Ascaris lumbricoides

Etymology
Ascaris lumbricoides:

ascaris: "intestinal worm" (from Greek ἀσκαρίς (askaris), meaning "intestinal worm"undefined)

lumbricoides: "worm" (from Latin lumbrīcus, meaning "worm"undefined)

Explanation
Ascaris lumbricoides is a worm (lumbricoides), specifically a nematode, which can infect humans and lives in the small intestine (ascaris)undefined.