Jellyfish are gelatinous zooplankton of the Phylum Cnidaria. From an anatomical point of view, they are little more than a sac within a sac. Its body composition is 95% water. They have no brain, not even a central nervous system. They lack anything remotely resembling a skeletal system. Most jellyfish don’t even have eyes. Aside from eating, their only interaction with their immediate surroundings is the ability to distinguish between up and down, light from darkness, or physical contact. Yet somehow, their light sensory abilities allow them to perceive and maneuver around foreign objects.

Jellyfish are one of the oldest non-extinct life forms in existence. This should come as a bit of a surprise considering that they are just one rung on the evolutionary ladder of single-celled organisms. Jellyfish fossils have been discovered dating back to the Cambrian period, about 600 million years ago. The Cambrian Period predates not only the extinction of the dinosaurs, but their very existence. These mysterious creatures will likely swim in Earth’s oceans long after humanity is gone.

The largest known jellyfish species is the Arctic lion main jellyfish followed closely by the Nomura jellyfish off the coasts of China and Japan. The largest lion’s mane ever officially documented appeared off the coast of Massachusetts Bay in 1870. Its bell measured 7.5 feet (2.28 meters) in diameter and its tentacles extended to a length of 120 feet (36, 5 meters). There have been claims that larger jellyfish have been discovered since then, but none have been officially documented.

Can you keep a jellyfish in an aquarium?

Most people don’t realize this, but until a few decades ago, scientists didn’t have the technological know-how to keep jellyfish alive in captivity. Jellyfish are 95% water. They would liquefy instantly if sucked into a conventional water filtration system. Jellyfish cannot be housed in a typical square aquarium. They will get stuck in corners and lack the superior brain functioning ability to get out. If there is no turbulent flow in the water, they are reduced to the equivalent of a bowl of gelatin. Keeping a jellyfish in a home aquarium was unthinkable. There was not a single jellyfish display in a public aquarium anywhere in the world.

Jellyfish were first exhibited in a public aquarium just over twenty years ago in Monterey California. This feat was made possible by the pioneering work of the German oceanographer, Dr. Wolf Greve.

Dr. Greve invented a circular aquarium that circulated water in a horizontal circular pattern. He nicknamed his invention the Kreisel tank (carousel in German). This revolutionary aquarium was originally designed for the study of Arctic plankton. The circular design of the tank and the flow of water gently pushed the plankton away from the outer perimeter of the aquarium and into the center of the tank. This technological advance was essential in keeping jellyfish alive in a man-made environment.