1) A very heterogeneous group (35 phyla!); include some important parasites of humans: malaria, sleeping sickness, beaver fever
2) Actual phylogenetic relations & classification hotly debated; four 'groupings of convenience' based mainly on locomotion:
a) Flagellates- use one or more flagella; includes both phytoflagellates (have chloroplasts*) and zooflagellates (lack chloroplasts)
EXAMPLES: dinoflagellates*, Euglena*, Volvox (colonial)*, diatoms*, choanoflagellates, Trypanosoma, Giardia
b) Sarcodines- use pseudopodia (lobe- or spine-like outgrowths) of ectoplasm; some produce spectacular skeletons
EXAMPLES: amoebas, slime molds, foramenifera, radiolarians
c) Sporozoans- most move by body flexion (some use flagella or pseudopods); all are parasitic
EXAMPLES: Plasmodium (malarial parasite)
d) Ciliates- use cilia; includes the most structurally complex protozoans that come in a remarkable variety of forms
EXAMPLES: Paramecium, Stentor
3) Defining characters: a) unicellular (some colonial); b) eukaryote (distinct nucleus & membrane-bound organelles);