Jellyfish are fascinating invertebrates—animals without a backbone—that belong to the group Cnidaria.

Their close relatives include corals and anemones, and they come in a dazzling array of shapes, colors, and sizes.

What Do Jellyfish Look Like?

"Jellyfish are gelatinous and jelly-like," explains Miranda Lowe CBE, Principal Curator of Crustacea and Cnidaria.

They feature a bell-shaped body, tentacles hanging down, and a mouth on their underside. Most jellyfish range between two and 40 centimeters in diameter, but some species can exceed two meters, with tentacles extending even further.

Jellyfish Anatomy

Jellyfish have radial symmetry, meaning their body can be split symmetrically like orange segments. Despite lacking bones, brains, hearts, and blood, they possess a nerve net that processes sensory information like light, temperature, and water chemistry.

Jellyfish Species and Classification

Jellyfish belong to Medusozoa, divided into four classes:

Scyphozoa

Around 200 species fall in this category. Most are free-swimming with the signature medusa-shaped body.

Cubozoa

Known as box jellyfish, these 45 species are venomous and excellent swimmers. Chironex fleckeri, the largest, can swim at five centimeters per second.

Hydrozoa

With over 3,600 species, these jellyfish are smaller, and their polyp stage is more noticeable.

Staurozoa

Stalked jellyfish resemble sea anemones and attach to surfaces like rocks and seaweed rather than drifting.

15 Incredible Jellyfish Species

Video by Top Fives

Movement and Diet

How Do Jellyfish Move?

Dear Lykkers. Jellyfish drift with currents but can pulse their bodies to propel themselves weakly. Storms often strand them on beaches in large numbers.

What Do Jellyfish Eat?

Jellyfish use stinging cells to catch prey, directing food into their mouth with oral-arms. Their diet includes small fish, crustaceans, and algae. Larger predators like turtles and sunfish feed on jellyfish, and some species are even considered a delicacy in East Asia.

Fascinating Jellyfish Features

Stinging Ability

Jellyfish tentacles contain nematocytes, which act as tiny harpoons to inject toxins. While stings can cause pain, not all are harmful to humans. Heat rather than ice is often recommended for relief.

Bioluminescence

Some jellyfish can produce their own light, adding to their ethereal beauty.

Immortal Jellyfish

Turritopsis dohrnii can revert to an earlier life stage, effectively making it biologically immortal.

Environmental Impact

Jellyfish Blooms

Blooms, or large gatherings, result from overfishing and nutrient-rich pollution, disrupting ecosystems and machinery.

Climate Change and Pollution

As jellyfish are 95% water, they are sensitive to ocean changes, including microplastic pollution, which enters the food chain through them.

Conservation and Our Role

Reducing single-use plastics and pollution can help sustain jellyfish populations and the ecosystems that depend on them, ensuring their survival for future generations.