The image corresponds to a *circular helicoid. *It was first constructed by me in my PhD Thesis (see also this paper), and simultaneous and independently by William H. Meeks and Matthias Weber in this paper*. *The circular helicoid is a minimal surface in Euclidean 3-space generated by solving the Björling problem along a circle, with a unit normal rotating at a constant angular speed along this circle. All figures in this page are by M. Weber and can be found in his Minimal Surface Museum.