'animalculae' originates from New Latin, specifically the word 'animalculum,' where '-culum' meant 'a diminutive (little)' and 'animal' meant 'living being'.

'animalculum' transformed into the English word 'animalcule,' and eventually the learned plural 'animalculae' entered English via scientific and Neo-Latin usage.

Initially, it meant 'little animals,' but over time it evolved into the historical/scientific sense of 'microscopic organisms' and is now archaic in general usage.