Flagellat

Flagellat, commonly referred to as flagellates, designates a diverse group of mostly single-celled eukaryotes that move and feed using one or more whip-like flagella. Historically, flagellates were treated as a single phylum, Flagellata, but modern taxonomy recognizes that this is not a monophyletic group. Flagellates occur in a wide range of environments, including oceans, freshwater, soil, and animal or insect hosts. They can be free-living, photosynthetic, or parasitic, and they play important roles in nutrient cycling and food webs.

Morphology and motility: Flagella arise from basal bodies and typically rely on an axoneme with a characteristic 9+2 microtubule arrangement. Some species possess a single flagellum; others have multiple, with different flagella specialized for propulsion, steering, or feeding. In some lineages, flagella are modified or reduced, and movement can be rapid, jerky, or smooth depending on beat patterns and environmental conditions.

Reproduction and life cycles: Reproduction is often asexual through binary fission, but several flagellates also exhibit sexual processes or stage differentiation. Many form resistant cysts to survive adverse conditions, enabling persistence in fluctuating environments.

Ecology and significance: Photosynthetic flagellates (for example, some Euglena) contribute to primary production, while many heterotrophic flagellates graze bacteria. Several medically important species cause human or animal diseases, such as Giardia lamblia, Trichomonas vaginalis, Trypanosoma spp., and Leishmania spp. Flagellates are also used in research as models for studying eukaryotic evolution, metabolism, and host–pathogen interactions.

Taxonomy note: Flagellates span multiple lineages, including Euglenozoa, Diplomonada, Parabasalia, Kinetoplastea, and Heterolobosea, among others, reflecting their polyphyletic nature rather than a single coherent clade.