The Illustration Friday topic is Float this week.
A good topic I thought -at least i could think of a lot of different options right away: balloons and bubbles, ice cream floats, fishing floats, ice bergs, dandelion seeds, swim aid, a carnival float - lots and lots of possibilities.
However i after musing on these possibilities for a short while I decided that the the thing that really sums up 'float' for me is the Portuguese man O'War , Physalia.
The Portuguese man O'War isn't a jelly fish though it ressembles on superficially, in that it has trailing tentacles which sting and a jelly like 'head' . However a Portuguese man O'War is actually a different kind of thing altogether as it isn't actually a single organism -its a siphonophore , a colony of 4 different kinds of specialised organisms [polyps] that have the appearance of a single creature.
The Portuguese man O'War does not propel itself through the water like most jelly fish, but floats on top of the water, held up by its balloon-like float. The edge of the float acts as a sail and so the colony drifts with the wind and tides.
The float part, pneumatophore, is actually a single polyp that is filled with gas. The tentacles are each individual polyps called dactylozooids. These tentacles contain nematocysts which are the stinging cells containing a very dangerous toxin which has been known to kill humans, although it is more common to have a severe rash and excruciating pain; though sometimes the wounds will scar.
The tentacles trail in the water fishing for prey and they are able to contract and drag the poisoned prey to the digestive polyps , the gastrozooids.
The fourth type of polyp in the colony deals with reproduction, the gonozooids.
I have seen a few Portuguese man'o wars and i remember the first time i ever saw one. I was probably about 12 and sitting in a rowing boat ,trailing my hands in the sea water. The old fisherman who was rowing whacked me on the arm when he saw the distinctive sail of the Portuguese man o'war. I was a bit shocked and couldn't understand what the danger was as the creature looked like a piece of frosted glass or maybe a carrier bag floating on the water.
Its hard to imagine that something so weirdly beautiful can have such serious implications. However, the tentacles can trail for up to 50 metres from the float sail, so he was right to be cautious. Also the tentacles can easily break off and still sting- even when unattached to the central float.
People used to suggest ammonia solutions, vinegar or even human urine for man o' war stings but it seems that these treatments can all cause further damage and that an ice pack is often the best treatment - though anti-histamines or even adrenaline [eg from an epi-pen] and resuscitation may be necessary if the person has a severe reaction.
Sea turtles are the major predators of portuguese man o'war and apparently the turtles can be killed by eating floating plastic which looks sufficiently like a man o'war to a turtle.