中美洲

原生動物(protozoan)

任何微小的（常常在顯微鏡下才能觀察到的）單細胞原生生物。它們在大多數土壤、乾淨的水和海洋中都可見到。大多數是單獨存在的個體，但也有不同的群居物種。原生動物之間以及原生動物和原生生物之間在分類學上的關係時常被改動。最小的已知原生動物是小於2微米的小型血液寄生蟲，而最大的則可能有16釐米長，能被肉眼看見。原生動物在形態變化上有差別，但都有一些共同的真核生物特點，如都有油性蛋白質的膜和帶膜的液泡及細胞器官（參閱eucaryote）。它們在活動方式、營養和生殖上的差別很大。在原生動物的分類上存在不同的分類系統。主要的門包括肉鞭門（帶鞭毛的和帶延展細胞質，即偽足）、纖毛門（帶纖毛的）、頂覆門、微孢子門和黏體動物門（能產生孢子的）。頂覆門和微孢子門常常被包括在簡單的孢子亞門中。常見的原生動物包括腰鞭毛蟲、阿米巴和草履蟲（參閱Paramecium）。

English version：

protozoan

Any of a group of small (usually microscopic) single-celled protists. They are found worldwide in most soils,fresh water,and oceans. While most are solitary individuals,various colonial forms exist. The taxonomic relationships of protozoans to one another and to other protists continue to be revised. The smallest known protozoans are tiny blood parasites less than 2 microns long; the largest may be 16 mm long and visible to the naked eye. Protozoan shapes vary,but all share such eukaryotic features as lipid-protein membranes and membrane-enclosed vacuoles and organelles (see eukaryote). They show wide variation in modes of movement,nutrition,and reproduction. Various classification systems exist to group the protozoans. The major phyla include Sarcomastigophora (flagellated forms and forms possessing cytoplasmic extensions called pseudopodia),Ciliophora (ciliated forms),and Apicomplexa,Microspora,and Myxozoa (spore-producing forms). Apicomplexa and Microspora are sometimes included in the single phylum Sporozoa. Commonly known protozoans include dinoflagellates,amoebas,and paramecia (see paramecium).