Riemann surface

This deformed, self-intersecting disc is called a “Riemann surface”, named after Bernhard Riemann who first studied these complex one-dimensional surfaces. Essentially, a Riemann surface is a deformed one-dimensional plane, usually a disc, which has been twisted or contorted to intersect, forming all sorts of shapes.

This model was designed by Gabriel Ignat (Bodleian Libraries) based on a model by Leonid 2 (Wikimedia Commons).