[Crustacea] Small saclike sensory organ, usually containing a granule(s), used to indicate to the animal its orientation; present singly or paired on the pleotelson of some anthurideans.

[Cnidaria] In many hydromedusae, small organs near the margin of the bell which sense posture and detect movement. Each has a small pit, hollow or so-called marginal vesicle. The cavity may be open or closed, this being given significance in classification. Each contains one or more tiny polygonal to spherical concretions (statoliths), often in rows; and closed marginal vesicles may have a basal cushion of sensory cells with hair-like extensions.

Alternative form for statocyst : statocysts.