'draw'-Gnuplot interface:
object spherical

Once you have opened a Maxima session, load package draw:

load("draw") $

To read the documentation on object spherical, write the following sentence:

describe(spherical) $

Function defined in spherical coordinates. In this example, variable a is the azimuth and variable z is the zenith. The expression is for the radius:

draw3d(
  surface_hide = true,
  axis_3d      = false,
  color        = salmon,
  spherical(sin(z)*cos(2*a),a,0,2*%pi,z,0,%pi))$

A geometrical model for genus Nautilus:

draw3d(
  color        = green,
  surface_hide = true,
  axis_3d      = false,
  spherical(a+z,a,0,3*%pi,z,0,%pi))$

'draw'-Gnuplot interface:object spherical