Strange string jellies

Siphonophores or string jellies are another group of little known but beautiful deep sea critters.
12 December 2010

Interview with 

Gill Mapstone, Natural History Museum

Siphonophores or string jellies are another group of little known but beautiful deep sea critters.

Find out more:

Agalma elegans - a string jelly - at the Natural History Museum

Gill - My name is Gill Mapstone and I'm a scientific associate at the Natural History Museum in London. And I work on some rather unusual animals there, which are called siphonophores.

These are marine creatures which live mostly in the deep sea and often they are actually called string jellyfish or string jellies because they tend to look a bit like a string.

So they have a number of swimming bells at one end and these all pump together to push the animal forward by jet propulsion in a certain direction. And behind that you have more stem with serially reproduced mouths each with a tentacle and usually there's some sort of flotation structures called bracts which look a little bit like leaves. And also the reproductive organs in there. 

So, this part of the stem can actually go on for metres in some larger jellyfish. I think one of the largest siphonophores ever found was about 50 m long.

And, I'm interested in them because they are important predators in the sea. They eat a lot of fish larvae and things like that, which are of course important for humans. And also they're quite remote and difficult to access and if you can see them life from the submersible then they look really beautiful.

So, would you know any siphonophores if you saw them? Well, there is one that you probably have heard of but this is not actual typical at all of the group, and that is the Portuguese man of war, who's Latin name is Physalia.

It's very unusual because it's got a big float, it floats on the surface of the sea. Very few things can eat them, although actually turtles can. But they are pretty difficult to study because they're so venomous. And you don't really want to get entangled with one when you're swimming because they can have long tentacle which stretch underwater for some distance. 

And these can actually give you a very nasty sting and leave scars on your body. And if you're actually rather ill before you get a sting maybe, or predisposed to some problem, health problems, then you could actually be killed by one of those although that rarely happens. 

So that's the Portuguese man of war. Still we don't really know how many species there are in the sea. At the moment we think there's one but there may be another one because off Australia you get a smaller one called the blue bottle.

Anyway they are interesting animals, but the ones that I study are really more beautiful, I would say, and they live in deep water so they are really rather mysterious.

So actually they are really the most fascinating group of animals.


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