Which organisms have prokaryotic cells?

Prokaryotic cells are found in organisms belonging to two of the three domains of life: Bacteria and Archaea.12

These organisms are defined by their simple cellular structure, which lacks a membrane-bound nucleus and specialized intracellular organelles. While Bacteria and Archaea are both prokaryotic and share certain superficial similarities—such as the absence of organelles and the presence of circular DNA—they are fundamentally distinct groups with separate evolutionary lineages.12

Historically, all prokaryotes were grouped together, often under the kingdom Monera, but modern classification systems based on genetic and molecular evidence now recognize them as two separate domains. Members of these domains are highly diverse and can be found in a wide range of environments, from common habitats to extreme conditions like hydrothermal vents or highly acidic soils.132