CGDP - Shell Microstructure

Different cowrie species thicken their shells with different microstructural layers. All juvenile cowrie grow in the normal prograding spiral fashion as seen in most other snails. This is a three-layer structure comarginal cross-lamellar in between a bottom layer of radial cross-lamellar and a simple surface of prismatic material. At a certain point, the progradation stops (determinate growth), the outer lips turns inward and the shell begins to thicken both internally and externally in sheets of differing arrangement. This is when they get all those great shell features, such as the teeth along the aperture and inhalent and exhalant siphonal canals. In order to expand the list of phylogenetically informative character systems, I've broken a lot of shells to see how each species gets thicker. One outstanding feature of this character system is that it can be tracked through time in the fossil record.

 

 
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FLMNH 2005


 

SEM of juvenile shell - comarginal view
Pris-COMXL-RADXL

Radial view of adult shell (Jenneria) showing
broken COMXL juvenile layer that was fixed
note that the layers are deposited at different times

The entire comarginal cross-section of an adult Cypraea tigris.
The juvenile prograding section is completely surrounded by
surface additions, both above and below. The shift from comarginal
to radial helps to increase the strength of the shell and stop
crack propagation.