C. fleckeri, commonly known as the Sea Wasp, is the most dangerous jellyfish and considered to be one of the most dangerous creatures in the world. This species is pale blue in color, posing a danger to swimmers since its transparency makes it difficult to see in the water.

"Chironex fleckeri is one of the simplest organisms. The bi-radially symmetrical body has well developed tissues and specialized cells. The outer covering of ectoderm made of milky slime substance and an inner layer of endoderm makes it displobastic. It has an organic exoskeleton and hydrostatic skeleton and it is an encephalized organism with a non-cellular mesoglea separating the two layers and spreading to a vast bulk of its body which aids its buoyancy. With only a single opening (the mouth and entrance to the cavity), the body encompasses a single sac-like body space called the Gastro-vascular ..It is called the box jellyfish because its transverse section appears to be squared-umbrella -shape with its tentacles at the corners of the box margin. The edge of the umbrella turns inwards forming a circular shaped structure called Velarium. It possesses four dark spots (primitive eyes) that are sensitive to light. These enable it to avoid colluding with foreign objects, detection of foods, and orientation for swimming. It has a simple but well-developed and sophisticated nervous and sensory systems but no specialized excretory respiratory and circulatory organs since most of its living cells are in direct contact with the water." (McEldowney)

Chironex fleckeri, also known as box jellyfish, lives in and around the waters of Australia and Southeast Asia. They inhabit parts of the Indian Ocean, Pacific Ocean, and the Great Barrier Reef. Box jellyfish have been found in the waters on the western coast of Australia in the Exmouth Gulf to Gladstone in the northern waters of Australia. Humans are frequently stung by this species in the oceanic waters of Queensland, on Australia's eastern coast. Box jellyfish may also be responsible for stings near the Philippines.

Biogeographic Regions: australian (Native ); indian ocean (Native ); pacific ocean (Native )

Found in the coastal areas of Northern Australia, Africa, the Gulf of Mexico (near Texas), South-Eastern Asia, and adjacent areas of the tropical Indo-west Pacific.

The name box jellyfish is derived from the shape of their bell, which is box-shaped when healthy. The bell is transparent and is usually between 16 and 24 cm, though some reach a diameter of 35 cm. The tentacles of box jellyfish dangle from pedalia, the corners of the bell. There can be as many as 15 tentacles hanging from each of the four pedalia for a total of up to 60 tentacles per jellyfish. Each of the tentacles has a slight blue-gray tint and can grow up 3 m in length. Each tentacle contains millions of nematocysts, which are microscopic hooks where venom is held and delivered. Box jellyfish contain sensory organs including 24 eyes, but they do not have a brain.

Range mass: 2 (high) kg.

Range length: 3 (high) m.

Other Physical Features: radial symmetry ; venomous

Square in shape, they can grow to be as big as a baseball. Their 60 tentacles are each approximately 15 feet long

Box jellyfish tend to inhabit shallow, murky saline waters near Australia. They are mainly found in the ocean but are also found inland in freshwater rivers and mangrove channels during spawning. During heavy storms, they move into deeper waters where the water is calm to avoid damage. Box jellyfish also inhabit shallow rivers during the reproductive season and during their polyp stage. Once young jellyfish mature into medusa, they follow the river out to sea.

Habitat Regions: saltwater or marine

Aquatic Biomes: reef ; rivers and streams; coastal

Adult box jellyfish tend to feed in shallow waters, mainly on small fish and prawns. Until they are fully grown, box jellyfish feed primarily on shrimp, most commonly Acetes australis. Box jellyfish rely on their venomous tentacles to capture their prey. The millions of nematocysts on their tentacles enable box jellies to deliver lethal does of venom to their prey, immobilizing or killing them in a short amount of time. Because each nematocyst is so small and releases only a minute amount of venom, box jellyfish discharge as many of its nematocysts as possible. Once the tentacles capture the prey, box jellyfish bring it in closer to their bell and other tentacles, allowing use of nematocysts from other tentacles to more quickly immobilize and kill the prey.

Animal Foods: fish; aquatic crustaceans

Primary Diet: carnivore (Eats non-insect arthropods)

Box jellyfish prey on prawns, shrimp, and small fish, though box jellyfish do not greatly affect populations of these species. Green turtles (Chelonia mydas) prey upon box jellyfish, but jellyfish are not their primary source of food.

