box jellyfish

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Box Jellyfish Summary

The box jellyfish is a venomous invertebrate that inhabits warm coastal waters around the world. More venomous species tend to live in the Indo-Pacific region and northern Australia, although some species can be found elsewhere. Unlike most jellyfish, they can both swim and see. Scientists attribute dozens of deaths each year to the stings of these often deadly animals. Because of their short lifespan, usually less than a year, they reproduce only once.

deadliest jellyfish box jellyfish
An estimated 50 to 100 people die each year from box jellyfish stings.

©Nuttawut Uttamaharad/

3 Box Jellyfish Facts

  • Most Venomous Sea Animals: These animals are incredibly venomous, especially Chironex fleckeri , Australian box jellyfish, or sea wasps. An estimated 50 to 100 people die each year from box jellyfish stings.
  • Invertebrates: These organisms do not have a backbone. Instead, they have soft, jelly-like bodies and long tentacles. Given that they are invertebrates, they are not actually fish.
  • They can swim: "Real" jellyfish drift with the current rather than propel themselves. The box jellyfish, however, is able to move under its own power, swimming at speeds of up to four knots (4.6 miles per hour).

Classification and Scientific Name of Box Jellyfish

Despite their name, box jellyfish are not fish. Instead, these invertebrates belong to the phylum Cnidaria. Cnidaria include molluscs such as sea anemones, corals, and jellyfish. Scientists divide these animals into four groups: Cubezoans (box jellyfish), Jellyfish (true jellyfish), Anthozoans (true corals, sea anemones, and sea pens), and Hydrozoans (which include hydras, fire corals, siphonophores, and different classes of jellyfish).

The Cubozoa taxon is subdivided into two orders, Chirodropida and Carybdeida. Chirodropida contains three families, while Carybdeida contains five families. In total, Cubozoa contains more than 50 species.

Types of box jellyfish: over 50 different species

There are more than 50 different species of box jellyfish in the world. Here are a few notable examples:

  • Australian box jellyfish or sea wasp (Chironex fleckeri) : This is one of the most venomous animals in the world, with an incredible sting capable of killing its victims within minutes. It is also the largest species in Cubozoa.
  • Irukandji jellyfish (Carukia barnesi) : This species is actually one of several species of Irukandji jellyfish, known for their small size and extreme venom. Its sting can cause Irukandji syndrome, a serious condition whose symptoms include back pain, muscle aches, nausea, sweating, headache, high blood pressure, chest and abdominal pain, and difficulty breathing.
  • South African box jellyfish (Carybdea branchi) : This venomous species inhabits the waters off South Africa.
  • Chiropsoides buitendijki : This species is the only member of the monotype Chiropsoides .
  • Pygmy box jellyfish (Chiropsella saxoni) : Scientists named this species after the 9-year-old boy Saxoni Thomas who discovered it in 2013. Thomas discovered it while playing in a canal on Australia's Gold Coast. The pygmy box jellyfish are less than an inch long, hence the name.
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box jellyfish appearance

10 Most Venomous Animals - Box Jellyfish Photographed in Aquariums
The box jellyfish gets its name from the boxy appearance of its translucent, jelly-like bell.

©Daleen Loest/

They get their name from the boxy appearance of their translucent jelly-like bells. Chung has a mouth and a stomach, but no brain. Clusters of long tentacles protrude from each corner of the bell. These tentacles contain nematocysts, capsule-like structures that release toxic threads and barbs when properly stimulated. The barbs enter the victim's flesh, poisoning them, occasionally causing serious illness or death.

Cubozoans are unique among jellyfish in that they have 24 eyes arranged in clusters of 6. Their four eyes are always pointing towards the sky and are complex structures much like human eyes. These four can make images. The other twenty eyes are simpler and can only distinguish between darkness and light.

Cubozoan species vary widely in size. The smallest species, Irukandji jellyfish (Carukia barnesi), has a bell-shaped diameter of only 0.39 inches. That's in contrast to the largest species, the Australian box jellyfish (Chironex fleckeri) , which has a bell nearly a foot (11.8 inches) in diameter and 9.8-foot-long tentacles. However, even the largest species weighs only 4.4 pounds. Due to their translucent pale blue bodies, these invertebrates are difficult to spot in the water.

