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DescriptionTrivia arctica has a small thickly calcified, glossy, egg shaped shell with a length of around 10 mm and width of 8 mm. The upper surface of the shell is reddish-brown while the lower surface is flattened and white. There are no spots on the shell, although the fleshy lobes of the mantle may bear spots. The shell aperture is long and narrow. Closely spaced, thickened ridges run around the width of the shell. When the animal is active the fleshy lobes of the mantle wrap around the shell so that it is almost totally covered. The mantle and the rest of the animal is pale in colour.The shell of Trivia arctica may be confused with that of Trivia monacha, which is slightly larger and has three dark spots down the long axis of the shell. Trivia arctica feeds on ascidians such as Botryllus schlosseri.