Statocysts and Statoliths

Statocysts, the balance organs of jellyfish, are located at the bell rim of the medusae. They contain tiny crystals, the statoliths, representing the only solid and inorganic structures in the gelatinous medusa bell. Statoliths are composed of calcium sulfate hemihydrate (basanite), a substance with an extremely hygroscopic nature leading to difficulties in investigations on statoliths.

Our studies on scyphozoan and cubozoan statoliths and statocysts in collaboration with the University of Hamburg (Dr. Ilka Sötje), funded by the German Research foundation (DFG), provide new insights into the scientific potential of these structures (Holst et al. 2016, Sötje et al. 2017, Heins et al. 2017). We used a combination of methods, modified for the particular requirements of statoliths: light microscopic studies with a slide scanner, application of the fluorescent marker calcein on statoliths combined with confocal laser scanning microscopy (cLSM), 3D-reconstructions from X-ray micro-tomographic data (µCT), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and Single-Crystal Analysis.

The size, growth, and number of scyphozoan statoliths increase with increasing medusa size, indicating the potential of these crystals for medusa age determination. Moreover, investigations on scyphozoan statocysts indicate taxon-specific differences in the morphology of the statolith arrangement and in statolith shapes.