It is oval shaped with 8 separate, moderately elevated, overlapping ridged valves on its dorsal surface.

The distribution of Mopalia ciliata is somewhat controversial, however it is agreed that it resides on the southern coast of North America as far south as Baja California.

M. ciliata are found on the underside of rocks near cracks or crevices or other hard stubstrata in intertidal zones.

The valves are strong enough for protection, but shaped so that their bodies are flexible for moving on uneven rocks and turning into crevices.

The mantle cavity is divided into two chambers by ctenidia that circulate water and waste through the chiton.

The gill cilia draw in water through the incurrent chamber and run posteriorly in the excurrent stream where they are discharged.

They have flat and broad setae, which bare found rows of large, curved white calcareous spicules.

Another similarity between these three species is their horizontal canals that flank the jugal area fan out laterally opposed to straight.