Twelve men with this high calling constitute an administrative council in the work of the ministry. When a vacancy occurred with the death of Judas Iscariot, Matthias was divinely appointed to that special office as a member of the council (Acts 1: 15-26). Today twelve men with this same divine calling and ordination constitute the Quorum of the Twelve Apostles in The Church of Jesus Christ of Latter-day Saints.
The title was also applied to others who, though not of the number of the original twelve, yet were called to serve as special witnesses of the Lord. Paul repeatedly spoke of himself as an apostle (Rom. 1: 1; 1 Cor. 1: 1; 1 Cor. 9: 1; Gal. 1: 1). He applied the titles to James, the Lords brother (Gal. 1: 19), and also to Barnabas (1 Cor. 9: 5-6; cf. Acts 14: 4, 14). The New Testament does not inform us whether these three brethren also served in the council of the Twelve as vacancies occurred therein, or whether they were apostles strictly in the sense of being special witnesses for the Lord Jesus Christ.
Jesus is referred to as an apostle in Heb. 3: 1-2, a designation meaning that he is the personal and select representative of the Father.
In Luke Chaper ten we learn that Christ sent out seventy, two by two, in addition to the Twelve that were His disciples. In other ancient texts and early Christian writers we learn that the seventy witnesses were also preserved after the resurrection as part of the organization of the church.
We as LDS are familiar with such a calling. "Seventy" to us is an ancient calling found first in the Melchizedek Priesthood of the Old Testament. Then as now, they were sent to judge Israel or in other words to preach. We also have a First Quorum of Seventy today that are given the primary task to declare the Word of God.
That Paul was subject to the Twelve is evident in Acts 15 when he appealed to the Twelve for authority on the matter of circumcision. Paul though an apostle at this time, did subjugate himself to the authority of the Twelve. Paul was given Barnabas, by the Twelve, and was sent by them to the areas that they were to preach. All of these evidences indicate that Paul while an apostle was not, at least at these times, one of the Twelve Apostles.