Animals are organisms that have ingestive metabolism. Protozoans - protists that ingest food by endocytosis. Most protists are aquatic. Some live in marine environments, others in fresh water, and others in body fluids of other organisms. Endosymbiosis - organisms living together, one inside the other.
Slime molds live in damp soil and the moist, decaying bark of rotting trees.
Organelles Contractile vacuole - a membrane enclosed vesicle that removes excess water. Food vacuole - a membrane enclosed vesicle where engulfed food is digested. A few protists are surrounded by a plasma membrane. Protozoans have internal shells that they produce. Many algae and other protists have cell walls.