Tonicella lineata is a very colorful chiton, having blue, purple or black straight or zig-zag lines on each of the eight valves.

Mopalia spectabilis looks superficially similar due to its bright blue wavy lines on the valves, but has a hairy girdle.

[1] It can also be confused with Tonicella insignis (Reeve, 1847) which retains the zig-zag pattern in concentric rings on the first and eighth valves and also the lines are most often white.

If knocked from its substrate, T. lineata will contract into a ball in order to protect its vulnerable ventral side, similar to many isopods.

[4] When submerged, gas exchange occurs by water flowing from the anterior portion of the chiton into the mantle cavity where the ctenidia (gills) reside in the pallial grooves.