Cryptonatica affinis is found in the sandy subtidal, and its shell is globular and the whorls are flattened. The aperture is large and capped by a tight fitting operculum. The Arctic Moonsnail is in the same family (Naticidae) as the Lewis' Moonsnail ( Euspira lewisii). Both are sandy habitat living whelks, and have very similar shell shapes. The Arctic Moonsnail has a more northern and eastern range. It populates the Arctic Ocean and the distribution forks around North America down along the east coast to North Carolina and along the Pacific coast to California. The operculum is thick, white, smooth and calcified with the callus covering the umbilicus; the Lewis' Moonsnail has a brown, uncalcified operculum and an open umbiliucs. Except for the white operculum and callus, the color of the adults Artic Moonsnails is light beige . The size of the adult shell is normally no larger than 25mm high. The juveniles are dark brown with light, irregular stripes and are about the size of a pea.