animalcule

noun3

1. •
   (historical) A sperm cell or spermatozoon; also, the embryo that was formerly thought to be contained inside a spermatozoon in a fully developed state.
2. •
   (no longer used) A microscopic aquatic animal, including protozoa and rotifers.
3. •
   (no longer used) A small animal.

   • Why, there is not a Man, or a Thing, now alive but has tools. The basest of created animalcules, the Spider itself, has a spinning-jenny, and warping-mill, and power-loom within its head: […] — 1831