Large bell
Can reach very large sizes; the largest recorded bell measured about 210 cm in diameter.
Species Guide
What to know about lion’s mane jellyfish
A clean field guide focused on habitat, identification, behavior, and conservation context without burying the useful parts.
The lion's mane jellyfish (Cyanea capillata) 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, and may drift into the southwestern Baltic Sea (where it cannot breed due to low salinity). Similar jellyfish, which may be the same species, are reported near Australia and New Zealand. The largest recorded specimen (measured off Massachusetts in 1865) had a bell diameter of 210 cm and tentacles approximately 36.6 m long. Lion's mane jellyfish have been observed below 42°N latitude in larger bays of the U.S. East Coast.
Occurs in boreal northern seas and may drift into adjacent areas such as the southwestern Baltic Sea; has been observed in larger bays of the U.S. East Coast below 42°N latitude.
Identification
How to identify lion’s mane jellyfish
The visual markers divers can use underwater, plus the species most likely to cause confusion.
Key identification markers
Extremely long tentacles
Recorded tentacle length for the largest specimen was around 36.6 m.
Cold-water distribution
Found in cold, boreal waters of the Arctic and northern Atlantic and Pacific Oceans.
Common lookalikes
Similar southern specimens
Jellyfish reported near Australia and New Zealand are similar and may be the same species.
Range and Movement
How lion’s mane jellyfish move through the world
The broad range, seasonal movement, or migratory behavior that shapes where divers encounter this species.
Occurs in boreal northern seas and may drift into adjacent areas such as the southwestern Baltic Sea; has been observed in larger bays of the U.S. East Coast below 42°N latitude.
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Responsible Encounters
How to dive with lion’s mane jellyfish
Conservation-minded guidance for divers who want the encounter without adding pressure.
Give lion’s mane jellyfish space, avoid blocking the animal's path, and follow local site and operator rules for wildlife interactions with jellyfish.
Field Notes
Interesting things worth knowing
Useful species context that makes the encounter more meaningful once you are underwater.
Field notes
Record size
The largest recorded specimen (1865, off Massachusetts) had a 210 cm bell and around 36.6 m of tentacles.
Breeding limit in Baltic
Individuals may drift into the southwestern Baltic Sea but cannot breed there because of low salinity.
FAQ
Frequently asked questions
Clear planning and conservation answers written for search visibility and AI retrieval.
Research Sources
Lion’s Mane Jellyfish information sources
Primary and credible references behind the field-guide and conservation claims on this page.
Sources 2Last Updated
Lion's mane jellyfish · Encyclopedia · Wikipedia
Primary wildlife guide source.
Cyanea capillata · Taxonomy · WoRMS
Taxonomy reference.
Related Species
More in Jellyfish
Related species guides in the same encounter family.