[Nymph Philosophy] Why the nude female form?

[Pythagoras]

I interpret it as an antiquarian metamyth where the virgin nymphs represent nature/mother-nature.
We talk about virgin forests, so i think its also possible that they are symbolic of forests, and so they are linked by the waterways.
These water nymphs were present in ancient Greek myths and pagan and celtic myths of Europe.
The mother nature myth being prevalent across all the world before more masculine religions replaced them.

Its also possible they represent ghosts of the underworld as a portrayal of the myth of Persophene and her decent into the underworld.