Leech

Leeches are segmented worms in the subclass Hirudinea within the phylum Annelida.

Leeches are segmented worms in the subclass Hirudinea within the phylum Annelida. They occur in freshwater, marine, estuarine, and some terrestrial habitats, and include both parasitic species that feed on blood or bodily fluids and predatory species that eat other small animals. Leeches are found in Canadian freshwater ecosystems such as lakes, ponds, rivers, and wetlands, contributing to North American freshwater biodiversity.

Classification and anatomy

Leeches are segmented worms in the phylum Annelida, usually placed in the subclass Hirudinea or related higher-level classifications. They are distinguished by anterior and posterior suckers, reduced chaetae, and a body plan adapted for attachment and movement.

Habitat and distribution

Leeches occur on all continents and inhabit freshwater, marine, estuarine, and some terrestrial environments. Most species are associated with moist habitats, and many are especially common in freshwater ecosystems.

Feeding and behaviour

Leeches show diverse feeding strategies, including parasitism, predation, and ectocommensalism. Blood-feeding species attach to hosts such as fish, amphibians, reptiles, birds, and mammals, while predatory species feed on smaller invertebrates.

Medical use

Certain medicinal leeches have been used historically for bloodletting and continue to be used in selected modern treatments. Leech saliva contains anticoagulant compounds such as hirudin, which have biomedical applications.