Box jellyfish distribution, population and habitat

Box jellyfish inhabit warm coastal waters around the world. This includes parts of the Atlantic, Pacific and Indian Oceans. The deadliest species are usually found in the Indo-Pacific region as well as off the northern coast of Australia. The Gulf of Mexico is another common haunt.

U.S. residents may encounter these invertebrates near states such as Hawaii, Texas, and Florida. They are also common in countries such as Mexico, the Philippines, Malaysia, Thailand, Vietnam, Japan, South Africa, Indonesia, and Australia. They prefer to stay near the surface rather than dive deeper, and they tend to hug the shore rather than swim out into the open ocean. Most species usually do not exceed 184 feet. These factors increase the likelihood of jellyfish-human encounters.

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The box jellyfish is not currently endangered.

The evolution and history of the box jellyfish

Because their soft bodies don't easily fossilize, the evolutionary history of box jellyfish is often difficult to piece together. However, scientists have found potential early cubezoan fossils from the Upper Jurassic (16.35 to 145.5 million years ago), Upper Carboniferous (327 to 299 MYA) and Middle Cambrian (between 541 and 485.4 MYA). Specifically, the fossils of the species Quadrumedusina quadrata and Anthracomedusa turnbulli are from the Upper Jurassic and Upper Carboniferous, respectively.

Significant differences emerged between Atlantic and Indo-Pacific species as cube animals found it difficult or impossible to traverse large expanses of open water. However, one extant genus, Alatina , has evolved to survive in deeper waters near the continental shelf. Certain species in the genus enter shallow water to lay their eggs only a few days after a full moon.

Box Jellyfish Predator and Prey

Box jellyfish are carnivorous and have few natural enemies. Unlike "real" jellyfish, they can chase prey at speeds of up to 4.6 miles per hour. They use the nematocysts on their long tentacles to poison their prey, which they then swallow. Despite this adaptation, they do have some notable predators.

What do box jellyfish eat?

These invertebrates prey primarily on small fish. However, they also eat worms and crustaceans such as shrimp and copepods.

What eats box jellyfish?

The cubic animal's venom successfully deters most predators. However, some marine animals, such as sharks and turtles, will actively target them. This includes green sea turtles, hawksbill sea turtles, and flatback sea turtles. Potential predators also include certain fish such as barreleyes and certain species of crabs.

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turtle breathes through its butt
Certain marine animals, such as sharks and turtles, actively target them. This includes green sea turtles.

© Sullavan

Reproduction and lifespan of box jellyfish

Box jellyfish reproduce sexually and asexually according to their current life cycle stage. As adults in the mature medusa life stage, they move inland from the oceans to rivers, estuaries and marshes to spawn. This happens in spring. Depending on the species, males and females either release their sperm into the water with their eggs, or the male transfers sperm into the female's bell jar to fertilize her eggs. Both males and females die shortly after spawning.

Planulae (larvae) develop outside or inside the female, in which case she releases them into the water. Free-floating plankton end up attaching to objects in the water for safety. Asexual reproduction occurs after the flat body develops into a polyp with multiple tentacles. Polyposis is a form of asexual reproduction in which an organism divides itself into two or more separate organisms. After spending a short time as a baby Medusa, each matures into a fully grown adult.

Cubozoans live up to a year, but their average lifespan is more like eight to nine months. Both males and females reach sexual maturity at two months of age. Due to their short lifespan, they reproduce only once a year.

Box jellyfish in fishing and cooking

Box jellyfish are more often a bycatch than a target for fisheries or sport anglers. This is partly due to their painful and sometimes fatal sting. However, other species of jellyfish are an important part of the economies of some Asian countries, such as China. They can be salted and dried or desalted to reduce the saltiness.

While many species of jellyfish are venomous, in some cases the venom can be removed and the fish meat safely eaten. For example, jellyfish are considered a delicacy in some parts of Asia. It also has many health benefits, including important nutrients, low fat content, and plenty of protein.

While nutritional content varies by species, a cup (58 grams) of dried jellyfish has the following approximate nutritional content: 21 calories, 3 grams of protein and 1 gram of fat.

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