What is the fundamental requirement for an organism to be classified within Kingdom Animalia?

Being a multicellular, eukaryotic organism that must consume organic material

Kingdom Animalia represents one of the broadest classifications in the Linnaean system, encompassing nearly all organisms commonly recognized as animals. The fundamental criteria for inclusion are being multicellular and eukaryotic. Furthermore, members of Animalia are heterotrophs, meaning they must actively consume pre-existing organic material for energy, rather than producing their own food like plants. They also share essential characteristics such as the ability to move (though this varies greatly) and the necessity to breathe oxygen and reproduce sexually. The Yorkie shares this basic biological blueprint with everything from blue whales to microscopic invertebrates.