I was once told that the difference between a carousel and a
merry-go-round is that a carousel is all horses and it came from the
device that was used to train knights for jousting.  A merry-go-round
has other animals.  I don't think this is true, though, as I have seen
many rides labeled as one fit the description of the other.

All American rides go in the counter-clockwise direction.  The right
side of the horses and animals are usually more ornately carved than
the left side.  Some English rides go clockwise.  I have seen some
evidence that "merry-go-round" is an English term, so that might be
where the direction/name association came from, though the term is
pretty much interchangeable in the carnival industry today.

Todd Robbins