Blue bottle, Portuguese man-of-war

The Bluebottle is a colony of four kinds of highly modified individuals (polyps). Each of them is responsible for certain biological functions. The float (or pneumatophore) supports the rest of the colony). The tentacles (dactylozooids) hunt for prey and when they capture something, they pass it on to the digestive polyps (gastrozooids). Reproduction of the colony is performed by the gonozooids, another type of polyp.

The float resembles a bottle and can exceed 15 cm. It is primarily colored in blue (sometimes its uppermost part may be slightly green or pink). It secretes its own gas that is similar to air. Because the float is aerodynamic, it seems very likely that the course of sailing can be determined by muscular contractions of the crest. In fact, the bluebottle sails at a slight angle downwind and the course depends on the curvature of the float and the underwater resistance of the rest of the colony. The float may project either to the left or to the right; the left-handed forms sail to the right of the wind and the right-handed forms sail to the left. Thus, if the sailing angle of one form leads to its stranding on the shore, the others sailing to the opposite side of the wind may escape.

The digestive polyps quickly detect the presence of food. They have very flexible mouths. When the food is already attached to them, the polyp spreads over the surface of the prey. The resting polyp is only 1-2 mm in diameter but its mouth may expand to more than 20 mm. In the digestion of the food a number of  enzymes are involved that variously break down proteins, carbohydrates and fats.

The tentacles are very impressive. As Physalia  sails, the long tentacle fishes continuously through the water. It catches prey by means of muscle contractions and drags it to the digestive polyp. The bluebottle favorite food are various members of the surface plankton, which it entangles in nematocyst treads. Nematocysts are very complex intracellular structures. They may be only 0.001 mm in diameter. Each is a hollow sphere. Its external wall is turned in at one point and resembles a long, hollow, coiled thread or tube turned outside in. The opening left on the surface of the capsule is covered by a hinged lid held down by a hairlike trigger. When the stinging capsule is stimulated the tube shoots outward turning itself right side out. The tube usually has numerous spines or barbs that aid in the penetration of the victim's flesh. Stinging capsules contain a toxic mixture of phenols and proteins that is injected into the victim through a terminal pore in the thread.

Bluebottles are hermaphrodites (each individual gonozooid has male and female parts). The fertilized egg develops into a planktonic larval form that produces the large Physalia colony by asexual budding.

First Aid
The tentacles will cause a sharp, painful sting when touched. Rubbing the affected area with a towel or wet sand could only make things worse. Intense pain is felt, which grows into a dull ache spreading to the surrounding joints. The stung area becomes red and small white lesions appear. In severe stings, scars and blisters may occur. The sting of a bluebottle is especially dangerous to children, elderly people, asthmatics and people with allergies as it can cause respiratory distress.

The victim should leave the water immediately. If parts of the animal are still sticking to the skin, they should be gently removed with tweezers or a gloved hand. This will minimize further firing of stinging capsules. Use of vinegar is not recommended. Milder stings can be well treated with ice packs and anaesthetic agents for reducing pain. In extreme cases resuscitation may be required. 
Bluebottles cannot always be easily distinguished in seawater. Some tentacles may break away from the colony and their stings are not milder than those of the attached tentacles. The safest way to protect yourself is not to touch these animals with bare hands and not to enter water where they are present. Bluebottles usually frequent exposed ocean beaches after strong onshore winds. They are rarely found in sheltered waters.