Re: Are marine, terrestrial and fresh water planarians osmoconformers ?

Sorry Nuno Morais

we asked your question to several sicentist in our network, but they could not answer it. I am biologist since about 17 years and can not remember that I ever came accross the term "osmoconformer". I did a search on Current Contents and on medline for this term and both databases came up with not a single hit in any of the multi million articles covered. Did you get the term wrong?

Anyway, in principle every single living organism has to be in an environment that has a similar osmolarity than inside the cells, otherwise has to have mechanisms that keep the osmolarity inside the cells constant. Surprisingly all living cells have a osmolarity similar to seawater. Thus all marine organisms have little problems with keeping osmolarity of the body fluids constant. Any arganism outside seawater has to deal with that problem. In freshwater the olmolarity is well below the one inside the cells. They all have mechanisms preventing water to enter the body and to get rid of water entering the cells. In air the main problem is water loss, so all those organisms here have mechanisms to prevent water leaving the body. All organisms in salt lakes have the similar problem, they loose body fluid and have mechanisms to prevent that.

Hope that helps a little.
If not, try to rephrase your question, avioding the term "osmoconformer", so that we better understand what you are looking for.

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Admin note:
Richard Kingsley adds the following:

The term osmoconformer is widely recognized and used by biologists. An osmoconformer is an organism that allows its body fluid to have the same osmotic potential as its environment. Osmoregulatos descibes an organism that must maintain its body fluids at a different osmotic potential from its environment.

Freshwater planarians are osmoregulators and have protonephridia that actively absorb ions. I would suggest that Mr. Morais try some animal physiology texts as a starting point. These were recommended in the textbook that I have called LIFE.

Animal Physiology: Mechanisms and Adaptations by Eckert, Randall and Augustine

Animal Physiology: Adaptation and Environment by Schmidt-Nielson (1990)