Leech

Mainly freshwater environments like ponds, lakes, and slow-moving streams; some are terrestrial or marine.

Hematophagous (blood-sucking) on vertebrates or carnivorous/scavenging on small invertebrates.

Hermaphroditic reproduction; move using anterior and posterior suckers in a looping motion or by swimming.

Risks include potential localized infection or allergic reactions from bites. Benefits include ecological roles as prey/predators and historical/modern medical use for bloodletting and microsurgery recovery.