When it comes to obscure Ecco media you probably can't go much more than the version that was made for the Sega PICO console meant for very little children. The system was positioned as an edutainment computer and would help teach them simple math, basic shapes, music and so on. Suffice it to say, the whole concept was very much ahead of its time for 1993, incorporating a "Magic Pen" stylus that would work very much like modern day Wacom tablets as well as "Storyware" cartridges that were made like little books where you can control what happens on the TV screen by flipping its pages and using the Magic Pen to interact with them!
The sound chip inside PICO is the SN76489, the same one used in Master System and Game Gear, which was an overall downgrade in versatility. That did not stop Attila Héger from composing a beautiful soundtrack for this game and having finally gotten my hands onto an actual console as well as Ecco Storyware for it I was able to establish how the music is supposed to sound and hack the subroutine responsible for playing the tracks to extract them as they're meant to be played.
We are hereby happy to give you the complete soundtrack of
Ecco Jr. and the Great Ocean Treasure Hunt!, including every Ecco fan's favourite theme that's used here in transition scenes 
You can right-click the player to download the files.
- Triumphant Fanfare
- The Whale's Underwater Home
- Ruins Beneath The Sea
- Creatures of The Ocean Floor
- Denizens of The Deep
- Transition Scene