animalcule

animalcule \an-uh-MAL-kyool\, noun:

1. a minute or microscopic animal, nearly or quite invisible to the naked eye, as an infusorian or rotifer.
2. Archaic. a tiny animal, as a mouse or fly.

But man contemplates the universe as an animalcule would an elephant.
-- Edward Buwler-Lytton, Zanoni, 1842

He has absolutely no idea of the prodigious personage that I am, and of the microscopic animalcule that he is in comparison.
-- Marcel Proust, translated by D. J. Enright, In Search of Lost Time, 1989, originally published in 1927

Animalcule comes directly from the Neo-Latin word animalculum meaning "a small animal."