The seal also looks like an Archimede Seguso piece. I haven't seen them before, so they are nice to look at. :mrgreen:
Archimede Seguso is a company named after the man. I believe that Archimede himself designed the polveri pieces. (I may be wrong, so please correct if I am.) They are also called sfummato because the colors blend into each other, with no distinct line between colors.
I do not know the value. Polveri pieces tend to sell well. If you google Seguso polveri or sfummato, you may be able to find some comparable animals in online stores.
Anita