BY Lewis Stagnetto, The Nautilus Project

Firstly, it isn’t a jellyfish! Although they look like jellyfish, which are Scyphozoans, box jellyfish form part of the Cuboza class and can be identified by their box shape and long tentacles sweeping down from each corner. Typically, these animals lack any pigmentation which can make them hard to see and like all Cnidarians, they sting.

The Australian version is definitely the most dangerous. A single sting could kill an adult in less than ten minutes and a single animal carries enough payload to kill 60 adults. The sting is really nasty too because it causes skin necrosis whilst inflicting excruciating amounts of pain. Not something you would choose to swim with!

Fortunately for us, scientists have now tested a drug which can prevent the necrosis, scaring and pain when it is directly applied on the affected area. Unfortunately though, further work is required to be certain that it will prevent the cardiac arrest that typically follows these initial symptoms.

Firstly, it isn’t a jellyfish!

Do we have them in the Mediterranean? Yes, but before you panic, the local species are not as venomous as their Australian cousins. They are still capable of delivering a nasty sting. The mediterranean species is called Carybdea marsupialis and can be distinguished from other species by some small red banding along the tentacles and the bell has some yellow wart like structures with stings cells on them.

An adult mediterranean box jellyfish can measure up to 3cm along the main bell area with its tentacles reaching around 30cm in length. Further, these animals are the fastest swimming of all the Cnidarians reaching speeds of up to 360 metres per hour. This is achieved using a simplistic jet engine design which squeezes water through a restricted aperture each time the animal pulses.

Some research suggests that they possess basic vision as they display obstacle avoidance behaviours and mimic ‘fish like’ behaviours. Yet other researchers claim they have sophisticated eyes with lenses and this is why they are so adept at avoiding objects within the water. It also suggests that these jellyfish actually have 2 different types of eyes: one that senses light and another which detects the colour and size of an object. It is claimed that the eyes can distinguish objects up to 10 metres away. Sophisticated stuff, considering it doesn’t have a brain.

Sophisticated stuff, considering it doesn’t have a brain.

As with most types of the true jellyfish, box jellyfish have two lifecycle stages. The sexes are distinct and produce gametes which fertilise in the water column. After fertilization a cubopolyp develops which has two stages, a mobile stage and a sedentary stage. The mobile phase comes first and the cubopolyp splits into pieces with each piece regenerating itself into a complete polyp. Once a complete polyp it settles out onto the substrate and begins growing.

Whilst in the sedentary phase, polyps develop 24 tentacles which they can use to feed. Around a month after settling, the end of the polyp buds off and the 24 tentacles are reabsorbed leaving only the recognisable four tentacles associated with the cubosa class.

A lesser known fact is that box jellyfish appear to sleep and have vertical migrations through the water column. During the day they rise up looking for food. They tend to prey on fish, arrow worms, annelid worms and crustaceans in general. Once fed, they return to deeper waters where they allegedly enter a catatonic state which resembles sleep.

Box jellyfish are by no means the top of their specific food chain either. As with a wide array of Cnidaria, box jellyfish are a favourite food of the Green turtle, Chelonia mydas, during its juvenile life phase. Green turtles can dive up to around 220 metres and consequently the box jellyfish are well within their reach during the daytime. Turtles will not be stung by these jellyfish due to the thickness and density of their skin, which prevents the stinging cells from envenoming even when inside their mouths.

Box jellyfish are not commonly found along the Gibraltar coastline, but their presence is definitively confirmed. The chances that a swimmer or beachgoer comes into contact with them is slim at best. Attempting to spot them is folly anyways. Typically referred to as the ‘sucker punch’ jellyfish most victims never see them coming. To my knowledge there has never been a single report of a box jellyfish sting in Gibraltar waters, and things are unlikely to change.

Regardless, the take-home message is that within the toxicity spectrum of the various venoms, the mediterranean box jellyfish carries the least payload!


Phylum: Cnidaria

Class: Cubosa

Habitat: Pelagic

Diet: Planktivore

Interesting Fact: Although related to them, Box jellies are not true jellyfish!

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