By far the most common jellyfish species in our waters in the Baltic and North Sea is the moon jellyfish (Aurelia aurita). It appears mainly in summer and early autumn and in some years can be seen in large swarms, known as jellyfish blooms.
The moon jellyfish is characterised by four ring-shaped sex organs in the centre of its transparent bell. They resemble small ears and gave the species its German name. The bell is around 5 to 40 cm across, and the tentacles can range from a few centimetres to about a metre in length.
