Do jellyfish have brains?

No, jellyfish do not have brains. They possess a simple nervous system called a nerve net that allows them to sense light, detect chemicals, and respond to touch. Despite lacking a brain, jellyfish successfully hunt prey, avoid predators, and navigate ocean currents.

How do jellyfish sting?

Jellyfish sting using specialized cells called cnidocytes located on their tentacles. Each cnidocyte contains a nematocyst, a tiny harpoon that fires when triggered by touch or chemicals. The nematocyst injects venom into prey or threats. Thousands can fire simultaneously in milliseconds.

What do jellyfish eat?

Jellyfish are carnivores that eat plankton, fish eggs, small fish, and other jellyfish. They capture prey with their stinging tentacles. Once prey is paralyzed, tentacles pull it to the mouth. Some jellyfish also host symbiotic algae that produce nutrients through photosynthesis.

How long do jellyfish live?

Jellyfish lifespans vary dramatically by species. Some tiny jellyfish live only a few hours or days. Larger species can live several months to a few years. The immortal jellyfish can theoretically live indefinitely by reverting to its polyp stage and restarting its life cycle.

Are all jellyfish dangerous?

No, not all jellyfish are dangerous to humans. Most cause only mild stings resulting in temporary pain and irritation. However, some species like box jellyfish are extremely venomous and can be fatal. The severity depends on the species, sting location, and amount of venom delivered.

How old are jellyfish as a species?

Jellyfish have existed for over 500 million years, making them older than dinosaurs and among the oldest multi organ animals on Earth. Fossil evidence shows jellyfish existed before the Cambrian explosion. Their simple body plan has remained remarkably successful through multiple mass extinctions.

Can jellyfish survive out of water?

No, jellyfish cannot survive out of water for more than a few minutes. Their bodies are 95 to 98 percent water and collapse without the support of surrounding water. They also cannot obtain oxygen outside of water. Stranded jellyfish quickly dry out and die on beaches.

Jellyfish Facts: Types, Lifespan & Ocean Biology

Explore the ancient and fascinating world of jellyfish

Jellyfish have existed for over 500 million years and some species are biologically immortal. Discover jellyfish anatomy, stinging abilities, and lifespans.

Key Facts

Scientific Class

Scyphozoa

Species Count

Over 2,000 species

Age on Earth

500+ million years

Body Composition

95% to 98% water

Size Range

0.04 inches to 6.5 feet wide

Diet

Carnivore (plankton, fish, other jellies)

Swimming Method

Pulsing bell contractions

Nervous System

Nerve net, no brain

Vision

Light sensing organs

Lifespan

Few hours to several years

Reproduction

Sexual and asexual

Habitat

All ocean depths worldwide

Quick Stats

Attribute	Value
Number of Species	Over 2,000 identified
Evolutionary Age	500+ million years
Water Content	95% to 98%
Largest Species	Lion's mane jellyfish
Bell Diameter (largest)	Up to 6.5 feet (2 m)
Tentacle Length (longest)	Up to 120 feet (37 m)
Swimming Speed	Up to 5 mph (8 km/h)
Heart Count	Zero, no heart
Blood	None, absorb oxygen directly

About Jellyfish Facts: Types, Lifespan & Ocean Biology

Jellyfish are ancient marine animals that have existed for over 500 million years, predating dinosaurs and sharks. These gelatinous creatures inhabit every ocean on Earth from surface waters to the deepest trenches.

Anatomy and Physical Structure

Jellyfish have simple but effective body structures consisting primarily of water. Their bodies are 95 to 98 percent water, making them nearly transparent. Jellyfish lack many organs that most animals possess.

Size and Diversity

The smallest jellyfish measure less than 0.04 inches across, barely visible to the naked eye. The largest species, the lion's mane jellyfish, can have bells measuring up to 6.5 feet in diameter. The tentacles of lion's mane jellyfish can extend over 120 feet, longer than a blue whale.

Feeding and Predation

Jellyfish are carnivorous predators that feed on a variety of marine life. Their diet includes plankton, fish eggs, small fish, and even other jellyfish. They capture prey using their tentacles, which trail behind them as they swim.

Movement and Migration

Jellyfish move through water by contracting and relaxing their bell shaped bodies. This pulsing motion pushes water out from under the bell, propelling the jellyfish forward. Most jellyfish drift with ocean currents, though some species can swim actively at speeds up to 5 mph.

Life Cycle and Reproduction

Jellyfish have complex life cycles that include both sexual and asexual reproduction. Adult jellyfish called medusae reproduce sexually. Males release sperm into the water, which females capture to fertilize eggs.

The Immortal Jellyfish

The species Turritopsis dohrnii possesses a remarkable ability that has earned it the nickname immortal jellyfish. When faced with stress, injury, or old age, this jellyfish can revert its cells back to their earliest stage. The mature jellyfish transforms back into a polyp and begins its life cycle again.

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Did You Know?

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Jellyfish have existed for over 500 million years, making them older than dinosaurs and sharks

•

The immortal jellyfish Turritopsis dohrnii can reverse its aging process and theoretically live forever

•

Jellyfish are 95 to 98 percent water and have no brain, heart, blood, or bones

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The lion's mane jellyfish has tentacles that can extend over 120 feet, longer than a blue whale

•

Some jellyfish species are bioluminescent and create natural light shows in the dark ocean depths

•

Box jellyfish are among the most venomous creatures on Earth and can kill a human within minutes

Frequently Asked Questions

One species, Turritopsis dohrnii, can revert to its juvenile polyp stage after reaching maturity, essentially restarting its life cycle. This makes it biologically immortal. However, it can still die from disease or predators. Most other jellyfish species have lifespans ranging from hours to several years.