Species is a taxanomical classification consisting of organisms which should be able to interbreed and produce fertile offspring.
Refering to some of the species in the genera, but not necessarily all (usually, if you want to mention all you stop at the genera), you'd use spp.
Refers to a single species in the genera you'd use sp.
After all this you might add descriptives such as common name or original location for clues or clarity. Don't know if this is sanctioned by the ICZN and ICN but it works.
So
Avicularia sp. Peru basically means It's an Avic, don't know which species but it comes from Peru hehe!
Oh and I had it wrong. Only the General and species should be italics, the sp or spp should not. :S