I wonder why there are only six. Usually if you go outside of the three explicitly mentioned in the Bible (Gabriel, Michael, and Raphael) you have seven. Firstly because seven is one of those symbolic numbers in the Bible, representing completeness and a type of spiritual perfection.
And secondly, in the deuterocannonical book of Tobit, the archangel Raphael explicitly says, "I am Raphael, one of the seven holy angels, who present the prayers of the saints, and who go in and out before the glory of the Holy One." (Tobit 12:15). The other names (at least in Catholicism) are considered speculative, and aren't considered to be canon (I believe). Uriel comes from the Book of Enoch, but pretty much no one considers that canon except for the Ethiopian Orthodox Tewahedo Church. Apparently some Coptic Orthodox say there are 8, though I don't really know how they get that.
I guess is it supposed to be Lucifer, right before he's kicked out of their number? Otherwise I have no earthly idea why you'd only have six of them.