Box jellyfish

The box jellyfish has a body shaped like a box.

It has long, thin strings on its corners. These strings can sting.

Some stings are very painful to people.

These jellies are fast swimmers. They do not just drift in the water. They can swim to hunt small fish.

They have many eyes to help them see. In fact, they have 24 eyes!

These eyes help them move around.

Most box jellyfish live in warm oceans. They like to stay near the shore.

They are very amazing sea creatures.

Box jellyfish have a body shaped like a cube.

They are very different from other jellyfish. Most jellyfish just drift in the water. But box jellyfish are active swimmers. They can swim at speeds of 1.5 meters per second. This helps them hunt for small fish and prawns.

These creatures have a very advanced way of seeing. They have 24 eyes in total. These eyes sit on parts called rhopalia.

Some eyes help them look up at the sky. This helps them find their way home. Other eyes help them avoid hitting things.

Box jellyfish use long tentacles to catch food. These tentacles have tiny tools called nematocysts. These tools act like tiny harpoons. They shoot venom into prey to catch it. Some species have venom that is very dangerous to humans.

Many of these jellies live in warm oceans. You can find them in the Indo-Pacific region.

They often stay near places like coral reefs and mangroves.

Box jellyfish are special living things with a body shaped like a cube.

Most jellyfish just drift with the ocean currents. However, box jellyfish are active swimmers that hunt for food. They can swim as fast as 1.5 to 2 meters per second. This speed helps them chase small fish and prawns. Some species use their long tentacles to catch prey. These tentacles have tiny tools called nematocysts. These act like microscopic harpoons that shoot venom into a victim. While some stings are just painful, others can be very dangerous to humans.

These creatures have a very advanced way of seeing the world. They have 24 eyes in total. These eyes are held in clusters on sensory structures called rhopalia.

Each rhopalium has two lens eyes that form images. One eye looks up to see the sky or tree canopy. This helps species like Tripedalia cystophora find their way home. Another eye helps them see objects so they can swim around them. They also have pit eyes and slit eyes to detect light and movement. A heavy, crystal-like structure called a statolith helps keep their eyes pointed the right way.

Scientists have studied these animals for a long time. For many years, they were grouped with other jellyfish called Scyphozoa. In 1973, experts moved them into their own class called Cubozoa. This change happened because they have a unique way of growing. As of 2018, researchers knew of at least 51 different species. These species belong to different groups, like the order Carybdeida. Recently, in 2023, a new species named Gershwinia thailandensis was found. It was named after the scientist Lisa-ann Gershwin and lives in the Gulf of Thailand.

Box jellyfish live in many warm parts of the world. You can find them in the tropical Indo-Pacific region.

They also live in the Atlantic and east Pacific oceans. Some species live as far north as California and Japan. Others live as far south as South Africa and New Zealand. They like to stay near the shore in places like coral reefs or mangroves. Because they are clear and hard to see, scientists use new tools to find them. One way is using environmental DNA, or eDNA. Scientists collect water and filter it to find tiny bits of genetic material.

Learning about box jellyfish helps us understand how complex life can be. Their nervous system is much more developed than most other jellyfish. They even have a ring nerve to help them pulse their bodies. This allows them to perform fast, fish-like movements in the water. Even very small species, like the tiny Irukandji, can be very powerful. Watching how they hunt and move shows how amazing ocean life is. They remind us that even simple-looking creatures can have very smart ways of living.

Box jellyfish belong to the class Cubozoa. They are invertebrates distinguished by their unique, cube-shaped bodies. Unlike many other jellyfish that simply drift with currents, box jellyfish are active hunters. They can swim at speeds of 1.5 to 2 meters per second. This rapid movement allows them to engage in fish-like behaviors. Some species possess potent venom that can be fatal to humans. For example, species like Chironex fleckeri and Carukia barnesi cause extremely painful stings. Other species, such as Carybdea murrayana, produce painful stings but are not lethal.

The anatomy of a box jellyfish is highly specialized for movement and hunting. The medusa form features a squarish bell. At the rim of this bell is a folded shelf called a velarium. This structure restricts the bell's opening and creates a powerful jet when the jellyfish pulsates. This mechanism enables their impressive swimming speeds. From the four lower corners of the bell, short stalks called pedalia hang down. These stalks hold long, slender, hollow tentacles. In the center of the underside, a mobile appendage called a manubrium hangs near the mouth. The interior of the bell is the gastrovascular cavity. This cavity is divided into a central stomach and four gastric pockets by four equidistant septa.

Box jellyfish possess a sophisticated sensory system. They have a ring nerve at the base of the bell to coordinate pulsing. They are unique among jellyfish for having true eyes with retinas, corneas, and lenses. These eyes are located on sensory structures called rhopalia. Each of the four rhopalia contains six eyes, totaling 24 eyes. Each rhopalium has two image-forming lens eyes. One lens eye looks upward to help with navigation, such as observing tree canopies in mangrove lagoons. The other lens eye helps the animal avoid obstacles. They also have pit eyes for light detection and slit eyes to sense vertical movement. A heavy, crystal-like structure called a statolith keeps the eyes oriented vertically.

Taxonomy and the history of discovery have evolved as scientists learned more. Historically, cubozoans were classified as an order of Scyphozoa. However, in 1973, they were moved into their own class. This change was due to their unique morphology and a biological cycle that lacks strobilation. As of 2018, at least 51 species were known. These are organized into two orders and eight families. In 2023, a new species named Gershwinia thailandensis was discovered in the Gulf of Thailand. It was named after scientist Lisa-ann Gershwin. This species is unique because it has specialized horns and lacks a common digestive system.

These animals are widely distributed across tropical and subtropical oceans. They live between 42° N and 42° S latitude. While many dangerous species stay in the Indo-Pacific, others inhabit the Atlantic and east Pacific. Species have been found as far north as California and Japan. They also live as far south as South Africa and New Zealand. They often reside near shores in habitats like coral reefs, mangroves, and kelp forests. Because they are translucent, they are difficult to detect. Scientists now use environmental DNA, or eDNA, to find them. This method involves filtering water through a cellulose nitrate membrane to find genetic material.

The life cycle and hunting methods of the box jellyfish are quite complex. To hunt, they extend their tentacles and swim upward. Then, they turn upside-down and stop pulsating to sink slowly. Prey, such as small fish or prawns, becomes entangled in the tentacles. Each tentacle can have about 15 tentacles per corner and contains 500,000 cnidocytes. These cells hold nematocysts, which are microscopic, harpoon-shaped mechanisms that inject venom. Researchers use statoliths, made of calcium sulfate hemihydrate, to study their age. These structures grow in daily layers. For example, Chironex fleckeri can reach an inter-pedalia distance of 100 mm by 45 to 50 days old.

Reproduction in Cubozoa also shows fascinating variety. Most species follow an annual life cycle and reach maturity when their bell is 5 mm wide. The order Chirodropida uses external fertilization. In contrast, the order Carybdeida uses internal fertilization. Some species, like Carybdea sivickisi, even perform a "wedding dance" to transfer sperm. While it was once believed they were semelparous—meaning they reproduce only once before dying—new research suggests otherwise. The species Chiropsalmus quadrumanus may be iteroparous, meaning it can reproduce multiple times. This discovery changes how we understand the life history of these incredible marine invertebrates.