Terran leech
From Memory Alpha, the free Star Trek reference
The Terran leech is a leech native to Earth. It consumes hemoglobin present in the blood of many other Earth organisms. (TNG: "Phantasms")
Leeches were used as part of primitive medicine on Earth, and are often referred to when disparaging apparently outdated medical techniques. In 2374, the EMH Mark II aboard the USS Prometheus remarked to the Doctor that medical science had evolved beyond "scalpels or leeches" when the latter failed to recognize a thrombic modulator. (VOY: "Message in a Bottle")
