Man From Atlantis aired on NBC as a series of 4 television movies during 1976-1977 before getting the green light for a 13 episode run in 1977. It starred a young Patrick Duffy as an amnesiac who is believed to be the sole surviving citizen of the lost fabled city of Atlantis. He is given the name Mark Harris by his rescuers, Dr. Elizabeth Merril (Belinda J. Montgomery) and C.W. Crawford Jr. (Alan Fudge) who are employed by the Foundation For Oceanic Research. Mark is obviously different as he has webbed hands, gills, and a sensitivity to light. He is recruited by the Foundation and travels upon the submarine, the Cetacean, getting into all sorts of adventures.
The main villain of the series would probably be the Wild Wild West alumni, Victory Buono, as Mr. Schubert.
Man From Atlantis also had a comic book series from Marvel Comics, the issue posted below was one of the first comics I picked up in my youth.
A big thanks goes to Condorman76 over on Flickr for the publicity shot at the top of this post!