Many eukaryotes have long slender motile cytoplasmic projections, called flagella, or similar structures called cilia. Coccolithophores are minute unicellular photosynthetic protists with two flagella for locomotion. Microtubules have a major structural role in eukaryotic cilia and flagella. Common mechanisms of motion include flagella and cilia. In other words, sperm cell flagella and Fallopian tube cilia are "homologous" structures. An amastigote is a protist cell that does not have visible external flagella or cilia. Axonemes are the elongated structures that make up cilia and flagella. Most oomycetes produce self-motile zoospores with two flagella. A number of terms related to flagella or cilia are used to characterize eukaryotes. Cilia are short and more numerous than flagella. Protozoa are largely defined by their method of locomotion, including flagella, cilia, and pseudopodia. These cells are motile by means of a monopolar polytrichous flagella. The species are motile with amphitrichous flagella and rarely nonmotile. They also make up the internal structure of cilia and flagella. It is heterotrophic, oxidase-positive, and motile by means of a single polar flagella.