new marker: how to make a spiral

Hi

I am using "verts" in the matplotlib scatter function and managed to
create many new symbols for scatter plots. One I cannot make is a
spiral-like symbol (logarithmic spiral) because it does connect the
first and last point of the verts series of x,y points I am defining. Is
there a way to avoid that? (so that the spiral-curve stays "open")

thanks!

Eric