Most microorganisms are unicellular -LRB- single-celled -RRB- , but this is not universal , since some multicellular organisms are microscopic , while some unicellular protists and bacteria , like Thiomargarita namibiensis , are macroscopic and visible to the naked eye .

Micro-organisms are often described as single-celled , or unicellular organisms , but there are unicellular protists that are visible to the human eye , and some multicellular species are microscopic .
