Order amidst animalcules: the Protoctista kingdom and its undulipodiated cells

The eukaryotic microorganisms have always been studied and described in the context of Zoology (as tiny animals), Botany (as tiny plants), Mycology (as water molds) or Microbiology (as disease agents). Because their extent (as a group of about 200,000 species) and differences from the rest of life (worthy of Protoctista kingdom status) only recently has been recognized, their classification within the Plant and Animal kingdoms remains in scandalous disarray. Admitting this problem, this paper represents a step toward achieving nomenclatural order based on ultrastructural, biochemical and evolutionary considerations.