The Bluebottle or Portuguese Man-of-War is not a single animal but a colony of four kinds of highly modified individuals (polyps). The polyps are dependent on one another for survival.
The float (pneumatophore) is a single individual and supports the rest of the colony. The tentacles (dactylozooids) are polyps concerned with the detection and capture of food and convey their prey to the digestive polyps (gastrozooids). Reproduction is carried out by the gonozooids, another type of polyp.
The float is a bottle or pear-shaped sac that can exceed 15 cm. It is mainly blue, though its upper margin may show delicate shades of green or pink. It is a living, muscular bag that secretes its own gas, which is similar to air. The float has aerodynamic properties and it seems likely that sailing characteristics may be modified by muscular contraction of the crest. Physalia sails at a slight angle downwind and the course is determined by 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 vice versa. 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 are the 'stomachs' of the colony and respond quickly to the presence of food, wriggling and twisting until they fasten their flexible mouths to it. Once attached they become all mouth, spreading out over the surface of the morsel. The resting polyp measures only 1-2 mm in diameter but the mouth may expand to more than 20 mm. They digest the food by secreting a full range of enzymes that variously break down proteins, carbohydrates and fats.
The most impressive members of the colony are the tentacles. As Physalia drifts downwind, the long tentacle fishes continuously through the water. Muscles in the tentacle contract and drag prey into range of the digestive polyps. The prey consists mostly of small crustaceans and other members of the surface plankton which it ensnares in a tangle of nematocyst threads.
Nematocysts are among the most complex intracellular structures known and may be only 0.001 mm in diameter. Each is a hollow sphere with its external wall turned in at one point as a long, hollow, coiled thread or tube turned outside in. The opening left in 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 is usually armed with spines or barbs that aid in the penetration of, and anchorage in, 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, so each individual gonozooid consists of male and female parts. The fertilised egg develops into a planktonic larval form which produces the large Physalia colony by asexual budding.
The Bluebottle belongs to the phylum Cnidaria, which includes corals and sea anemones. Two other floating colonial cnidarians which may be found with Bluebottles are the By-the-wind sailor (Velella) and the blue-green Porpita pacifica. The float of Velella is a flat, oval disc with many gas-filled tubes. It is about 5 cm across with a slender diagonal sail, allowing the animal to sail at an angle to the wind. The float of Porpita is a flat, circular disc up to 2.5 cm across with many gas-filled tubes, but no sail. Both of these species possess fishing tentacles with stinging capsules that have no effect on humans.
Bluebottle tentacles will cause a sharp, painful sting if they are touched, which is aggravated by rubbing the area. Intense pain may be felt from a few minutes to many hours and develops into a dull ache which then spreads to surrounding joints. The affected area develops a red line with small white lesions. In severe cases blisters and weals looking like a string of beads may appear. Victims may exhibit signs of shock. Children, asthmatics and people with allergies can be badly affected and many cases of respiratory distress have been reported in Australia.
If stinging occurs, leave the water immediately. If any part of the animal is still sticking to the skin, it should be gently lifted off with tweezers or a gloved hand. This will minimise the firing of more stinging capsules. Do not rub the area with wet sand or towel, or wash with alcohol as this will only make it worse. For milder stings, ice packs or local anaesthetic sprays are often effective in reducing pain. In extreme cases resuscitation may be needed and medical attention should be sought.
Bluebottles are not always obvious in the water. Tentacles may break away from the colony in the surf and inflict stings just as potent as those from attached tentacles. Even dead specimens stranded on the beach can still cause stings. To avoid being stung do not touch these animals with bare skin and do not enter the water if they are present. Bluebottles are more common on exposed ocean beaches after strong onshore winds and are rarely found in sheltered waters.
Copyright © Australian Museum, 2003
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