I. SYNONYMS: Trypanosomes, kinetoplastids, flagellated parasites.

II. NUMBER: >600 species.

III. PHYLUM CHARACTERISTICS:

• A. Structure and Physiology
  • Cell Form: Unicellular.
  • Flagella: One or two flagella that emerge from a pocket in the naked cell surface; sometimes as an undulating membrane (text with tooltip) An undulating membrane is a an upraised portion of the cell membrane that is underlain by a flagellum to form a waving fin-like structure. ; anterior flagellum tinsel (text with tooltip) A tinsel flagellum is one that is covered with flagellar hairs and thus appears thicker in light microscopy. Usually, tinsel flagella are anteriorally-directed. and posterior flagellum whiplash (text with tooltip) (1) A whiplash flagellum is a eukaryotic 9+2 flagellum with few or no flagellar hairs or scales. These may be directed anteriorly or posteriorly. (2) A whiplash flagellum is free of hair-like mastigonemes and usually is trailing or posteriorly-directed. ; anterior flagellum with a paraxial rod (text with tooltip) A paraxial rod is a stiffened rod-like structure that lies alongside the axoneme of one of the flagella in the Euglenidae. .
  • Basal Bodies: Parallel (text with tooltip) Basal bodies are parallel when their orientation relative to each other is parallel. and inserted at the base of the pocket and linked by filaments; quartet of microtubules runs alongside sides of flagellar pocket (text with tooltip) A flagellar pocket is an invagination of the cell within which the flagellar insertions occur. Extensions of the flagellar pocket form the undulating membrane in trypanosomatids. This is sometimes called the reservoir, the crypt, the cytostome (inappropriately), or gullet. and join an array of other microtubules in the pellicle (text with tooltip) A pellicle is a complex outer cellular covering that occurs within the bounds of the plasmalemma. Often synonymous with the term theca, a pellicle defines such groups as the euglenoid-kinetoplastid clade amd the Kingdom Alveolatae. .
  • Cell Covering: Covering generally naked and called a pellicle; flagellar pocket and separate cytostome (text with tooltip) Cytostome (literally cell mouth) is a permanent opening into the cell into which food particles move and are incorporated into food vacuoles. , supported by microtubules.
  • Chloroplasts: Not present.
  • Food Reserves: Not known.
  • Mitochondria: Very distinctive, single mitochondrion extends throughout most of the cell as a hoop or network with a large concentration of fibrillar DNA (k-DNA called a Kinetoplast (text with tooltip) A kinetoplast is a modified mitochondrion that is associated with the basal body (kinetosome) of kinetoplastids. Their mitochondrion had a very large amount of DNA (called k-DNA) and stains almost as a second nucleus in the cell. ) located near the basal bodies; cristae are discoid (text with tooltip) Discoid cristae (crista, sing.) are swollen tube-like cristae within certain mitochondria. . One group lacks mitochondria with a kinetoplast or cristae.
  • Golgi (text with tooltip) Golgi apparatus (also called dictyosome) is an internal membrane system of stacked flattened sacs. They occur in nearly all eukaryotes and are involved in storing and secreting cellular products. : Present and found near the basal bodies, but not connected to them.
  • Nucleus: Large, vesicular with a prominent endosome.
  • Centrioles: Absent.
  • Inclusions and Ejectile Organelles: Not known.

• B. Mitosis, Meiosis and Life History
  • Mitosis: Closed nuclear membrane with an internal spindle (text with tooltip) An intranuclear spindle elaborates within the nuclear membrane of an organism with closed mitosis. .
  • Meiosis: Not reported.
  • Sexual Reproduction and Life History: Not reported; however, parasitic species often go through complex changes in form.

• C. Ecology: Free-living and parasitic.