Structure
The Portuguese man o' war is composed of four types of polyp. One of the polyps, a gas-filled bladder called the pneumatophore (commonly known as the sail), enables the organism to float. This sail is bilaterally symmetrical, with the tentacles at one end, and is translucent, tinged blue, purple, pink or mauve. It may be 9 to 30 centimetres (4 to 12 in) long and may extend as much as 15 centimetres (6 in) above the water. The gas that the Portuguese man o' war secretes into its sail has approximately the same composition as the atmosphere, but may build up a high concentration of carbon dioxide (up to 90%). The sail is equipped with a siphon. In the event of a surface attack, the sail can be deflated, allowing the man o' war to briefly submerge.
The other three polyp types are known as dactylozooid (defence), gonozooid (reproduction), and gastrozooid (feeding). These polyps are clustered. The dactylzooids make up the tentacles that are typically 10 metres (30 ft) in length but can be up to 50 metres (165 ft). The long tentacles "fish" continuously through the water, and each tentacle bears stinging, venom-filled nematocysts (coiled, thread-like structures), which sting and kill small sea creatures such as small fish and shrimp. Contractile cells in each tentacle drag the prey into range of the digestive polyps, the gastrozooids, which surround and digest the food by secreting enzymes that break down proteins, carbohydrates and fats. Gonozooids are responsible for reproduction.
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