Jellyfish are marine invertebrates, found in oceans across the globe. These ancient creatures, lacking brains, bones, and hearts, exhibit a remarkable diversity in size, from nearly microscopic forms to truly immense proportions. Their simple yet effective body plans allow them to thrive in various marine environments. Exploring their size extremes reveals some of the ocean’s largest gelatinous inhabitants.
The Reigning Giant
The largest known jellyfish species is the Lion’s Mane Jellyfish (Cyanea capillata). This creature is named for its dense mass of long, trailing tentacles resembling a lion’s mane. Its bell, or main body, can reach a diameter of up to 7 feet (2.1 meters), and its tentacle length can extend over 120 feet (36.6 meters), rivaling that of a blue whale and comparable to a basketball court. These stinging tentacles are used to capture prey such as plankton, small fish, and other jellyfish. The Lion’s Mane Jellyfish primarily inhabits the cold, boreal waters of the Arctic, North Atlantic, and North Pacific Oceans.
Beyond the Biggest: Other Large Species
While the Lion’s Mane Jellyfish holds the record, other species also achieve substantial dimensions. The Nomura’s Jellyfish (Nemopilema nomurai), found in East Asia, can have a bell up to 6.6 feet (2 meters) in diameter and weigh as much as 440 pounds (200 kg), making it particularly dense. The Giant Phantom Jellyfish (Stygiomedusa gigantea) is an elusive deep-sea inhabitant whose bell can measure over 3 feet (1 meter) across. It possesses four ribbon-like oral arms that can extend more than 33 feet (10 meters) in length, which it uses to envelop prey like plankton and small fish instead of stinging tentacles. It has been observed in oceans worldwide, except the Arctic, typically in the deep-sea’s “midnight zone.”
Why Jellyfish Grow So Large
Several factors contribute to the large size of some jellyfish species. Abundant food sources in their habitats allow for rapid growth. Jellyfish are carnivorous, feeding on zooplankton, small crustaceans, and other jellyfish. Their relatively simple body plan also supports rapid growth. Lacking complex organs and skeletal structures, their gelatinous bodies are primarily composed of water, often over 95%. This high water content allows them to achieve large volumes without requiring a high metabolic rate or extensive energy expenditure for tissue development. In certain environments, the absence of significant predators for large adult jellyfish also allows them to grow unhindered.