Small chitons, 20-25 m; with strongly pustulose radial ribs. Setae very long, up to one half of animal length, bearing usually strongly recurved, ringlet like bristles. Habitat. Lives on the sides and bottoms of cobbles & boulders in relatively calm areas with good current or tidal exchange, and on rock walls, from the low intertidal (Hanselman, 1990) to at least 40 m.
Distribution. Found from Unalaska Island, Aleutian Islands, Alaska to San Mateo County, California.
Occurrence. Rare to uncommon.
Comments. This species may be distinguished from the similar M. sinuata by 1) the strongly pustulose sculpture of the radial ribs, and 2) the very long setae, up to Vi of the animals length, bearing a single row of long, usually ringlet-like bristles.