The box jellyfish is an invertebrate in the class Cubozoa. It gets both its common name and class name for the boxy shape of its bell. However, it's not actually a jellyfish. Like true jellyfish, it belongs to the phylum Cnidaria, but a box jellyfish has a cube-shaped bell, four sets of tentacles, and a more advanced nervous system.
Fast Facts: Box Jellyfish
- Scientific Name: Cubozoa
- Common Names: Box jellyfish, sea wasp, Irukandji jellyfish, common kingslayer
- Basic Animal Group: Invertebrate
- Size: Up to 1 foot diameter and 10 feet long
- Weight: Up to 4.4 pounds
- Lifespan: 1 year
- Diet: Carnivore
- Habitat: Tropical and subtropical oceans
- Population: Unknown
- Conservation Status: Not evaluated
Cubozoans are easily recognized by the square, boxy shape of their bell. The edge of the bell folds in to form a shelf called a velarium. A trunk-like appendage called a manubrium sits near the center of the underside of the bell. The end of the manubrium is the box jellyfish's mouth. The interior of the bell contains a central stomach, four gastric pockets, and eight gonads. One or more long, hollow tentacles descend from each of the four corners of the bell.
The box jellyfish has a nerve ring that coordinates pulsing required for movement and processes information from its four true eyes (complete with corneas, lenses, and retinas) and twenty simple eyes. Statoliths near the eyes help the animal discern orientation with respect to gravity.
Box jellyfish size depends on species, but some can reach 7.9 inches wide along each box side or 12 inches in diameter and have tentacles up to 9.8 feet in length. A large specimen may weigh 4.4 pounds.
SpeciesNearly microscopic box jellyfish. Billy Huynh / Getty Images
As of 2018, 51 box jellyfish species had been described. However, undiscovered species likely exist. The class Cubozoa contains two orders and eight families:
- Family Alatinidae
- Family Carukiidae
- Family Carybdeidae
- Family Tamoyidae
- Family Tripedaliidae
- Family Chirodropidae
- Family Chiropsalmidae
- Family Chiropsellidae
Species known to inflict potentially lethal stings include Chironex fleckeri (the sea wasp), Carukia barnesi (the Irukandji jellyfish), and Malo kingi (the common kingslayer).
Habitat and Range
Box jellyfish live in tropical and subtropical seas, including the Atlantic Ocean, eastern Pacific Ocean, and Mediterranean Sea. The highly venomous species are found in the Indo-Pacific region. Box jellyfish occur as far north as California and Japan and as far south as South Africa and New Zealand.
Box jellyfish are carnivores. They eat small fish, crustaceans, worms, jellyfish, and other small prey. Box jellyfish actively hunt prey. They swim at speeds up to 4.6 miles per hour and use stinging cells on their tentacles and bell to inject venom into their targets. Once prey is paralyzed, the tentacles bring food to the animal's mouth, where it enters the gastric cavity and is digested.The box jellyfish digests prey in the stomach inside its bell. Damocean / Getty Images
Box jellyfish also use their venom to defend against predators, which include crabs, batfish, rabbitfish, and butterfish. Sea turtles eat box jellyfish and appear to be unaffected by the stings. Because they can see and swim, box jellyfish appear to behave more like fish than jellyfish.
Reproduction and Offspring
The box jellyfish life cycle involves both sexual and asexual reproduction. Mature medusae (the "box" form) migrate to estuaries, rivers, and marshes to breed. After the male transfers spermatophores to the female and fertilizes her eggs, her bell fills with larvae called planulae. The planulae leave the female and float until they find a solid attachment site. A planula develops tentacles and becomes a polyp. The polyp grows 7 to 9 tentacles and reproduces asexually by budding. It then undergoes metamorphosis into a juvenile medusa with four primary tentacles. The time required for metamorphosis depends on water temperature, but is around 4 to 5 days. The medusa form reaches sexual maturity after 3 to 4 months and lives about one year.
The International Union for Conservation of Nature has not evaluated any Cubozoan species for a conservation status. Generally, box jellyfish are abundant within their range.
Box jellyfish face the usual threats to aquatic species. These include climate change, severe weather, prey depletion from overfishing and other causes, pollution, and habitat loss and degradation.
Box Jellyfish and HumansVinegar is the most common treatment for jellyfish, box jellyfish, and man o' war stings. Mataya / Getty Images
Although the box jellyfish is the world's most venomous animal, only a few species have caused fatalities and some species are considered harmless to humans. The largest and most venomous box jellyfish, Chironex fleckeri, is responsible for at least 64 deaths since 1883. Its venom has an LD50 (dose which kills half the test subjects) of 0.04 mg/kg. To put that into perspective, the LD50 for the highly venomous coral snake is 1.3 mg/kg!
The venom causes cells to leak potassium, resulting in hyperkalemia that potentially leads to cardiovascular collapse within 2 to 5 minutes. Antidotes include zinc gluconate and a drug developed using CRISPR gene editing. However, the most common first aid treatment is removal of tentacles followed by application of vinegar to the sting. Dead box jellyfish bells and tentacles can still sting. However, wearing pantyhose or lycra protects against stings because the fabric serves as a barrier between the animal and the skin chemicals that trigger a response.
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