Chironex fleckeri

The Chironex fleckeri is a box jellyfish commonly referred to as the marine stinger. It is best known for its dangerous venom within its tentacles that claims one life a year in Australia. Generally, it lives in shallow waters near Australia and can cause many problems for humans. It is sometimes seen as a cold-blooded killer that preys on humans but in truth it is not and only reacts to the chemicals on humans. They are characterized by their bell-shaped body and many long tentacles extending from their body.

Anatomy
The Chironex fleckeri has two different body plans called a polyp and medusa. Both of these body plans are radially symmetrical, and have a mouth in the center of the body surrounded by tentacles. They also both have a gastrovascular cavity lined with gastroderm and surrounded by a body wall, this is where digestion of food takes place. They are covered on the outside by epidermal tissue and below that layer of tissue is the mesoglea which is a thin membrane. The polyp is the larval stage of the Chironex fleckeri, it has a cylindrical body with the mouth/anus pointed upwards along with the tentacles. The medusa stage has a bell-shaped body with mouth/anus and tentacles pointing downward.(Miller and Levine p670) A fully grown medusa can have up to 60 total tentacles and they may be as long as 180 meters. These tentacles contain stinging cells called cnidocytes all over them. In every cnidocyte is a nematocyst which is a coiled dart filled with poison that shoots into the prey and injects venom. The venom contained in the Chironex fleckeri's stinging cells is highly dangerous to both animals and humans. The Chironex fleckeri gathers information through a network of nerve cells throughout it's body called a nerve net. Included in this nerve net are cells called statocysts that find the direction of gravity and cells called Ocelli which are eyespots that detect light. The Chironex fleckeri has muscle tissues in it's body for movement, when it contracts these muscles, it forces water out of its body and is propelled forward.

Reproduction
The Chironex fleckeri reproduces both sexually and asexually. When it is a polyp, it can reproduce asexually through a process called budding. Budding is accomplished when a part of the polyp begins to swell and grows then eventually breaks off of the polyp creating a new one. This new polyp is genetically identical to the polyp that it grew off of. The Chironex fleckeri reproduces sexually in its medusa stage.(Miller and Levine p672) The male releases sperm into the surrounding water and it is absorbed by females and reaches the ovary. This fertilizes the eggs forming a zygote and it is released into the water. The zygote forms into a swimming larva called a planula which finds its way to the sea floor and attaches itself to a rock or other hard surface and develops into a polyp thus beginning the process again.

Ecology
The Chironex fleckeri population resides primarily in the tropical waters surrounding Australia particularly the northern Australian coast but they have been sighted as far as the Philippines and Vietnam. They hunt small fish and prawns in shallow water near beaches which is why humans come into contact with them so often. The polyps of the Chironex fleckeri can be found attached to rocks in rivers and streams near the ocean. Not much is known about the population and habits of the Chironex fleckeri because of its transparency and increased activity at night make it elusive and hard to spot.

Threat to Swimmers
The Chironex Fleckeri contains very powerful and often deadly venom in it's stingers. About 1 death a year in Australia has been attributed to Chironex fleckeri encounters. On the beaches in Australia signs are posted warning swimmers of box jellyfish in the waters. Swimmers are stung by the Chironex fleckeri when they come into contact with it's tentacles. When the skin passes over the tentacles it activates the cnidocytes which propels the nematocysts into the skin injecting the venom. The symptoms of the venom are quite severe. After you have touched the tentacles, there is a sudden pain on the skin, like an intense burning sensation. Victims often react violently and thrash in the water, ripping the tentacles from the jellyfish and wrapping it around themselves which results in more severe stinging. Frequently, victims try to pull the tentacles from their skin which ends up causing more harm than good by stinging their hands. Running from the beach and thrashing in the water increases the heart rate and allows the venom to travel through the body more rapidly which results in more severe symptoms. The venom specifically attacks nerves, the heart, and skin. Within 12-18 hours of the sting the skin affected by the venom begins to die and turn to a darker red and blistering might appear. Women and children have a higher chance of being stung worse then men because hair protects against some of the venom and women and children generally have little hair on their body. The Chironex fleckeri never intentionally stings humans but when stimulated by chemicals on our bodies they release thier nematocysts inject us with venom.