Astro Boy 1963 Season 3 Episode 23 Dolphins in Distress

Mr. Hall is building an undersea city to boost tourism. Seemingly out of nowhere, crab-shaped robots and vehicles in the shape of porpoises attack the city. A message left behind by one of the porpoise vehicles says that they are descendants of porpoises belonging to the Dolphin tribe, and they want to halt construction of the undersea city as it's endangering their existence. After receiving the message, an angry Mr. Hall captures Prince Pip of the Dolphin tribe.