Paul,
Thank you for your response.  Is there a structure in which pushes up the
spines, such as the proboscus or anus of the animal?  Is there a change in
the aragonite crystal microstruture of the spines compared with the rest
of the shell?
Thank you,
Ashley

> Hello Ashley,
>
> Shell spines and other external scupture are secreted by the same organ
> which secretes the rest of the shell, the mantle.  Formation of external
> sculpture occurs at the same place as linear growth of the shell body, at
> the lip of the shell, where new shell material is secreted by the mantle.
> This is true of both gastropods and bivalves. Once a spine, nodule, rib,
> or
> other sculptural structure is created at the lip, shell secretion
> continues
> along the lip, causing the lip to grow out beyond the spine.  Once the lip
> progresses beyond a sculptural structure, that structure does not grow
> further.  If a spine becomes broken after that point, the animal cannot
> repair it because it is beyond the reach of the mantle.  The mantle also
> secretes on the interior of the shell, but that secretion results only in
> increased thickness of the shell body, not linear growth and not external
> sculpture.
>
> In a gastropod, the spiral growth pattern of the shell results in
> sculptural
> elements effectively "rotating" around the shell.  The spines which form
> along the right side of the shell (the lip) at the end of one growth
> period
> will move to the dorsal position during the next period of growth, and
> those
> same spines will further rotate to the left side of the shell during the
> growth period after that.
>
> Paul Monfils
>
>
>
> ----- Original Message -----
> From: "Ashley Spring" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Sunday, December 04, 2005 11:35 AM
> Subject: Spine formation
>
>
>> Conchologists and Malacologists,
>> How are spines formed in mollusc shells?  Is there a body part that
>> pushes
>> the calcite or aragonite up?  Is there a difference in the calcite or
>> aragonite structure of spines compared to the structure of the rest of
>> the
>> shell?
>>
>> I have been searching this subject for a while and there seems to be no
>> literature examining spine formation in molluscs.
>>
>> Thank you,
>> A. Spring
>> PhD student of marine biology
>>
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