The blue-lined chiton features a head plate adorned with zigzagging white concentric lines, which may appear blue while the creature is alive, and lacks a dark border.

The girdle of this chiton is typically hairless and showcases hues ranging from brown to red or pink, often accompanied by mottling in yellow or white.

[1] Tonicella lineata is very similar but has a dark border to the concentric blue lines on the anterior plate.

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

The natural range of T. undocaerulea stretches from Kodiak, Alaska to Point Conception, California.