Kingdom comprising organisms with a relatively simple organization that are regarded as intermediate between or distinct from animals and plants, especially unicellular eukaryotes. They may share certain morphological and physiological characteristics with animals or plants, or both. They may be either free-living or gathered into simple colonies, and having diverse ways of nutrition and reproduction.原生界包含的有機體構造簡單，被視為是介於動物與植物之間，或與動植物不同的生物，多為單細胞真核生物。它們在形態上與生理上，可能與動植物擁有某些相同的特徵；可獨立生存，也可能形成小型集群，且攝取養分與繁殖的方式多樣。