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Craspedacusta sowerbii (Hydrozoa, Limnomedusae, Olindiidae) is a freshwater jellyfish, which was discovered in England in 1880. Although thought to originate in South America, it became obvious that the species is native to the Yangtze River system in China. It has spread from China into lakes all over the world. Many different species, variations and sub-species have been described based on morphological characters. Specimens discovered in North America were described as separate species, as morphological differences appeared to be significant compared to European specimens. Even within Europe, differences were assumed to be obvious. Up to this point, three valid species are published; others are considered by various scientists to be true species as well, but mostly are recognized as variations. To obtain further insight into population dynamics of C. sowerbii as well as molecular information on the species itself, sequences of internal transcribed spacers (ITS) and cytochrome oxidase subunit I (COI) have been used to analyze specimens collected in Germany and Austria. These sequences have been compared to sequences published of different Chinese Craspedacusta species and variations. In addition, morphological descriptions were compared. For the COI sequences, we found uniformity throughout the complete set of samples. However, no comparisons could be made, as no data had been published on COI of Chinese specimens. ITS1, 5.8S and ITS2, including partial 18S and 28S, sequences, were almost uniform within the German populations, showing only minor base pair exchanges. However, comparisons to Chinese organisms indicated, that the investigated sequences of C. sowerbii from Germany and Austria are similar, although not identical in morphology, to Craspedacusta sowerbii var. kiatingi from China. Overall our data support the assumption that there are three valid species, with the possibility of C. ziguiensis being a fourth one, and several, morphological quite different sub-species or variations of the freshwater jellyfish C. sowerbii.
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