Carukia barnesi(Irukandji) is a small box jellyfish about 25 mm across its bell. It has a single, retractile tentacle (50-500 mm long) attached at each of the four corners of its bell. The Irukandji is like other carybdeid jellyfish in that its nematocysts (stinging cells) cover not only its tentacles, but also its bell. The Irukandji’s venom is particularly potent and causes a set of symptoms known as ‘Irukandji Syndrome’ in humans. Very little is known about this small transparent jellyfish’s biology. So far it has been reported only from the tropical waters off Northern Australia.
Carukia barnesi can be found along the coastline of Northern Australia, from Broome along the western side of Australia to Rockhamptom, Queensland on the eastern side. This includes Port Douglas in North Queensland to the Whisunday Islands near Mackay. It is also found in the Cairns regions and the Great Barrier Reef.
Biogeographic Regions: australian (Native )
The Irukandji jellyfish is a carybdeid cubazoan, which tend to be smaller than the other type of cubozoa, the chirodropids. Individuals of this species typically reach 25 mm in diameter, however it has been documented at a diameter of 35 mm. Carukia barnesi consists of a transparent bell that is cuboidal in shape that narrows slightly towards the apex. Extending from each of the four corners of the bell is a retractable tentacle that varies in length from 50 to 500 nm. Both the tentacles, as well as the body, are covered in stinging cells called nematocysts, however, the type of stinging cells differs on these two parts of the body. This box jelly also has a primitive and transparent eye on each side of its bell.
Range length: 20 to 35 mm.
Average length: 25 mm.
Other Physical Features: ectothermic ; radial symmetry ; polymorphic ; venomous
Carukia barnesi, unlike its congener Chironex fleckeri, is typically found in deeper waters along reefs.
Range depth: near surface to 10-20 m.
Habitat Regions: saltwater or marine
Aquatic Biomes: reef ; coastal
As C. barnesi matures, its diet switches from invertebrates to vertebrates. Box jellyfish in general utilize a toxin to paralyze their prey. The toxin is injected into the prey by the prey triggering one of the stinging cells (nematocysts) on the jellyfish’s tentacle. Once the stinging cell is triggered, a harpoon looking coil is released which stings the prey and the toxin then flows through this hollow harpoon into the prey. The tentacle can then be retracted back into the jellyfish, bringing the prey with it towards the jellyfish’s mouth, which is located inside the bell.
Animal Foods: fish; other marine invertebrates
Primary Diet: carnivore (Piscivore , Insectivore , Eats non-insect arthropods, Eats other marine invertebrates)
The role of Carukia barnesi in its ecosystem is currently not known.
Irukandji jellyfish are small and colorless, making them difficult to find.
Anti-predator Adaptations: cryptic
Life History and Behavior
Carukia barnesi have image-forming eyes that respond to images, but have no brain to process the visual information.
Perception Channels: visual
Cubozoans have a two-stage life cycle consisting of a medusa and polyp. Fertilized eggs develop into swimming planulae, which settle after a few days. The planulae develop into motile feeding polyps, which produce other budding polyps. Polyps take a few months to mature, then begin metamorphosis by resorbing tentacles. Four new tentacles and four rhopalia are formed. When the single juvenile medusa has fully metamorphosed, it contracts and swims away.
At this time the lifespan of Carukia barnesi is not known.
The mating system of the Irukandji jellyfish has yet to be recorded, but in some cubazoan species the adults release both sperm and eggs into the ocean where fertilization will occur.
Mature females of Carukia barnesi are defined as having fully developed oocytes. This typically occurs when the bell height exceeds 8 mm. Males are considered mature when bell height is comparable to that of mature females.
Key Reproductive Features: sexual ; fertilization (External )
At this time there is no known parental care.
Parental Investment: no parental involvement
Carukia barnesi has not been given special conservation status.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
Relevance to Humans and Ecosystems
Usually about 30 minutes after a person is stung by C. barnesi the victim begins to experience the following symptoms: a severe back or headache, shooting pain throughout the muscles in their chest and abdomen, nausea, anxiety, restlessness, and sometimes vomiting. Occasionally fluid may fill the lungs, which if not treated could be fatal. These symptoms can last from hours to days and requires hospitalization. No conclusive information has been obtained regarding the contents of the venom, but it might contain a neurotoxin that is a neural Na+ channel activator. No antivenom has yet been developed for this species.
Negative Impacts: injures humans (bites or stings, venomous )
There is no known human benefit from this species except that it serves to be an interesting research specimen because of the symptoms it causes when a person is stung.
Positive Impacts: research and education
Carukia barnesi is a small and extremely venomous jellyfish found near Australia. Stings can result in Irukandji syndrome, and thus this species is commonly known as Irukandji jellyfish, although this name does not distinguish it from other Irukandji jellyfish such as Malo kingi.
A mature C. barnesi's bell is only 12 by 30 millimetres (0.47 by 1.18 in) in height. It has four contractile tentacles, one extending from each bottom "corner" of its bell, ranging in length from 5 to 50 centimetres (2.0 to 19.7 in).
The species was discovered by Dr. Jack Barnes of Cairns, Australia, who, while on an exploration mission aimed at determining the reason for Irukandji syndrome, allowed himself to be stung by the jellyfish, while his 14-year-old son and a lifeguard looked on. The jellyfish was later named after him.
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