Mastigophora

Subphylum of protozoa typified by the possession of one or more flagella (whiplike organs).

Classification Mastigophora is a subphylum in phylum Sarcomastigophora.

The group is composed of two classes, the Phytomastigophora and the Zoomastigophora. The Phytomastigophora have chlorophyll and are free-living in the sea, fresh water, and soil. They include Euglena and Volvox. Possessing chlorophyll, they are able to synthesize organic compounds from inorganic ones using the energy of sunlight; some, however, are colourless, and thus require organic matter to survive. This difference occurs within the members of one genus, Euglena, and illustrates the difficulties of deciding whether they are plants or animals.

Members of the Zoomastigophora have no chlorophyll and require organic food particles. Some species, such as Peranema, obtain these by engulfing large living prey such as Euglena. Members of the order Choanoflagellida are filter feeders. They are sessile (fixed) and feed by setting up a current with the flagellum. This current is drawn through the collar, which encloses the base of their flagellum. Here any particles are filtered off and move down through the base of the collar to form food vacuoles. Some Zoomastigophora are parasitic and cause economically important diseases such as leishmaniasis, malaria and trypanosomiasis (sleeping sickness).

Many species of Phytomastigophora have chalky, siliceous, or cellulose coverings which may be divided into plates. In one order (the dinoflagellates, such as Noctiluca and Ceratium) these plates are of cellulose and provide grooves in which lie the flagella. The plates may have spines or processes giving very distinctive shapes to the organisms.

Reproduction This is usually by fission along the long axis to give mirror-image daughter cells. The armoured dinoflagellates divide obliquely, and may either split the envelope between the daughter cells, or the old envelope may be discarded altogether. The situation is more complex in colonial forms such as Volvox. The normal form is that of a hollow sphere, the flagella directed outwards, with each individual contained in a cellulose envelope connected to the next one. Locomotion is achieved by coordinated beating of all the flagella. Many hundreds of individuals may form one of these colonies and reproduction is by fission of cells near the lower pole, resulting in a sphere of daughter cells within the parent colony. The flagella of the daughter colony are directed to the centre of the sphere initially, and the sphere everts before the new colony escapes through a rupture in the parent colony.