1. The flagellates, a subphylum of Protozoa having one or more flagella, a single vesicular nucleus, and symmetric binary fission; sexual reproduction is unknown in many groups (Volvox, Trypanosoma, Euglena). It consists of two classes: Phytomastigophorea (to which Euglena belongs), which contains chlorophyll and is therefore photosynthetic and holophytic (although this has secondarily been lost in some groups), and Zoomastigophorea (including Trypanosoma and Leishmania), which lacks chromatophores and is heterotrophic.
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