Genus: Physalia (Bluebottle, Portuguese man-of-war)

Life > Eukaryotes > Opisthokonta > Metazoa (animals) > Cnidaria > Hydrozoa > Siphonophora

Bluebottles float around in the ocean and are notorious for their long tentacles (up to 10 m long) that sting people swimming in the water. Each bluebottle consists of a colony of individuals that function together as a single integrated animal.

Bluebottle (Physalia) washed up on beach [Photo H. Robertson, Iziko ©]

Close-up of floating Bluebottle [Photo G. Williams ©].

A bluebottle consists of a collection of individual animals morphologically developed for specific functions: there is the individual that develops as the floater, those that catch prey (dactylozoids), those that digest the prey (gastrozoids) and those that undertake reproduction (gonozoids). As the individuals making up a bluebottle are clones of each other (i.e. have identical genes), it is debatable whether a bluebottle should be viewed as an individual animal or as a colony of animals with highly evolved social adaptations. The floater is capable of movement, necessary to enable it to twist and dip drying parts of the float in the water. 

The dactylozoids, otherwise termed tentacles, can extend from 10 cm to up to 10 m long and can hence easily wrap themselves round their prey (e.g. fish) and discharge their sting cells (nematocysts). The tentacles then contract to bring the prey up to the gastrozoids, which fasten on to their prey with their sucker-like mouths. The gastrozoids discharge digestive enzymes to break down the tissue of the prey and the liquid food is then sucked in and transmitted to other individuals via a series of internal canals. The gonozoids focus exclusively on reproduction and utilize the food supplied by the gastrozoids to manufacture eggs and sperm. 

Bluebottles are capable of inflicting a painful sting, the result of the discharging of a large number of stinging cells (nematocysts) simultaneously when the tentacles make contact with your body. In the event of being stung, treat the skin with vinegar and apply ice. Severe cases can affect the blood flow and breathing necessitating medical treatment with antihistamines and steroids.  

The nudibranch Glaucus and the purple-shelled snail Janthina eat bluebottles out at sea. Those that get washed up on the beach are devoured by plough shells (Bullia species). 

References

• Branch, G. and Branch, M. 1981. The living shores of southern Africa. C. Struik Publishers, Cape Town.

• Branch, G.M., Griffiths, C.L., Branch, M.L. & Beckley, L.E. 1994. Two Oceans. A guide to the marine life of southern Africa. David Philip, Cape Town.

Text by Hamish Robertson