The largest of the local jellies, the lion's mane (also called the sea blubber and sea nettle) can reach up to 6 feet in diameter, although it usually is much smaller in Puget Sound.
Produced annually, large individuals can be found from July through September. It can be distinguished from the other large local jelly, the fried-egg jelly, by its vivid, dark-red color and the division of the swimming bell fringe into eight lobes. The thick, frilly material below the bell and inside the reddish tentacles are the oral arms and are extensions of the mouth. Like the tentacles, they contain stinging cells. The tentacles, extended when fishing, can be up to 10 feet long. The animals eat small fish and crustaceans.
Found at the base of the notch between each bell lobe is a sense organ called a rhopalium, a sensor for changes in orientation and light. The lion's mane jelly occurs near shore, at or near the surface, and often is stranded at low tide. Be careful touching a stranded jelly, as the stinging cells may be active even though it appears dead.
The lion's mane sting can be painful. If you are stung, experts recommend that you: 1) Remove tentacles by lifting off rather than scraping; 2) rinse the affected area with sea water, not fresh water; 3) deactivate remaining nematocysts by rinsing with a dilute acid such as vinegar or, in an emergency, human urine; 4) if nematocysts still remain, remove by covering with wet baking power or flour and scraping off with a dull knife; and 5) treat pain with topical anesthetics and see a doctor.
David W. Jamison is a marine biologist and Boston Harbor resident.