The Lion’s Mane Jellyfish (Cyanea capillata) is the largest known species of jellyfish in the world. It is instantly recognizable by its vibrant coloration, which ranges from light orange in juveniles to deep crimson and purple in larger adults. Its distinctive appearance, characterized by a dense, flowing mass of tentacles beneath the bell, gives the animal its common name, evoking the image of a lion’s mane. The sheer scale it can achieve makes it one of the longest organisms in the ocean.
Maximum Recorded Dimensions
The largest specimen ever documented illustrates the maximum size potential of the Lion’s Mane Jellyfish. This record-breaking individual was discovered washed ashore in 1865 in Massachusetts Bay, United States. Its bell, or main body, had a diameter of approximately 7 feet (2.1 meters).
The trailing tentacles were even more astonishing, measuring about 120 feet (36.6 meters). This length is greater than that of a blue whale, positioning the Lion’s Mane Jellyfish among the longest organisms on the planet. Such extreme dimensions are rare, representing outliers of exceptional growth found typically far offshore in the coldest waters.
Anatomy and Average Size Range
The Lion’s Mane Jellyfish is composed of three main structures: the bell, the oral arms, and the marginal tentacles. The bell is divided into eight distinct, scalloped lobes, giving the animal the appearance of an eight-pointed star when viewed from above. Hanging from the center of the underside are the frilly, highly folded oral arms, which are often about as long as the bell is wide.
The characteristic flowing mane is made up of a staggering number of thin, hair-like marginal tentacles, totaling up to 1,200. These tentacles are grouped into eight distinct clusters, each containing between 70 and 150 individual filaments. Most specimens encountered by coastal observers are significantly smaller than the record holder, typically possessing a bell diameter of 1 to 2 feet (30 to 61 centimeters). The tentacles on these commonly seen individuals usually trail between 6 and 8 feet in length.
Habitat and Environmental Influence on Growth
The ability of the Lion’s Mane Jellyfish to attain large sizes is directly linked to its preference for cold, nutrient-rich environments. This species is predominantly found in the Arctic, North Atlantic, and North Pacific Oceans. The largest individuals develop in far northern latitudes where water temperatures are consistently low, often below 50 degrees Fahrenheit.
Cooler temperatures support seasonal plankton blooms and other prey, providing a massive food supply that fuels rapid growth. The species has an annual life cycle, meaning it hatches, grows, reproduces, and dies within approximately one year. Therefore, the largest individuals must grow from a tiny larval stage to a multi-foot diameter in a single season. Continuous availability of prey is a major factor in their final length, and environmental changes like overfishing can also create favorable conditions for larger occurrences.
Interaction and Sting Severity
While its size and dense curtain of tentacles can appear intimidating, the Lion’s Mane Jellyfish is not considered life-threatening to healthy humans. Its stinging cells, called nematocysts, are used to capture small fish and zooplankton for food. Contact with the tentacles delivers a neurotoxin that causes immediate, painful burning, localized redness, and blistering.
The severity of the reaction depends on the amount of contact and individual sensitivity, but fatalities are extremely rare. A key concern is that the tentacles, which can stretch for dozens of feet, can fragment and still retain their stinging capability. These detached pieces remain biologically active and can deliver a sting even after separating from the bell or washing up on shore. If stung, the recommended first aid is rinsing the area with vinegar and applying heat to help neutralize the venom and alleviate the pain.