A feather star with ten neatly arranged arms. Each arm being typically 7-10 cm in length. Colouration occurs in patches of red, brown or white. The underside of the arms have an almost smooth exterior. Antedon petasus has 50-100 short banded cirri, generally with 15 segments, which extend from the lower hemispherical plate.Antedon petasus may be confused with the smaller feather star Antedon bifida which has a banded colour pattern of red, pink, orange or yellow and less 30 short cirri on the undersurface of the central disc. Although Antedon petasus is less common than Antedon bifida they are found in similar locations, Antedon petasus being more dominant in northern deep waters.