The animals are usually symmetrical, their symmetry being usually radial, and their body is cup- or bell-shaped, with a crown of tenticles bearing stinging cells or nematocytes. As predators, they are designed to catch their prey, using their cnidoblasts, which are tiny blisters from each of which projects a hair-like trigger, the cnidocil. When these are touched, the capsule opens and this allows a rolled-up tubular thread to be shot out. There are three types of threads: volvents - long threads which ensnare the prey; glutinants - sticky threads to hold prey fast; and penetrants - tubular threads which have spines at the base or all along them which penetrate the skin of the prey or attacker and secrete a paralysing and stinging substance (hypnotoxin). Capsules of all three types are commonly distributed over the whole body surface of these animals. They are always present on the tenticles, and there they are often massed in dense groups. They can only be used once, and then they have to be replaced.

There are more than 9000 known species in the three classes of Hydrozoa, Scyphozoa and Anthozoa (hydroids, jelly-fish and sea-anemones). The phylum Ctenophora contains about 100 species of mainly pelagic marine animals. There are two main categories: those with tenticles (Tenticulata) having two main tenticles, and those without (Nuda). The main caching threads of the tentacles, together with variously formed subsidiary threads and colloblasts, can be retracted into pockets.

Clinical Features: Stings from a coelenterate cause severe burning pain and a red welt - or a row of lesions - at the site of the sting. The initial lesions appear as small papular eruptions in one or several discontinuous lines, at times surrounded by an erythematous zone. The papules develop rapidly and the area becomes red and raised. Pain may be severe and itching is common. The papules may vesiculate and proceed to pustulation and desquamation, possibly leaving permanent scars. Some victims also suffer systemic manifestations including weakness, headache, nausea & vomiting, muscle cramps & pain, lacrimation & nasal discharge, increased perspiration, tacchycardia, diarrhoea, convulsions and brearthing problems. In the water, the initial shock of the sting may cause a swimmer to jerk away, which stimulates the tenticles to release more poison. On shore, more poison is released if the victim tries to rip off the sticky threads. One or two weeks after the sting, the victim may experience a recurrence of the lesion at the site, which can be treated with antihistaminics. In Malta, it is not particularly important to identify the type of coelenterate.

Treatment: Various remedies for coelenterate stings have been advocated. Alcohol, ammonia or vinegar poured over the site have been advocated to deactivate the tentacles, which should then be scaped off with a towel. Pull off - do not rub - the tentacles since these will continue to discharge their stinging nematocysts as long as they remain on the skin. Various substances have been advocated for pain relief, including baking soda, boric acid, lemon juice, gasoline, alcohol, calamine lotion, and meat tenderizer. These possibly work by changing the skin pH. The following procedures are recommended: sea water (not fresh water) is poured over the injured areas; the tenticles are then removed, preferably using forceps; alcohol is poured over the wounds and then flour or baking soda is applied to the sites; the applied material is then scraped from the wounds using an instrument and the areas are again washed with sea water. A topical corticosteroid is then applied, preferably by aerosol.

Jellyfish often cause allergic reaction, and the injured individual must be watched for signs of shock or breathing problems. More serious cases require additional therapeutic measures. Oxygen or respiratory assistance may be required. Painful muscle spasms may be relieved with 10 ml of 10% calcium gluconate given intravenously. Intravenous fluids and epinephrine or steroids may be needed for a few cases in which shock develops.