Ariel and Flounder find a human instrument that Ariel, naturally, wants to play. It's a harp, but she calls it a Stringamajigger, and she's pretty good at it. This amused me way more than it should have, because the harp music does typically imitate the soothing sounds of the ocean, so it makes sense that a mermaid would be able to play it well.
However, Triton rains on Ariel’s parade when he gives her a Sea Calliope, an Atlantican musical instrument that he wants Ariel to learn to play. Turns out that Triton has fond memories of his Grandfather Neptune playing the Sea Calliope, and since no one else in the family learnt to play it, I guess he figured his talented youngest daughter would be the best choice to take up lessons. Sebastian is charged to be her teacher. Ariel doesn't have the heart to say no to her father when it obviously means so much to him.
Unfortunately, Ariel has no talent in playing the Sea Calliope. She's awful at it, and to make things worse, her playing wakes up the Ancient Seaclops, a creature that is supposed to sleep for a thousand years, and he's pretty cranky at being woken up early. Years earlier, the Seaclops had destroyed Neptune's Calliope, and he's pretty miffed that there's a new one in Atlantica.
King Triton, in his premature joy, arranged a recital for Ariel. That turns out to be the last straw, and the Seaclops attacks.
- The Ancient Seaclops later returns in Issue 3 of Marvel Comics' The Little Mermaid series: "The Daredevilfish", where he clearly wanted revenge for being woken up.