Clausinella fasciata is a solid, flat, sub-triangular shell growing up to 2.5 cm long. The outer surface colour is variable, red, pink, purple, yellow or brown but typically with radiating bands and streaks of colour on a paler background. There may be up to 15 broad concentric ridges in older individuals. The margin of the shell may be finely ridged (crenulate). The inner surfaces of the shell are dull white in colour.