There is no such thing as a living organsim that is more "primitive" than
Drosophila and more "advanced" than C. elegans.
If you want to use a mammalian gene to clone a C. elegan homolog then
you might as well screen the C. elegans library directly. There are
no evolutionary intermediates that will help you.
Modern living species cannot be arranged on a evolutionary ladder from
primitive to advanced. This is a false notion of evolution that was
discredited more than one hundred years ago.