The shells were described based on the following characteristics: shell shape, umbo, ligament position, ligament location, ligament type, hinge line, dentition, musculature, pallial line, and pallial sinus.
Results show that the differences are focused on the hinge plate formation, muscle scar position and distance of the pallial line. Differences in the hinge plate are due to dentition.
Based from the results, differences in the hinge plate, pallial line, and muscle scar are found to be significant.
1A-D) from the ventral margin to the pallial line, allowed us to obtain a detailed description from the border toward the inner regions of the shell.
cygnea, from the shell border (Plates 1 and 2, 1.2A-1.20B), through the pallial line (Plate 2, 1.21C), to the interior regions (Plate 2, 1.22C-1.24D).
cygnea was carried out to determine the normal pattern of the microstructure and crystal habit from the ventral margin of the shell to the interior shell surface near the pallial line. From the prismatic (the intermediate) layer, which can be seen in the edge of the shell, it was possible to observe a polygonal arrangement with joined columnar prisms of varying sizes.
In bivalve molluscs, the muscular attachment of the mantle to the shell along the pallial line
further divides the shell-forming compartment into two distinct zones.
In general, the influence of hydrostatic pressure on the calcification mechanisms, on the regions outside and inside the pallial line, resulted in significant alterations of A.
Observations from the shell border to the pallial line showed unconnected nacreous crystals, indicating a greater number of unfinished nacre lamellae that would be expected for normal bivalve nacre.
Columnar layer formation occurs with very particular and strengthened structural alterations of the rhombic crystals on the nacreous region outside the pallial line, resembling intense peaks and troughs.