How do Portugese-man-o-war jellyfish reproduce?

14 March 2010

Question

The syphonophore, the Portuguese man of war:

This is a collection of jelly fish each having its own individual function, catching food, digestion, movement, reproduction.

I can understand that the digestive jelly fish can feed the other jelly fish but if only one of the jelly fish reproduce, then how do the other jelly fish in the colony come about?
Have I got the facts wrong, or does the reproducing jelly fish produce all of the jelly fish?

Answer

We put this question to marine biologist Helen Scales...

Helen - Wonderful creatures indeed! Although keep your distance, of course, because they are nasty stingers, but they're beautiful things to look at.

I think this question is based on the fact that our listener knows that these animals are not in fact jellyfish. They're not single living creatures like that but they're colonies of lots of little creatures that live together.

They belong in the same phylum, the Cnideria, as jellyfish and they look similar but they are in fact different.

Portuguese man-o-wars are called siphonophores and they're made up of three main different types of little animals that live together.

There are dactylozoids, which make up the tentacles; there are gastrozoids, which are the bits that eat the food; and there are gonozoids, which are the bits of these creatures that reproduce. They produce sperm and eggs. In fact, you get female and male Portuguese man-o-war, even though they're called "Men"!

The sperm will fertilise eggs in the water column to produce larvae, which grow into bigger Portuguese man-o-wars.

The way that they grow from those individual cells is by asexual division of those cells and they produce all those individual three types of animals that live in this one colony and drift around the oceans, stinging things and eating things as they go.

Comments

How do all the "individuals" come together in the first place? Are they all hatched (or whatever) separately and then find each other and merge? (Which brings up a whole host of other questions such as, "what happens to individuals who don't find others to merge with?") Or are they somehow all born (or hatch or whatever) together? (Which brings up its own questions, such as "well, it's it really a colony of separate organisms of they all came into existence together at the same time?") Nobody is explaining this, well, much at all, let alone clearly so that the layperson can understand. What am I missing?

What Helen is saying here ("The way that they grow from those individual cells is by asexual division of those cells and they produce all those individual three types of animals that live in this one colony") is that the larval cells of the separate animals initially unite in the water column. They then grow by mitotic cell division (cells dividing in two) to grow the organism that you see.

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