This hook also appears as a Recurring Riff in the 'Snowman's Land' music in Super Mario 64.
The underwater theme is very similar to the Waltz 5B section of Johann Strauss's 'Blue Danube', and to a lesser extent Tchaikovsky's 'Waltz of the Flowers' from The Nutcracker.The first six notes of the original theme is actually suspiciously similar to the Minsky Pickup.