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The one-celled non-photosynthetic eucaryotes (Protozoa) are
probably the group from which all other eucaryotes evolved. They possess
a diversity of locomotor adaptations: pseudopods for amoeboid locomotion,
flagellae, and cilia. Some are non-motile. Locomotor adaptations distinguish the various types of Protozoa:
Phylum Mastigophora (Flagellata): Flagellated unicells that move by beating a long, whip-like flagella with a "9 + 2" grouping of microtubules. Some species show both flagellar and amoeboid locomotion, giving evience that the Mastigophora and Sarcodina are related. Apicomplexa (Sporozoa): A group of nonmotile unicells, including the malarial parasite Plasmodium. Because the Sporozoa reproduce by spores, they may be close to the ancestry of slime molds and fungi. Phylum Ciliata (Ciliophora): Cells covered with hairlike cilia organized into a continuous layer or pellicle. Beating of the cilia controls both locomotion and feeding. The plasma forms a food vacuole by budding inward, a process similar to phagocytosis. The Ciliata are unusual in having two nuclei in each cell, which makes for a very complex process of sexual congugation, so different from other Protozoa that that many biologists believe that the Ciliata evolved independently. Paramecium is a commonly studied ciliate. Plant-like protists: Pyrrhophyta, Chrysophyta, and certain other photosynthesizers are sometimes called alga-like Protista, but they all possess plastids and plant-like pigments, and so are often treated as algae. |
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