To which goddess does Claudio compare Hero? What is the significance of the comparison?

He declares she is like Diana, goddess of the virgins. Of course Claudio will come to believe that Hero isn't so virginal after all. This of course is the thing with Shakespeare's men. They see their love interests as either virginal and pure or the opposite. All it takes is rumour and innuendo to make the jump from thinking their woman to be virginal and "pure" to hoar.

Claudio tells Hero that she is like the goddess Diana on the outside (publically), but when they're alone she seems more like Venus (the goddess of sexuality).