rotifer
A microscopic aquatic animal of the phylum Rotifera. In Japanese, usually written in katakana as ワムシ.
When I looked at the pond water under a microscope, many rotifers were swimming.
Common katakana spelling for this organism name.
Kanji spelling is rare; the word is usually written in kana.
From 輪 (wa, 'ring') + 虫 (mushi, 'insect, worm'), referring to the wheel-like corona of cilia. The exact historical derivation is uncertain.