Polo necks, turtlenecks, and everything in-between

I had an interesting conversation at work the other day regarding the terminology for certain items of winter clothing - specifically those tops that have extended necks. In the US, we would call them "turtlenecks." If the neck was only 2" high, though, we would term it a "mock turtleneck." I was told that here, however, a turtleneck is a "polo neck," and a mock turtleneck is simply a turtleneck (because it looks like a little turtle sticking his neck out). I went along with this theory, and then a few days later came back with this question - if a polo neck is a turtleneck, what do you call a polo shirt?! The answer is a tennis shirt - but only posh tossers wear them, so no one ever talks about them.