DOI: 10.5061/dryad.dk894
title: Data from: Polarimetry of Pinctada fucata nacre indicates myostracal layer interrupts nacre structure

description: The inner layer of many bivalve and gastropod molluscs consists of
 iridescent nacre, a material that is structured like a brick wall with
 bricks consisting of crystalline aragonite and mortar of organic
 molecules. Myostracal layers formed during shell growth at the point of
 muscle attachment to the shell can be found interspersed within the nacre
 structure. Little has been done to examine the effect the myostracal layer
 has on subsequent nacre structure. Here we present data on the structure
 of the myostracal and nacre layers from a bivalve mollusc, Pinctada
 fucata. Scanning electron microscope imaging shows the myostracal layer
 consists of regular crystalline blocks. The nacre before the layer
 consists of tablets approximately 400 nm thick, while after the myostracal
 layer the tablets are approximately 500 nm thick. A new technique, imaging
 polarimetry, indicates that the aragonite crystals within the nacre
 following the myostracal layer have greater orientation uniformity than
 before the myostracal layer. The results presented here suggest a possible
 interaction between the myostracal layer and subsequent shell growth.
description: Video S1 - polarimetry
 of shell as a function of horizontal positionPolarimetry imaging of
 the Pinctada fucata shell as the shell was moved horizontally through the
 beam, thereby illuminating nacre, myostracal layer, nacre, and prismatic
 layer, in order, shows distinct light transmission patterns for each
 region. The sample was moved horizontally through the beam with the movie
 beginning with imaging the light before it is transmitted through the
 shell, followed by imaging the light as it is transmitted first through
 the nacre, then the myostracal layer, the nacre between the myostracal
 layer and the prismatic layer, and finally the prismatic layer. The
 regions of low intensity within the images are indicative of regions of
 the sample where the transmitted light did not match the selected
 polarization filter, which was held constant throughout the movie. As can
 be seen within the movie, there are repeating fringes of high and low
 intensity with varying periodicity in both nacre
 regions.Video
 S1.movVideo S2 - polarimetry
 of shell as a function of vertical positionPolarimetry imaging of
 the Pinctada fucata shell as a nacre portion of the shell was moved
 vertically through the beam, shows the repetitive nature of the
 polarization fringes within the sample. The sample was moved vertically
 through the beam while the horizontal position was held constant such that
 the beam was transmitted through nacre. The regions of low intensity
 within the images are indicative of regions of the sample where the
 transmitted light did not match the selected polarization filter, which
 was held constant throughout the movie. As can be seen within the movie,
 there are repeating fringes of high and low intensity throughout the
 shell.Video
 S2.movBackscatter scanning
 electron microscope image of the post-myostracal layer
 nacre.Backscatter SEM image
 showing the nacre layers in the post-myostracal layer.6500x BEC 20kV cross-section
 postgrowth nacrescale.tifBackscatter scanning
 electron microscope image of the pre-myostracal layer
 nacre.Backscatter SEM image of
 the pre-myostracal layer nacre highlighting the nacre
 layers.6500x BEC 20kV cross-section
 pregrowth nacrescale.tif