Diagram of the internal shell structure of the left valve of bivalve resembling a venerid in which the pallial line is shown
The pallial line is a mark (a line) on the interior of each valve of the shell of a bivalvemollusk. This line shows where all of the mantle muscles were attached in life. In clams with two adductor muscles the pallial line usually joins the marks known as adductor muscle scars, which are where the adductor muscles attach.
The position of the pallial line is often quite clearly visible as a shiny line on the slightly more dull interior surface of the bivalve shell.
^Huber, Markus (2010). Compendium of Bivalves. A Full-color Guide to 3'300 of the World's Marine Bivalves. A Status on Bivalvia after 250 Years of Research. Hackenheim: ConchBooks. pp. 901 pp. + CD. ISBN 978-3-939767-28-2, at p. 57