Biology/Natural History: _Feeds on coralline algae. Often is found living under the purple urchin Strongylocentrotus purpuratus or in urchin burrows in the rock. This species may home. Predators include Pisaster ochraceous and Leptasterias hexactis, at least in some regions. Eggs are released in April in CA and OR, but in June in the San Juan Islands. Lays a stream of green eggs. Trochophore larva development stops after 150-160 hours, and will not resume unless the larva settles on coralline algae. Larvae metamorphose into juvenile chitons within 12 hours of settling.

Some workers identify the form with pink, blue, and red lines on the plates as T. undocaerulea and identify T. lineata as the form with pinkish valves and dark zigzag lines edged with white.