Blue Jelly

Blue jellyfish age can be identified by colour of their bell. They tend to be pale in appearance when young, but mature to have a brightly purple-blue (some yellow) coloured bell. Although it is similar to the lion's mane jellyfish, the blue jellyfish is not as large, and has a translucent bell.

C. lamarckii has a blue or yellow tone and grows to approximately 10 to 20 cm (4 to 8 in) across the bell, but specimens can grow to 30 cm (12 in). In Scandinavian seas, this species rarely grows larger than 15 cm (6 in).

This species is found in the pelagic zone off the west coast of Scotland, the North Sea, the English Channel, and the Irish Sea, sometimes with the more common lion's mane jellyfish (Cyanea capillata). It is also found in the Kattegat along the Swedish western coast as well as in Danish waters.

The medusae bud and loosen from the mature polyps between January and March around the British Isles and southern North Sea. This occurs in a similar way to the life cycle of the moon jellyfish. These blue jellyfish live for less than a year.