Box jellyfish have few known predators because of the stinging cells (nematocysts) on their tentacles. These nematocysts are extremely venomous to most species. The only known predator of box jellyfish are green turtles. Venom does not penetrate the thick skin of green turtles, which are thus unaffected by the stings of box jellyfish.

Known Predators:

• Green turtles Chelonia mydas

Because box jellyfish have no brain, it is difficult to define their communication and perception. Box jellyfish do have eyes, which have photoreceptors. Photoreceptors give box jellyfish the ability to detect light from dark, but it is uncertain whether this species can process shapes and figures. Box jellyfish, however, are attracted to light and tend to avoid darker shapes. Box jellyfish can also detect vibrations, which is thought to be useful for finding prey and avoiding predators. Currently, little is known regarding methods of communication between jellyfish. If box jellyfish do communicate with one another, it is most likely through chemical signals.

Perception Channels: visual ; vibrations

After the reproduction of sexually mature medusa, box jellyfish develop planulae, cells grouped together after fertilization. Planulae soon develop into polyps, which are sessile and small (1 to 2 mm) and look like a living ball with two tentacles. Polyps use their two tentacles to attach to a hard surface, such as a stone or the shell of other animals. Polyps usually attach themselves to a surface where they are not exposed, often on the underside or a crevice of the hard surface. Polyps rely on schools of plankton for food. A polyp can reproduce asexually via budding. After a polyp has metamorphosed into a small medusa, it travels from freshwater rivers to the sea. Once in the sea, a maturing box jellyfish continues to grow until it reaches its full size of 16 to 24 cm.

Development - Life Cycle: metamorphosis

Because box jellyfish die shortly after spawning, their lifespan is thought to be under a year. The longest lived box jellyfish in captivity survived nine months. Until the invention of a modified tank in the 1990s, it was near impossible to keep box jellyfish alive in captivity for more than a few days. Water is in constant motion in new tanks, allowing box jellyfish to float in the current without being caught in the corners of the tank.

Range lifespan

Status: captivity: 9 (high) months.

Box jellyfish find mates by swimming to freshwater rivers during the spring. Here, jellyfish release their sperm and eggs directly into the water. Shortly after spawning, box jellyfish die.

Every spring, box jellyfish gather to spawn in rivers and similar bodies of water. Mature box jellyfish release sperm or eggs into the water. Once fertilization occurs, planula attach to a hard surface and develop into a small polyp, which may asexually reproduce via budding. Once the polyp has finished budding, it develops into a juvenile medusa, which grows into a sexually mature medusa.

Breeding interval: Box jellyfish breed once a year.

Breeding season: Box jellyfish breed from late summer to early fall.

Average age at sexual or reproductive maturity (female): 2 months.

Average age at sexual or reproductive maturity (male): 2 months.

Key Reproductive Features: seasonal breeding ; sexual ; asexual ; oviparous

Mature box jellyfish die soon after the release of sperm and eggs and, as such, do not invest in the upbringing of their offspring.

Parental Investment: no parental involvement

Jellyfish deliver deadly toxins to enemies and prey via special stinging cells, called nematocysts.

Box jellyfish are not considered at risk by the IUCN, CITES, or the US Federal List. Furthermore, there are no conservation efforts for box jellyfish.

US Federal List: no special status

CITES: no special status

Box jellyfish are believed to be the most venomous creatures in the world. Their stings are extremely deadly to human beings, and have caused over 60 deaths in the last century. The amount of venom injected into humans by box jellies influences the certainty of death. It is estimated that if a total of 6 m of tentacles comes into contact with human skin - and therefore all nematocysts on those tentacles “fire” - the amount of venom injected is sufficient to cause death in just a few minutes. Shortly after a human is stung, they typically encounter symptoms such as extreme pain, shortness of breath, and purple welts. Some victims may also become irrational and suffer cardiac arrest. All of these symptoms typically commence within five minutes of being stung and can last up to two weeks before subsiding. Although box jellyfish are fully capable of killing adult humans, most fatalities are documented in children and young adults. To reduce fatalities, box jellyfish nets have been constructed on many beaches where box jellyfish stings are known to occur. Despite these nets, there are still reports of stings every year.

Negative Impacts: injures humans (bites or stings, venomous )

The study of box jellyfish venom has led to a successful anti-venom agent, which can save human lives if administered quickly. Additionally, while this research is still in its infancy, scientists hope to better understand why jellyfish venom is so harmful to the human cardiovascular system. Once determined, this information can hopefully be used to design more effective medicine for other cardiovascular problems.

Positive Impacts: source of medicine or drug ; research and education