E-Fauna BC: Electronic Atlas of the Wildlife of British Columbia

Ceramaster arcticus is small and pentagonal, stiff and firm to the touch, and up to 5.5 cm in greatest radius. It is pale orange with red patches. The ratio of arm to disc is 1.6. The aboral surface has tabulate plates bearing 4 to 12 marginal granules surrounding 1 to 3 smaller central granules. C. arcticus has 18 to 24 massive superomarginals, each usually with a bare spot surrounded by flat granules; the inferomarginals each have a smaller bare spot; papulae cover the aboral surface. The adambulacrals have 2 or 3 short, thick furrow spinelets with 3 to 6 granules on oral surface of the plate, which often has a bivalved pedicellaria.

Ceramaster arcticus differs from C. patagonicus in its smaller average size, fewer granules on the aboral tabulate plates and fewer adambulacral spines.