Examination of statocysts of scyphomedusae and cubomedusae to clarify phylogenetic relationships and to develop a method for the age determination of medusae

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Disc-shaped jellyfish (Scyphozoa) and box jellyfish (Cubozoa) have complex sense organs (rhopalia), which contain anorganic crystals (statoliths). The chemical composition, the crystallography and the morphology of these crystals in some species have been examined and some differences between the distinct taxa were shown in several publications with participation of the applicant, Dr. Ilka Sötje. Continuing examinations shall contribute to the identification of taxonomical relationships of jellyfish, for example the disputed relationships within the root-mouth jellyfish (Rhizostomeae), which have yet to be clarified with molecular methods. The statoliths of the box jellyfish and the disc-shaped jellyfish shall be examined in comparison. To date, they have been grouped into two different taxa (classes), but are presumably more closely-related to each other than is presently assumed. Statoliths of full-grown animals of both taxa have a very different morphology, but recent investigations have shown similarities regarding the statolith morphology in young specimens of both groups; this shall be examined in detail in the context of this application.The detailed analysis of statoliths in medusae of different age groups shall lead to the development of an age-determination method for jellyfish. The gelatinous body of jellyfish is shrinking and growing depending on environmental conditions. Therefore, most body parts of the medusa cannot be used for age determination, but changes in the number and size of the statoliths during medusa development can be used for age-determination. The determination of age is the basis for studies of population dynamics and is crucial for the elucidation of the reasons for the observed worldwide increase in mass occurrences of jellyfish.