Distribution

1. Tropical Atlantic, Mediterranean
2. Indo-Pacific.

In recent years, jellyfish with several tentacles (→ P. physalis?) have been sighted in various regions of the Indo-Pacific.


Fig. 4.14 Physalia utriculus

Biology

Portuguese men-of-war are not true jellyfish. They give the impression of being a single organism, but actually consist of a functional unit of many individuals with different functions. One end of the colony is shaped into the gas-filled bladder. It is not formed by a partial organism, as was long thought. This so-called pneumatophore, which floats on the water, keeps the colony afloat and functions as a "sailboat". In P. utriculus it usually has a length of 3–6 cm, in P. physalis up to 15 cm, and in strong winds may be tilted sidewards.

Below the pneumatophore there are many tentacles, predominantly those with reproductive polyps, but also others that contain defensive polyps covered in nematocysts. The latter type of tentacles are used to catch prey and when extended can reach a length of up to 20 m! These tentacles serve as a characteristic that distinguishes the two species, as P. physalis has several such tentacles and P. utriculus only has one. However, intermediate forms do appear to exist, and it is debatable if these are different species at all, as recently a number of jellyfish with several tentacles were found in the Indo-Pacific.

Portuguese men-of-war are generally carried in swarms over wide stretches of open water by wind and currents, and in this way can reach coastal waters in large numbers. On the east coast of Australia this usually occurs between October and March.

The tentacles leave long, whip-like marks on the skin. See Fig. 4.11 for the difference between these marks and those of Chironex or Charukia.

Risk

Of the most dangerous venomous marine animals, Physalia is in second place directly behind the box jellyfish. Envenoming due to P. physalis is generally more severe than that caused by the smaller P. utriculus. At least 3 fatalities due to P. physalis are known to have occurred on the US Atlantic coast. Accidents with P. utriculus are among the most common causes of jellyfish envenoming in Australia, but usually there are only strong local symptoms.

Literature (biological)

Burnett et al. 1987a, Cleland and Southcott 1965, Halstead 1988, Heeger 1998, Storch and Welsch 1997, Warrell and Fenner 1993, Williamson and Exton 1985, Williamson et al. 1996

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