This short animated piece, which runs under 30 minutes, was produced by Reader's Digest in 1974 and features the narration of the always very lovely Richard Chamberlain. It's the most accurate adaptation of Hans Christian Andersen's story that I've seen so far, with the narration lifted almost directly from the English-translated text of the original tale, though it does gloss over the more violent details and makes the sea witch a more powerful character.
I don't know much else about this version, which I only watched recently. It covers the entire story of The Little Mermaid from beginning to end, including the epilogue, which is awesome. The feel of this animated piece is retro, bittersweet, and doesn't shy away from the spiritual nature of the story it's based on. The animation is gorgeously detailed, the kind of which we just don't get nowadays. I doubt this kind of cartoon would be made in this day and age.
Many thanks out to Autumn, who took the time to let me know about this little gem.