Monoplex trigonus, common name the trigonal hairy triton, is a species of predatory sea snail, a marine gastropod mollusk in the family Cymatiidae.

[1] This species is found in the Atlantic Ocean (Cape Verde, West Africa, Gabon, Angola) and in the Caribbean Sea (Venezuela).

[1] The shell size varies between 21 mm and 60 mm.

[citation needed] The maximum recorded shell length is 40 mm.

[2] Minimum recorded depth is 15 m.[2] Maximum recorded depth is 15 m.[2]