Well, the ph in nephila is a tip that its roots lie in Greek and not Latin. It might be related to Gk nephos 'cloud'. I'm not really sure. (Your best bet is to look at a scientific dictionary that lists roots used in coining new species names.) The Latin verb clavo (past particple clavatum) has a secondary meaning of 'to furnish with purple stripes'. I looked at pictures and see that it is different from the garden orb weaver we have in California.

Ceci n'est pas un seing.