Thepallial sinus is an indentation or inward bending in thepallial line on the interior of abivalvemollusk shell's valves that corresponds to the position of thesiphons in those types of clams which have siphons (i.e. siphonate). The position of the pallial sinus is often clearly visible as a shiny line on the inside of thebivalve shell.[1][2][3]
