implicitplot3d equivalent in Maxima?



I've been using Maxima for a while, and find it very useful, and a great
alternative to Maple.  However, there is one feature that I use a lot in
Maple that I haven't been able to find in Maxima: implicitplot3d.  I notice
that there is a 2d implicit plot, but nothing for 3d.

 

Does anybody have any recommendations on how to plot something like
y=x^2/2+z^2/4 in Maxima?

 

Thanks

 

Mike Williams