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.
In addition, the pallial line is a mark on the inner surface of a bivalve shell more or less parallel with the margin caused by the attachment of the mantle .
It has been found that differences in the hinge plate is affected by dentition, while muscle scar is associated with the adductor muscles attaching to it, and the pallial line is attributed to attachment of the mantle into the bivalve shell.
Anatomical Configuration Landmarks 1 Umbo 2 Ventral anterior end of hinge plate 3 Ventral posterior end of hinge plate 4 Dorsal tip of anterior adductor-retractor muscle scar 5 Ventral tip of anterior adductor-retractor muscle scar 6 Anterior end of the pallial line 7 Deepest point of pallial line 8 Posterior end of the pallial line 9 Ventral tip of posterior adductor-retractor muscle scar 10 Dorsal tip of the posterior adductor-retractor scar Table 2: Characters described of the shells of three bivalve species.
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 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.
A similar phenomenon was also revealed in the inner pallial line regions of the exposed A.
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.