The equator is the only parallel of latitude that's a great circle.
In fact, it's the only locus of any constant coordinate that's a great circle,
since the meridians of longitude are all semi-circles.
The Equator
The name for 66.5 degrees south latitude is the Antarctic Circle.
The line of latitude that runs through the north of Iceland is the Arctic Circle, which is at approximately 66.5 degrees north latitude.
The Arctic Circle
66.5 degrees north latitude is commonly referred to as the Arctic Circle.
The Antarctic Circle is the major circle of latitude that follows the Tropic of Capricorn.
The name for the line of latitude is the Equator (the most important line of latitude).Others include:North PoleSouth PoleArctic CircleAntarctic Circle
The Antarctic Circle
difference circle
You are probably thinking of the arctic circle, which is at about 66 degrees north latitude.
You may be referring to the Antarctic Circle, at 66.5 degrees south.
That is the approximate latitude of the Arctic Circle, which is the set of southernmost points north of which there is no sunrise on the winter solstice and no sunset on the summer solstice.