Mexichromis antonii is a species of sea slug, a dorid nudibranch, a shell-less marine gastropod mollusk in the family Chromodorididae.

[2][3] The holotype of this species was collected in 9 m (30 ft) of water at Punta Aguja (near Mulege), Baja California, Mexico (26°53′N 111°56′W / 26.883°N 111.933°W / 26.883; -111.933).

Three paratypes were also included in the original description, from Isla San Jose, (24°53′N 110°34′W / 24.883°N 110.567°W / 24.883; -110.567), Los Islotes, (24°36′N 110°24′W / 24.600°N 110.400°W / 24.600; -110.400) and Santiago Bay, near Manzanillo, Colima, (19°06′N 104°23′W / 19.100°N 104.383°W / 19.100; -104.383).

[4] Mexichromis antonii has a light blue mantle with two bands of colour at the edge, inner black and outer yellow-orange.

There is a mid-dorsal line of white which is broken into elongate spots surrounded by a pink-magenta region which stretches from the rhinophore bases to the gill.