[Hydromedusae] Entirely ectodermal marginal organs sensing orientation and equilibration located in depressions or pockets of the velum. The may remain open (open ectodermal statocysts; e.g., Mitrocomidae, Tiaropsidae) (Open statocyst, Open statocyst 2, Statocyst types); or the velar tissue can seal the sense organ completely (closed ectodermal statocysts; e.g., the other Leptomedusae) (Closed statocyst, Bell margin 2, Statocyst types). Each statocyst contains one or more tiny polygonal or spherical concretions (statolith) (Closed statocyst, Bell margin 2), the closed statocyst having a basal cushion of cells with sensory ciliae (Closed statocyst).