aflagellate

An aflagellate is an organism or cell that lacks flagella, the slender whip-like appendages used by many bacteria, algae, protists, and some animals for locomotion. The term is used for cases where flagella are absent either permanently, as a characteristic of the lineage, or temporarily, such as during certain life stages or developmental states. In bacteria and archaea, aflagellate taxa either have lost flagella through evolution or never possessed them. In eukaryotes, flagella and cilia are structurally related, and many protists are flagellated; aflagellate species occur among Amoebozoa and other groups, often relying on amoeboid movement or gliding for locomotion. In fungi and many plants, most cells and life stages are aflagellate; some early-diverging fungi (chytrids) retain flagellated spores, illustrating that flagella can be present in particular life stages or lineages.

Aflagellate organisms can still move or feed by alternative mechanisms, such as pseudopodia, cytoplasmic streaming, or slime gliding. Flagella also serve sensory roles; their absence may reflect ecological adaptation or energetic trade-offs. The term is primarily used in microbiology, protistology, and cytology to describe the lack of flagella in a given organism or cell type, contrasting with flagellate forms. Modern taxonomy increasingly emphasizes molecular data, but aflagellate status remains a straightforward functional trait with implications for ecology and evolution.