Definitions for "Sutures"
narrow wavy lines on the surface of a cephalopod shell, which are lines of junction of septum and the inner side of the phragmocone wall, where each septum contacts the wall of the outer shell. In Nautiloids they are very simple, but in some ammonoids they display astonishing fractal complexity.
In armored species, visible linear boundaries between thecal plates (Steidinger & Tangen 1996).