Helobdella stagnalis (species of leech)
A specific species of freshwater leech. Typically encountered in biological or ecological contexts.
I found a Helobdella stagnalis leech in the pond.
Katakana spelling is common for this species name; usually written in kana.
Kanji spelling is rare; the word is usually written in kana.
Compound of 沼 (numa, 'swamp') and 蛭 (hiru, 'leech'). The exact derivation is straightforward.