A protist is not an animal, its a single-celled organism (not technically an organism) and can "swim" in anything
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A protist can be an animal (paramecium). A protist can be multicellular (algae) A protist is an organism because it can respond to stimuli, reproduce, develop and maintain homeostasis. They can swim in any fluid as long as it is not toxic or uninhabitable (boiling water, liquid nitrogen, sulfuric acid)) for their species.