Modifiers matching protoctist:

• microscopic,
• unicellular,

Simple categories matching unicellular:

• microbe,
• anaerobe,
• parasite,
• organism,
• microorganism,
• pathogen,
• plankton,
• animal,
• plant,
• algae,
• eukaryote,
• being,
• phytoplankton,
• protoctist,
• form,
• protist,
• chlorophyte,
• creature,
• system,