This happens on a lot of names. Sometimes it represents different branches of the same family. But often it can be the reference to the entire family--the Ricciardi--like the Smiths, rather then the individual Ricciardi family, like Smith.
I have seen over time in the Italian records the name ending change over time. Just bear in mind you need to look at both spellings when reseaching. If you go back in time and find the earliest records, you might determine what is the oldest spelling of the surname.