This is an unusual sequence in that it's cast by animator. Woolie Reitherman handles all three main characters in this sequence: Pinocchio, Jiminy and Monstro. His Pinocchio has a much longer nose than usual. His Jiminy has a smaller head than Ward Kimball draws for the character.
Reitherman was known as an action animator and that's certainly how he's cast here. The action is frantic on the part of all the characters.
The sense of scale and power are preserved by Monstro's relationship to the tuna and the destruction of the underwater arch.
Mention must be made of John McManus's tuna animation. The tuna are not characters but they're believable fish and they're animated in ways that don't confuse the eye. I assume that Cornett Wood did most of the bubble and airbrush streak work, two things that add to the richness of the scene. I also assume that Sandy Strother is responsible for the fracturing rock archway in shot 3, which is very effective.
Jiminy's cowardice, swimming ahead of Pinocchio in order to save himself, leads to him being locked out of Monstro and much of the climactic action. As always in this film, doing something to help others leads to positive results and doing something selfishly leads to trouble. However, just as it was necessary for Pinocchio to go after Geppetto without Jiminy's prompting, it's necessary for Pinocchio to save Geppetto without Jiminy's help. While Jiminy's actions fit with the worldview of the film, they are also a script convenience to get him out of the way.