Hirudidae

Hirudidae is a family of annelid worms known as leeches. Members are primarily aquatic, with most species living in freshwater, though some are terrestrial or semi-aquatic. They occur worldwide in temperate and tropical regions and range from a few millimeters to several centimeters in length.

Anatomy and physiology: Like other leeches, hirudids are dorsoventrally flattened and segmented into a series of annuli. They possess an anterior and a larger posterior sucker used for feeding and locomotion. They lack chaetae (bristles) and parapodia. The digestive system is adapted for blood feeding in many species, with specialized salivary glands that secrete anticoagulants such as hirudin, aiding the meal.

Ecology and behavior: Most hirudids are temporary ectoparasites that attach to vertebrate hosts, obtain a blood meal, and detach. Some species are predatory on invertebrates or scavengers. Reproduction usually involves hermaphroditism with cross-fertilization; they produce a cocoon-like egg case laid in moist environments.

Taxonomy and nomenclature: The name Hirudidae appears in older or alternate taxonomic treatments; in many modern systems the leeches are placed in the family Hirudinidae. Taxonomic placement has varied as new phylogenetic studies refine annelid relationships.

Medical significance: The saliva of many leeches contains anticoagulants, vasodilators, and anesthetics. The medicinal leech Hirudo medicinalis has a long history of use in medicine and continues to play a role in modern micro-surgery and reconstructive therapies.