Phyllidia monacha Yonow, 1986 Phyllidia monacha is a species of sea slug, a dorid nudibranch, a shell-less marine gastropod mollusk in the family Phyllidiidae.

[2] This species was described from Creek, Jeddah, Red Sea 21°44′N 39°07′E / 21.733°N 39.117°E / 21.733; 39.117.

[3] This nudibranch has a white dorsum with a pattern of black and orange.

The black pigment forms an irregular ring around the middle of the back with radiating lines extending to the mantle edge.

The centre of the back and the edges of the mantle between the black markings have patches of orange-yellow.