This species is distinguished from its congeners, except planquettei, zorroi, by having its anteriormost spine of prepelvic serra reaching only the middle of the abdomen between the verticals through pectoral and pelvic-fin origins (vs. reaching the vertical through pectoral-fin origin or almost so); differs from asterias, lobatus, planquettei, rhomboidalis, rubripinnis, ternetzi, zorroi by having fewer scale rows between lateral line and dorsal-fin origin 30-35 (vs. 36-61), and between lateral line and pelvic-fin origin 27-31 (vs. 32-63); from asterias, levis, tiete, torquatus, by having 18-22 branched dorsal-fin rays (vs. 24-27); from M. arnoldi by having a relatively elongate body, its body depth 53.0-64.5% of SL (vs. 69.0-76.9% of SL); from M. ternetzi by the presence of a pair of symphyseal teeth on dentary (vs. none); from M. schomburgkii by the absence of a vertical black stripe on middle portion of flank (vs. presence) (Ref. 114774).