I. SYNONYMS: Sarcodina, amoebae, rhizopods, Lobosa, Tubulinea.

II. NUMBER: > 900 species.

III. PHYLUM CHARACTERISTICS:

• A. Structure
  • Cell Form: Mostly uninucleate amoebae with lobose (text with tooltip) Lobose (adj.) usually refers to the rounded shape of certain pseudopods. pseudopodia.
  • Flagella: Present in some, particularly the pelobionts in which the flagella are anteriorly-directed (text with tooltip) An anteriorly-directed flagellum extends in the direction of the motion of the motile cell. The interpretation is that the flagellum functions by pulling the cell. .
  • Basal Bodies (text with tooltip) Basal bodies (also called kinetosomes) are organelles that are not membrane-bound. All eukaryotic flagella (also called undulipodia) are underlain or attached to the cell by the basal body. The basal body is a microtubular structure with the general formula 9(3)+0. They are indistinguishable from centrioles. : Present in some, but not paired.
  • Cell Covering: Naked amoebae; some with tests (text with tooltip) A test is an external covering that is secreted or constructed by secretions from the cell. I distinguish it from a cell wall in that a test is not appressed to the plasmalemma. In fact, sometimes the cell can leave the test entirely ; some produce cysts (text with tooltip) A cyst is a resting stage that is covered by a resistant outer covering. Usually, cysts are able to allow the cell to survive environmental extremes. They serve as the infective forms of parasitic protists. Usually in sexual microbial eukaryotic groups, the cyst is produced by the zygote. .
  • Chloroplasts: Not present, but some have photosynthetic endosymbionts.
  • Food Reserves: Not known.
  • Mitochondria: Present with tubular cristae (text with tooltip) Mitochondrial cristae that form as extended saccate structures or tubes are called tubular cristae. . Some taxa are amitochondriate, but presumably have lost their mitochondria.
  • 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. : Probably present.
  • Nucleus: Some with organized chromosomes; most contain endosomes.
  • Centrioles: Not present.
  • Inclusions and Ejectile Organelles:
  • Food vacuoles: contractile vacuoles; gas vacuoles in testate forms.

• B. Mitosis, Meiosis and Life History:
  • Mitosis: Closed (text with tooltip) Mitosis is closed when the segregation of daughter chromosomes occurs within the bounds of the nuclear membrane (the nuclear membrane does not break down). with internal spindle (text with tooltip) An intranuclear spindle elaborates within the nuclear membrane of an organism with closed mitosis. . There are 3 types: Promitotic (text with tooltip) Promitotic (adj.) mitosis occurs in closed mitotic systems with an intrnuclear spindle and a persistent nucleolus. (intranuclear spindle with a persistent nucleolus), Mesomitotic (text with tooltip) Mesomitotic (adj.) mitosis occurs in open mitotic systems with delayed breakdown of the nuclear envelope and no persistent nucleolus. No centrioles. (delayed breakdown of the nuclear envelope and nucleolus, no centrioles), Metamitotic (text with tooltip) Metamitotic (adj.) mitosis occurs in open mitotic systems with breakdown of the nuclear envelope and nucleolus. No centrioles. (breakdown of the nuclear envelope and nucleoli, still no centrioles).
  • Meiosis: Probably not present; however, Pneumocystis has been reported to have meiosis.
  • Sexual Reproduction and Life History: Probably not present; however, there was a questionable report of motile gametes in Trichosphaerium. Many other members of this phylum produce resting cysts (or infective cysts for parasitic forms).

• C. Ecology: Free-living to parasitic.