Calliotropis ottoi, common name Otto's spiny margarite, is a species of sea snail, a marine gastropod mollusc in the family Eucyclidae.

The thin and delicate shell is rather large for the genus; it is whitish, brilliantly iridescent or pearly, externally and internally.

On the base of the shell there are five or six strong, rounded, revolving ribs, part of them usually somewhat nodulous, separated by deep, concave interspaces, rather wider than he rib; one or two additional ones often appear in the umbilical opening, which is funnel-shaped and moderately large, but often partially obstructed by the reflected (turned outwards) edge of the inner lip.

The interspaces between all the ribs are covered with close, slightly raised lines of growth, and usually with traces of a thin epidermis.

[3] This species occurs in European waters and in the Northwest Atlantic Ocean.