Body elongate, cylindrical, underside of head and body nearly flat; snout blunt; eye high on side of head; mouth small, at lower edge of head, protrusible, top jaw not reaching to under front of eye; relatively small villiform or conical teeth; no teeth on roof of mouth; gill rakers 25-31 (average 28); chin with a pair of large, long barbells, barbel length 17.6-24.5% of SL (average 20.5%); opercle with a spine; 2 well-separated dorsal fins, VIII (first spine minute, often embedded) + I, 8; anal rays I-II, 6; pectoral rays 16 (15-17), fin length 17.9-21.5% of SL (average 20.1%); a forked tail; scales large, slightly rough, 34-38 on lateral line; 6 rows of scales between 2 dorsal fins.
Yellow to greenish yellow on back and top of head, whitish on lower parts; a broad bright yellow midlateral stripe with a thinner bluish stripe immediately above; tail fin bright yellow.
Size: reaches 38 cm.
Inhabits coral and rocky reefs; often seen over adjacent sand and rubble bottoms.
Depth: 2-60 m.
Southern Baja and the Gulf of California to Peru, and all the offshore islands.
Very similar to M. vanicolensis, but differs in having, on average, fewer pectoral fin rays, a slightly shorter pectoral fin, slightly shorter barbels and fewer gill rakers. These differences are so slight that in practice it is probably not possible to separate all individals of the two species when they are together at the same location.