12 Facts About Leeches

Leeches are segmented parasitic or predatory worms that comprise the subclass Hirudinea within the phylum Annelida.

Leeches were traditionally divided into two infraclasses, the Acanthobdellidea and the Euhirudinea .

Leeches show a remarkable similarity to each other in morphology, very different from typical annelids which are cylindrical with a fluid-filled space, the coelom .

Leeches are hermaphrodites, with the male reproductive organs, the testes, maturing first and the ovaries later.

Leeches either have a pharynx that they can protrude, commonly called a proboscis, or a pharynx that they cannot protrude, which in some groups is armed with jaws.

Leeches are unusual in that they do not produce certain digestive enzymes such as amylases, lipases or endopeptidases.

Leeches have between two and ten pigment spot ocelli, arranged in pairs towards the front of the body.

Leeches can detect touch, vibration, movement of nearby objects, and chemicals secreted by their hosts; freshwater leeches crawl or swim towards a potential host standing in their pond within a few seconds.

Leeches move using their longitudinal and circular muscles in a modification of the locomotion by peristalsis, self-propulsion by alternately contracting and lengthening parts of the body, seen in other annelids such as earthworms.

Leeches explore their environment with head movements and body waving.

Leeches move by looping using their front and back suckers.

Leeches can reduce swelling in the tissues and promote healing, helping in particular to restore circulation after microsurgery to reattach body parts.