Quick answer
Jellyfish are gelatinous marine animals that have drifted through the oceans for over 500 million years, longer than the dinosaurs. They have no brain, heart, or bones, are about 95% water, and capture prey using stinging tentacles. Sizes range from a few millimeters to the lion's mane jellyfish with tentacles over 30 m (100 ft) long, and the box jellyfish is among the most venomous animals on Earth.
Key takeaway
Jellyfish are gelatinous marine animals that have drifted through the oceans for over 500 million years, longer than the dinosaurs. They have no brain, heart, or bones, are about 95% water, and capture prey using stinging tentacles. Sizes range from a few millimeters to the lion's mane jellyfish with tentacles over 30 m (100 ft) long, and the box jellyfish is among the most venomous animals on Earth.
Overview
Jellyfish are gelatinous marine animals that have drifted through the oceans for over 500 million years, longer than the dinosaurs. They have no brain, heart, or bones, are about 95% water, and capture prey using stinging tentacles. Sizes range from a few millimeters to the lion's mane jellyfish with tentacles over 30 m (100 ft) long, and the box jellyfish is among the most venomous animals on Earth.
Biology
Jellyfish (Medusozoa) is classified as Invertebrate with conservation status Least Concern. Typical weight about 2 kg; lifespan around A few months to a few years.
Ecology
Diet: Carnivore (plankton and small fish). Habitat: Oceans worldwide, surface to deep sea. Movement and social systems reflect those pressures.
People and this species
Learn before you travel or keep related pets. Wild individuals are not toys; captive care needs species-specific husbandry.
Further reading
See the full Jellyfish profile for FAQs, taxonomy, and related guides on this site.
Life without a brain
Jellyfish have no brain, heart, blood, or bones. They sense the world through a simple net of nerves and react to light, touch, and chemicals in the water. Made of around 95% water, their bell pulses gently to move, though they mostly drift with the currents.
Stinging tentacles
A jellyfish's trailing tentacles are armed with thousands of microscopic stinging capsules called nematocysts that fire venom-tipped threads on contact, paralyzing plankton and small fish. Some species are harmless to people, while the box jellyfish carries venom potent enough to be life-threatening.
Ancient survivors
Jellyfish are among the oldest animals on the planet, drifting through the seas for more than 500 million years, long before dinosaurs or even trees existed. They survive in every ocean, from warm surface waters to the freezing deep, which is part of why they have endured through mass extinctions.
Blooms and the 'immortal' jelly
Under the right conditions jellyfish can multiply into vast swarms called blooms, sometimes linked to warming seas and overfishing of their predators. One species, Turritopsis dohrnii, can revert to an earlier life stage when stressed, earning it the nickname the 'immortal jellyfish'.
Research notes
Figures for jellyfishs (Medusozoa) come from field studies, museum records, and conservation assessments that do not always agree on exact averages. Prefer ranges over single-point claims, and check whether a source describes wild, captive, or mixed populations.
Practical takeaways
If you encounter jellyfishs in the wild, prioritise distance and local guidance. If you care for related domestic or captive animals, match diet and housing to species needs rather than generic pet advice. Share accurate status information (Least Concern) when discussing conservation.
Sources
FAQs
Jellyfish: Key Facts & Natural History?
Jellyfish are gelatinous marine animals that have drifted through the oceans for over 500 million years, longer than the dinosaurs. They have no brain, heart, or bones, are about 95% water, and capture prey using stinging tentacles. Sizes range from a few millimeters to the lion's mane jellyfish with tentacles over 30 m (100 ft) long, and the box jellyfish is among the most venomous animals on Earth.
What is the scientific name of the jellyfish?
Medusozoa
What do jellyfishs eat?
Carnivore (plankton and small fish)
Where do jellyfishs live?
Oceans worldwide, surface to deep sea
Are jellyfishs endangered?
Listed here as Least Concern. Check IUCN and national lists for the latest assessment.