There is some discussion about which ten species served as the initial members of the UFP. It is known that Human, Vulcan, Andorian, and Tellarite representatives were the first four founding members to support the initiative. There are at least three other species that were awarded entry very soon after, but the name of their homeworlds escape me. The Gideon may be one of them, and the Caitian too. Klingons are not members of the UFP, but the Empire did sign a treaty in the 2240's after the Enterprise C sacrificed itself to defend a Klingon post. Romulans have not been depicted as members of the UFP, but the coming Star Trek Online may lead to new developments on that frontier. According to Memory-Alpha, the Denobulans and the Rigelians may also be secondary members, signing on soon after the founding.