The infinite variety: the beginning of life
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Chironex fleckeri 
Chironex fleckeri is a highly venomous species of box jellyfish. For a jellyfish it is a very fast swimmer and has very sophisticated eyes. Chironex fleckeri grow to approximately the size of a basketball, is nearly transparent and has four clusters of 15 tentacles. When the jellyfish are swimming the tentacles contract so they are about 15cm long and as thick as bootlaces, when they are hunting the tentacles are thinner and about three metres long. The tentacles are covered with stinging cells or Nematocysts which are activated by pressure and a chemical trigger: they react to proteinous chemicals. The polyps are found in estuaries in northern Australia, the medusa is pelagic and is found in the coastal waters of northern Australia and adjacent areas of the tropical Indo-West Pacific, and are also found in southeastern Asia. They are not usually found on the reef. In common with other box jellyfish, Chironex fleckeri have four eye-clusters with twenty-four eyes. Some of these eyes seem capable of forming images, but it is debated whether they exhibit any object recognition or object tracking and it is not known how they process information from their sense of touch and eye-like light detecting structures. Chironex fleckeri live on a diet of prawns and small fish and are themselves prey to turtles. 
The Sting of Chironex fleckeri has killed about one hundred people in Australia over the last one hundred years, making it possibly the most dangerous species of jellyfish in the world. Chironex flickeri appear to avoid human beings when they are close to them and so can be said to avoid stinging humans. Their sting is incredibly powerful and can be fatal. The sting produces instant excruciating pain accompanied by an intense burning sensation, and the venom has multiple effects attacking the nervous system, heart and skin at the same time. While an appreciable amount of venom (about ten feet or three metres of tentacle) needs to be delivered in order to have a fatal effect on an adult human, the potently neurotoxic venom is extremely quick to act. Fatalities have been observed as little as four minutes after envenomation, notably quicker than any snake, insect or spider and prompting its description as the world's deadliest venomous animal. Although an antivenom exists, treating a patient in time can be difficult or impossible. Dousing a sting with vinegar immediately kills any venom which has not been activated, while rubbing a sting exacerbates the problem. Hydrozoa Hydrozoa 
Scientific classification Kingdom: Animalia Subkingdom: Metazoa Phylum: Cnidaria Class: Hydrozoa Owen, 1843 Orders Actinulida Capitata Chondrophora Filifera Hydroida Siphonophora Trachylina The Cnidarians are more common and have bodies clearly divided into two cellular layers, each layer one-cell thick. The outer layer of cells is the ectoderm whereas the inner layer is the endoderm. The individual cells of the ectoderm are specialized for various functions such as protection, secretion, defence and cell replacement whereas the endoderm is specialized for digestion, absorption and assimilation of food. The stinging cells (Cnidocytes) of the ectoderm are highly specialized and contain coiled threads inside. When food or an enemy comes near, the cell discharges the thread which is armed with spines like a miniature harpoon and often loaded with poison. These cells are often concentrated at the ends of tentacles. Cnidarians reproduce by releasing eggs and sperm into the sea. The fertilized egg first develops into a free swimming creature that is quite different from its parents. It eventually settles down at the bottom of the sea and develops into a tiny flower-like organism called a polyp which filter-feed with the aid of tiny-beating cilia. Eventually, the polyp bud in a different way and produce miniature medusae which detach themselves and once again become free-swimming. True jellyfish spend most of their time as free-floating medusae with only the minimum period fixed to the rocks as solitary polyp, whereas sea anemones do the reverse with most of their life spent attached to rock as solitary polyp. Yet other coelenterates exist as colonies of polyps which have given-up a sessile life and have become free-floating e.g. Portuguese Man O'War (Physalia). 
The Portuguese Man O' War (Physalia physalis), also known as the bluebottle, is commonly thought of as a jellyfish but is actually a siphonophore—a colony of four sorts of polyps. Portuguese Man O' War Portuguese Man O' War 
Scientific classification Kingdom: Animalia Phylum: Cnidaria Class: Hydrozoa Order: Siphonophora Family: Physaliidae Genus: Physalia Species: P. physalis Binomial name Physalia physalis (Linnaeus, 1758) Download 2.01 Mb. Share with your friends:
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