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Prepared By: Classification
Few marine creatures are as mysterious and intimidating as jellyfish. Though easily recognized, this animal is often misunderstood. Bathers and beachcombers react with fear upon encountering this invertebrate but, in fact, most jellyfish are harmless. There are around two thousand species of Jellyfish in the world but less than one hundred are considered dangerous to humans. Jelly Fish Biology in brief
Jellyfish are members of the phylum Cnidaria. Members of this structurally simple marine group possess one of two body forms. It displays radial symmetry with body parts radiating from a central axis. This symmetry allows jellyfish to respond to food or danger from any direction. Instead of a brain, "true" jellyfish possess an elementary nervous system, or nerve net, which consists of receptors capable of detecting light, odour and other stimuli and coordinating appropriate responses. Jellyfish occur in a wide variety of sizes, shapes and colors. Most are semi-transparent or glassy and bell-shaped, measuring less than an inch to over a foot across the bell, although some may reach 7 feet. The tentacles of some jellyfish can reach lengths greater than 100 feet. Regardless of their size or shape, most jellyfish are very fragile, often containing less than 5% solid organic matter. Jellyfish inhabit every major oceanic area of the world and are capable of withstanding a wide range of temperatures and salinities. Most live in shallow coastal waters, but a few inhabit depths of 12,000 feet.
The life cycle of a typical jellyfish involves an alteration of generations in which the animal passes through two different body forms. The dominant and conspicuous medusa is the familiar form, while the smaller polyp form is restricted to the larval stage. Jellyfish are either male or female and reproduce sexually. The adult jellyfish drifts in the water with limited control over its movements. However, it is, endowed with muscles that allow it to contract its bell, reducing the space under it, forcing water out through the opening. This pulsating rhythm allows for some regulation of vertical movement. Because jellyfish are sensitive to light, this vertical movement can be important Venom Apparatus Jellyfish are equipped with a specialized venom apparatus (cnidoblast) for defence and feeding. A capsule (nematocyst) inside the cnidoblast contains a trigger and a stinging structure. The stinging structure varies according to species, but generally consists of a hollow coiled thread with barbs lining its surface. Nematocysts are concentrated on the tentacles or oral arms. A single tentacle can have hundreds or thousands of nematocysts embedded in the epidermis. Contact of foreign object triggers and activate the nematocysts. Pressure within the nematocyst forces the stinging thread to uncoil rapidly. These thousands of nematocysts on tentacles act as small harpoons firing into prey, injecting paralyzing toxins. Stings usually paralyze or kill only small creatures but some jellyfish are harmful to humans also. Jellyfish do not "attack" humans normally. Stings occur when swimmers or beachcombers is exposed to nematocysts accidentally. Severity of stings depends on the following:
The majority of stings from jellyfish occur in tropical and warm temperate waters. However, most species are capable of inflicting only mild stings resulting in minor discomfort, except few, which are severely harmful. Harmful Jelly fish Few common harmful jellyfish are as follows: Chironex (Box Jellyfish ) Stings from Chironex Box Jellyfish have been recorded predominantly in coastal areas. A large but almost transparent jellyfish with a box-shaped bell (with four corners) up to 30 centimetres in diameter: Up to 15 ribbon-like tentacles arise from each of the four corners (up to 60 tentacles in total). These may contract to about 10 centimetres, or may extend up to 3 meters in length. Its sting causes severe burning skin pain, often with tentacles remaining on the stung area. Severe stings may cause the victim to stop breathing or their heart to stop. To treat the sting, pour vinegar on to sting.Irukandji Originally attributed to just one small jellyfish (Carukia barnesi), this term is now used to encompass a group of small carybdeids (box jellyfish with just one tentacle in each corner). Small transparent box jellyfish, 1–2 centimetres in diameter, usually never seen: some newly described species may be larger (up to 10 centimetres). This jellyfish causes an initial minor skin sting followed 20-40 minutes later by severe generalized muscular pain, headache, vomiting and sweating. The sting from some species can cause very high blood pressure that may be life threatening. These symptoms are sometimes referred to as Irukandji Syndrome. To treat the sting, pour vinegar on to sting.Physalia Found in most warm oceans worldwide, also known as Portuguese man of war. Has air-filled sac up to 10 centimetres in length, usually with a single, long blue tentacle hanging underneath. This may contract to a few centimetres, or extend to cover over a meter in length. Some species (Portuguese man-o'-war, Pacific man-o'-war) have many retractile tentacles and cause more severe stings. Wash area with seawater.Catostylus Found Worldwide. Common name is Blubber. Mushroom shaped bell 5-30 centimetres in diameter. Have no tentacles, but eight “fronds” or “frills” hanging underneath. The sting causes minor skin irritation.Cyanea found Worldwide. Common name Hair jelly, Snottie, Lions Mane. Large flat bell 4-30 centimetres in diameter with a large “mop” of fine hair-like tentacles 5-50 centimetres long. Bell top is usually white, but often with yellow or brown colouring under bell.Carybdea rastoni Transparent bell with 1.5-3 centimetres in diameter. Four tentacles, one in each corner, 5-15 centimetres long.Pelegia Common in the Mediterranean . Little Mauve Stinger. A small mushroom-shaped body from 4-12 centimetres in diameter. Unlike most jellyfish, the bell is covered with numerous warty lumps containing nematocysts (stinging cells). The bell is usually pink or mauve with eight pale brown tentacles 10-30 centimetres in length.Myths & Facts about jellyfish
TreatmentPrimary first aid for any jellyfish sting should be to minimize the number of nematocysts discharging into the skin and to reduce the harmful effects of the venom. If stung by a jellyfish, the victim should carefully remove the tentacles that adhere to the skin by using sand, clothing, towels, seaweed or other available materials. As long as tentacles remain on the skin, they will continue to discharge venom.
Prevention
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