Dogora: The Space Monster (1964)

Authorities are puzzled when diamonds begin disappearing, but the real shocker is the thief's identity: a giant alien jellyfish! The world spins into chaos as gems go missing from Tokyo to New York City, and scientists learn that an alien is sucking up the Earth's matter, ingesting it and multiplying. As the sky becomes filled with hungry jellyfish, it's up to officials to save humankind from extermination.