. We never found any specimens that were in
> between finishing one round or the next. They are always at a stage where
> they have already finished a full 2/3s turn. Do you know how that works??
> best wishes from Mexico,
> Kjell"
>
> I will pass on all answers to Kjell.  Thanks in advance for any and all
> help.
>
>
>
> Avril Bourquin
>
>  Invermere, British Columbia
>
> Canada    V0A 1K0
> Email:  [log in to unmask]
>
> URLs:
>
> http://www.manandmollusc.net
>
> http://www.directory.manandmollusc.net/molluscs/
>
>
>
>
>

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