The Cyaneidae are a family of true jellyfish. About 20 species are in this family, including the well-known lion's-mane jellyfish.

Cyaneidae. Retrieved May, 22 2023, from en.wikipedia.org/wiki/Cyaneidae.

The lion's mane jellyfish (Cyanea capillata), also known as the giant jellyfish, arctic red jellyfish, or the hair jelly, is one of the largest known species of jellyfish. Its range is confined to cold, boreal waters of the Arctic, northern Atlantic, and northern Pacific Oceans. It is common in the English Channel, Irish Sea, North Sea, and in western Scandinavian waters south to Kattegat and Øresund. It may also drift into the southwestern part of the Baltic Sea (where it cannot breed due to the low salinity). Similar jellyfish – which may be the same species – are known to inhabit seas near Australia and New Zealand. The largest recorded specimen was measured off the coast of Massachusetts in 1865 and had a bell with a diameter of 210 centimetres (7 feet) and tentacles around 36. 6 m (120 ft) long. Lion's mane jellyfish have been observed below 42°N latitude for some time in the larger bays of the East Coast of the United States.

Cyanea capillata. Retrieved May, 22 2023, from en.wikipedia.org/wiki/Lion%27s_mane_jellyfish.