Rhynchobdellida (from the Greek ''rhynchos'', mouth, and ''bdellein'', sucking), the jawless leeches or freshwater leeches, are an order of aquatic

leeches Leeches are segmented parasitic or predatory worms that comprise the subclass Hirudinea within the phylum Annelida. They are closely related to the oligochaetes, which include the earthworm, and like them have soft, muscular segmented bo ...

. Despite the common name "freshwater leeches", species are found in both sea and fresh water. They are defined by the presence of a protrusible

proboscis A proboscis () is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In invertebrates, the term usually refers to tubular mouthparts used for feeding and sucking. In vertebrates, a proboscis is an elong ...

instead of jaws, and having colourless blood. They move by "inchworming" and are found worldwide. The order contains 110 species, divided into 41 genera and three families. Members of the order range widely in length, usually between 7 and 40 mm. They are hermaphrodite. The order is not monophyletic.

Appearance and eating habits

Smooth Turtle Leech imported from iNaturalist photo 3860130 on 27 November 2022

Instead of jaws and teeth, Rhynchobdellidae have protrusible proboscises, which they use to penetrate the host's skin. Mouths of Rhynchobdellidae species are small holes from which the proboscis can be protruded. The proboscis then sucks out the desired bodily fluid from the host: usually blood or coelomic fluid in the case of invertebrate victims. Rhynchobdellidae are either sanguivorous or

predatory Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...

. Sanguivorous species usually feed on a variety of other animals, using their proboscis to host's skin. They generate

anticoagulants Anticoagulants, commonly known as blood thinners, are chemical substances that prevent or reduce coagulation of blood, prolonging the clotting time. Some of them occur naturally in blood-eating animals such as leeches and mosquitoes, where they ...

(like

mosquitoes Mosquitoes (or mosquitos) are members of a group of almost 3,600 species of small Diptera, flies within the family Culicidae (from the Latin ''culex'' meaning "gnat"). The word "mosquito" (formed by ''mosca'' and diminutive ''-ito'') is Spanish ...

) and natural anaesthetia to help the feeding. Predatory Rhynchobdellidae have digestive enzymes that help break down their prey, which usually consists of small invertebrates such as insect larvae or

amphipods Amphipoda is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods range in size from and are mostly detritivores or scavengers. There are more than 9,900 amphipod species so far describ ...

Families

Glossiphoniidae (Freshwater jawless leeches)

The Glossiphoniidae, the freshwater jawless leeches, or leaf leeches (due to their shape) are freshwater leeches, flattened, and with a poorly defined anterior sucker. The family Glossiphoniidae contains one of the world's largest species of leech, the giant Amazon leech, which can grow up to 45 cm in length. Many species show extended parental care, keeping eggs in nests or pouches and caring for and feeding the young. They feed on both vertebrate and invertebrate animals.

Piscicolidae (Fish leeches)

The Piscicolidae occur in both freshwater and

seawater Seawater, or salt water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/L, 35 ppt, 600 mM). This means that every kilogram (roughly one liter by volume) of seawater has appr ...

, have cylindrical bodies, and a usually well-marked, bell-shaped, anterior sucker. They are parasites of fish. The family was originally divided into three subfamilies based on species' pulsatile vesicles, but the subfamilies were disbanded in 2006. Ozobranchus jantseanus cropped

Ozobranchidae (Turtle leeches)

Ozobranchidae are primarily parasitic on marine turtles, and are sometimes merged with the Piscicolidae.

References