The following is a list of unnamed Arcadians.
Ambassador
Arcadian ambassador in 2285
This ambassador served as a representative on the Federation Council in 2285 and witnessed the trial of Admiral James T. Kirk. (Star Trek IV: The Voyage Home)
The Arcadian ambassador was played by an unknown performer.
Councilors
Two Arcadian councilors
Two councilors were present at Starfleet Headquarters in 2285 around the time of the trial of Admiral James T. Kirk. (Star Trek IV: The Voyage Home)
One of these is presumably the ambassador above; both were played by unknown performers.
Councilors
Two Arcadian councilors
Two councilors were present at Starfleet Headquarters in 2364 when the USS Enterprise-D returned to Earth to investigate a conspiracy. (TNG: "Conspiracy")
This scene is re-used footage from Star Trek IV: The Voyage Home.