It has confused with "Hirudo medicinalis", but has recently been recognized as different species. The medicinal leech, "Hirudo medicinalis," and sea slug are classic model systems for studying nociception. There is "Hirudo medicinalis" and "Lymnaea" in the stream. The most well-known leech species, "Hirudo medicinalis" (European Medical Leech), belongs to the Arhynchobdellida. Hirudo medicinalis is used in TCM to treat amenorrhea, abdominal and chest pain, and constipation.