The largest jellyfish is the lion's mane jellyfish (Cyanea capillata). Although most are much smaller, the bell of a lion's mane jellyfish can be over 8 feet across.
As huge as their bell is in diameter, that's not even the biggest part of the lion's mane jellyfish. Their long, slender tentacles can reach over 100 feet, and they have many of them - the lion's mane jellyfish has eight groups of tentacles, and there are 70-150 tentacles in each group. The tentacles hang down underneath the jellyfish's bell, along with its much-folded lips and gonads. All these structures together in a mass resemble a lion's mane.
Interestingly, the lion's mane jellyfish changes in color as it ages. They start out pink and yellow, and then once the bell grows to 5 inches, the jellyfish is reddish to reddish brown. As the bell grows over 18 inches, the jellyfish deepens in color.
Where Are Lion's Mane Jellyfish Found?
Lion's mane jellyfish have a relatively wide distribution - they are found in both the Atlantic and the Pacific Oceans, but in cooler water that is less than 68 degrees F.
What Do Lion's Mane Jellyfish Eat?
Lion's mane jellyfish eat plankton, fish, crustaceans and other jellyfish. They have an interesting feeding strategy in which they rise into the water column, then spread out their tentacles in a wide 'net' and descend, trapping prey as they fall into the water column. This page shows a beautiful image of a lion's mane jellyfish with its tentacles spread out.
Are Lion's Mane Jellyfish Dangerous?
Lion's mane jellyfish stings are rarely fatal, but their stings can be painful, although the pain is generally temporary and causes redness in the area. According to this site, more severe reactions can include muscle cramps, breathing difficulty and skin burning and blistering.
What If I Get Stung?
First, rinse the area with sea water (not fresh water, which can cause more severe stinging), and neutralize the sting using vinegar. Scrape off any remaining stingers using something stiff like a credit card, or by making a paste using sea water and talcum powder or baking soda, and letting it dry. Covering the area with shaving cream or meat tenderizer and letting it dry before scraping it off may also help reduce the sensation and remove stingers.
How to Avoid a Lion's Mane Jellyfish Sting
Lion's mane jellyfish may be large, with a mass of long tentacles, so always give them a wide berth. And remember, the stingers may still work even after the jellyfish has died, so don't assume it's safe to touch a jellyfish, even if it's dead on a beach.