This is a nudibranch or sea slug, sometimes called a Spanish Dancer, native to the waters of Indonesia. They are sometimes called sea butterflies, but their bright colors actually mark them as poisonous and bad-tasting to hungry sea creatures looking for a snack. And that’s a good thing since this one gets stuck for a brief moment.
This National Geographic link has some excellent nudibranch photos. And for a previous video study in locomotion, check out the Ribbon Eel.