Hypselodoris decorata has a translucent cream to pinkbody with a broad brown band at the edge of the mantle and four thin opaque white lines on its dorsum. Between these lines are rows of red to purplespots. The anterior end is usually light-purple in colour with white and dark purple spots and the gills have bright red-orange pigment on the apices and outer surfaces. The rhinophores are white, with two red bands on the club and another at the base of the club. This species can reach a total length of at least 25 mm. Previously considered to be a colour variety of Hypselodoris maculosa the distinctive features of this species were elucidated by an integrated molecular and morphological study.