8 Mind-blowing Facts About Box JellyfishReading time: 4 minutes
1. Box jellyfish have eyes very similar to our own…
Despite their lack of brains, blood, or even hearts, box jellyfish or cubozoans (meaning ‘cubed animals’) are astoundingly well-equipped in the eye department. Their remarkably advanced eyes have lenses, retinas and corneas very similar to our own.
Image credit: Dr. John Anderson
2. …which are permanently out of focus…
Jellyfish do not have brains, just a ring of nerves around their mouths. As such they have no central processing power meaning their vision is always blurry.
3. …and there are 24 of them!
Each box jellyfish has 24 fully functioning eyes. These are grouped into four clusters called rhopalia located on each side of their cube-like body. This allows box jellyfish to have 360 degrees field of vision. Each of the four clusters has two of the remarkably advanced eyes mentioned above and four eyes which are simple pits containing light-sensitive pigments.
4. Box jellyfish go to bed at 3pm…
Box jellyfish ‘sleep’ for roughly 14 hours every day. Researchers in Australia have use ultrasonic tagging and found that box jellyfish lie motionless on the ocean floor between 3pm and dawn in an effort to conserve energy and avoid predation. During this period no bell pulsation occurs and all tentacles are completely relaxed and in contact with the sea floor.
5. …And they hate being woken up!
Jellyfish are light sleepers. Following a small disturbance such as a beam of light or a vibration a box jellyfish will quickly rise from its slumber, swim around for a short period, and then fall back into an inactive state on the ocean floor. This is again to avoid predation and during this period an accidental sting to any surrounding disturbance e.g. a clumsy foot is much more likely to occur.
6. Unlike other jellyfish they can swim (and swerve)
Unlike true jellyfish, which drift in the current hoping for food to swim in their direction, box jellies can swim at speeds of up to 6 feet per second and typically cover around 200m per hour during the daytime. They can also steer around obstacles. As such they have an unlikely ability to ‘hunt’ for prey.
7. One species of box jellyfish is probably the most poisonous creature on earth…
The sea wasp (Chironex fleckeri) is the most venomous species of box jellyfish and maybe also the most poisonous species on earth. It’s sting produces immediate excruciating pain followed by an intense burning sensation. Death can occur within 3 minutes with the venom producing a powerful three-pronged attack on the victims nervous system, heart and skin. Approximately 10,000 people are stung each year by box jellies and estimates suggest around 100 people die each year from the stings delivered by the many species of box jellyfish (~40 known) with 20-40 deaths occurring annually in the Philippines alone.
Image credit: Smarter Every Day
8. …and another species is just as bad
The box jelly known as Carukia barnesi is transparent and about the size of a peanut making it virtually invisible in the water column. What’s more it is nearly as toxic as the sea wasp and it’s entire body is coated in stinging cells. The sting from this jellyfish has been known to cause an illness known as ‘Irunkandji syndrome’ for those who survive it’s potent sting. Symptoms of the syndrome include intense pain, nausea, vomiting, catastrophically high blood pressure and a feeling of impending doom. Perhaps most importantly the venom causes a massive release of the fight-or-flight hormone noradrenalin which can often cause victims to ‘panic’ to death.
So why are these box jellyfish so venomous? Although blurred, the sight that box jellies have gives them a real advantage in determining edible prey. This allows them to eat things much larger than themselves. In order to minimise damage to their own delicate tentacles they need to paralyse their prey immediately.
Featured image credit: Joshua Lambus Flickr