Jellyfish, gelatinous creatures lacking bones, brains, and hearts, showcase an astonishing variety of shapes, sizes, and colors. Their diversity prompts curiosity about which species holds the title for the largest.
The Reigning Giant
The world’s largest known jellyfish is the Lion’s Mane Jellyfish, scientifically named Cyanea capillata. This species is distinguished by its immense size, particularly in colder waters. The largest recorded specimen was discovered off the coast of Massachusetts in 1865 or 1870, boasting a bell diameter of approximately 7 feet (2.1 meters). Its tentacles stretched an astonishing 120 feet (36.5 meters) long.
The longest tentacles of a Lion’s Mane Jellyfish can exceed the length of a blue whale or even reach the height of a 10-story building. While the record-breaking individual represents an extreme, typical Lion’s Mane Jellyfish can still reach impressive sizes, with bells commonly measuring 1 to 2 feet (30 to 61 centimeters) in diameter and tentacles extending 6 to 8 feet (1.8 to 2.4 meters). These creatures are often described as resembling a “mop hiding under a dinner plate” due to their dense mass of hair-like tentacles. The bell itself is characterized by eight distinct lobes, and from its underside, up to 1,200 tentacles are organized into eight clusters.
Life in the Ocean
The Lion’s Mane Jellyfish primarily inhabits the cold, boreal waters of the Arctic, North Atlantic, and North Pacific Oceans. They are commonly found in regions like the English Channel, the Irish Sea, the North Sea, and western Scandinavian waters. Some have been observed drifting as far south as the Baltic Sea or even near Australia and New Zealand, likely carried by currents.
These jellyfish generally remain near the ocean surface, usually within 66 feet (20 meters) of depth. Their movement relies heavily on ocean currents, as their slow pulsations only weakly propel them forward. Although they are largely solitary creatures, large swarms can occasionally form.
As carnivorous predators, Lion’s Mane Jellyfish feed on a variety of marine life. Their diet includes fish larvae, eggs, small fish, tiny crustaceans, zooplankton, and even other jellyfish, such as moon jellies. They capture prey using their extensive tentacles, which are armed with specialized stinging cells called nematocysts that paralyze their victims. Once immobilized, the tentacles contract and guide the prey toward the jellyfish’s oral arms for consumption.
Beyond the Bell
The life cycle of the Lion’s Mane Jellyfish typically spans about one year. Their reproduction involves both sexual and asexual stages. Fertilized eggs develop into larvae, which then settle on the seabed and transform into polyps. These polyps subsequently bud off into small, free-swimming ephyrae, which mature into the adult medusa form of the jellyfish.
The coloration of the Lion’s Mane Jellyfish can vary, with bells ranging from milky or pale pink to brick red, reddish-purple, or yellowish-brown. Younger individuals often display lighter orange or tan hues, while adults tend to be darker, deepening to red or crimson as they mature. Their tentacles are typically yellow, yellow-brown, or red.
Contact with these creatures can result in a painful sting to humans due to the neurotoxins in their nematocysts. Even detached tentacles or jellyfish washed ashore can still deliver a sting for several days.
Symptoms of a sting usually include localized pain, itching, redness, and a rash. While generally not fatal, severe cases can rarely lead to systemic reactions such as nausea, sweating, muscle cramps, headache, or dizziness. If stung, it is important to carefully remove any remaining tentacles using tweezers or a gloved hand, avoiding direct skin contact. Rinsing the affected area with seawater is recommended, and immersing the sting in hot water (42-45°C or 107-115°F) for 20 to 40 minutes can help alleviate pain. It is important to avoid rubbing the area and to seek medical attention if symptoms are severe or signs of an allergic reaction appear. Vinegar should not be used on Lion’s Mane stings, as it may cause more venom to be released.