"I simply cannot understand how a pivot (which involves half a complete turn)can be danced without the standing foot turning on the floor. I think this is anatomically impossible, but i am willing to learn!"
The action being danced should perhaps not really be called a pivoting action since the standing foot doesn't really pivot - instead it is a different action that seems to work better in pivot-like figures. Having your only standing foot rotating on the floor tends to put you in a fairly precarious position, which is perhaps why it is widely avoided.
As for how it's done, you should be able to turn out your moving leg 135 degrees from your standing foot without difficulty. And you should be able to turn in your standing foot 45 degrees while placing it. Add those up and what do you get? Also, even though the foot may pivot little if at all, you ankle can let the standing knee can dance across the foot as your weight arrives to, and then prepares to leave the inside edge.
And remember that you will drive towards the following step with your body and even foot alignments still quite underturned relative to your direction of travel.
"also, when it was stated that the body never stops moving, but the legs start and stop - this would mean detachable legs. so i think something slightly different was meant. Maybe the feet start and stop? This is an example of how precise verbal descriptions are so difficult."
Okay, no real argument with that. Though generally when we speak of the legs moving we aren't talking about the top end of the leg going along with the body, we are talking about the leg doing something relative to the body, specifically either catching up with the body or moving out in advance of it.