Hirudiniformes
Encyclopedia
The Hirudiniformes are one of the currently-accepted suborders of the proboscisless leech
es (Arhynchobdellida
). Their most well-known member is the European Medical Leech, Hirudo medicinalis, and indeed most of the blood-sucking "worm
s" as which leeches are generally perceived belong to this group. In general, though some leeches suck blood, many are predators which hunt small invertebrate
s.
The Arhynchobdellida were formerly divided into two groups, denoted by presence or absence of toothed jaws. But this does not represent a natural division, as has now been determined - the most primitive proboscisless leeches are not found among the jawed blood-sucking forms as was generally believed, but among the jawless predators.
"Jawed leeches" - termed "Gnathobdellae" or "Gnathobdellida" - are exclusively found among the Hirudiniformes, but the order contains a number of jawless families
as well. The jawed, toothed forms make up the aquatic
Hirudidae and the terrestrial
Haemadipsidae and Xerobdellidae
(sometimes included in the preceding but worthy of recognition as an independent family). These might actually form a clade
, which would then be placed at superfamily rank, but it seems that the Hirudidae might rather be close relatives of the carnivorous Haemopidae instead.
Many of the most well-known leeches belong to this family, most notably the medical leeches, such as the European species
, already mentioned, which is prominent among these. Other medical Hirudiniformes of lesser importance are for example other species of the genus
Hirudo, the North American Medical Leech (Macrobdella decora), and the Asian Medical Leech (Hirudinaria manillensis). Among the better-known bloodsucking land leeches are the Indian Leech (Haemadipsa sylvestris) and the yamabiru or Japanese Mountain Leech (Haemadipsa zeylanica).
Leech
Leeches are segmented worms that belong to the phylum Annelida and comprise the subclass Hirudinea. Like other oligochaetes such as earthworms, leeches share a clitellum and are hermaphrodites. Nevertheless, they differ from other oligochaetes in significant ways...
es (Arhynchobdellida
Arhynchobdellida
The proboscisless leeches, Arhynchobdellida, are classified as an order of the Hirudinea. But leech taxonomy and systematics will eventually be revised in due time, not because there are many uncertainties about their phylogeny, but because the major clades of clitellate annelids - and whether the...
). Their most well-known member is the European Medical Leech, Hirudo medicinalis, and indeed most of the blood-sucking "worm
Worm
The term worm refers to an obsolete taxon used by Carolus Linnaeus and Jean-Baptiste Lamarck for all non-arthropod invertebrate animals, and stems from the Old English word wyrm. Currently it is used to describe many different distantly-related animals that typically have a long cylindrical...
s" as which leeches are generally perceived belong to this group. In general, though some leeches suck blood, many are predators which hunt small invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
s.
The Arhynchobdellida were formerly divided into two groups, denoted by presence or absence of toothed jaws. But this does not represent a natural division, as has now been determined - the most primitive proboscisless leeches are not found among the jawed blood-sucking forms as was generally believed, but among the jawless predators.
"Jawed leeches" - termed "Gnathobdellae" or "Gnathobdellida" - are exclusively found among the Hirudiniformes, but the order contains a number of jawless families
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
as well. The jawed, toothed forms make up the aquatic
Aquatic animal
An aquatic animal is an animal, either vertebrate or invertebrate, which lives in water for most or all of its life. It may breathe air or extract its oxygen from that dissolved in water through specialised organs called gills, or directly through its skin. Natural environments and the animals that...
Hirudidae and the terrestrial
Terrestrial animal
Terrestrial animals are animals that live predominantly or entirely on land , as compared with aquatic animals, which live predominantly or entirely in the water , or amphibians, which rely on a combination of aquatic and terrestrial habitats...
Haemadipsidae and Xerobdellidae
Xerobdellidae
Xerobdellidae are a small family of "jawed leeches". The latter might be a natural, monophyletic group of hirudiniform proboscisless leeches. Xerobdellidae have three jaws and five pairs of eyes, the fourth and fifth being separated by one or two eyeless segments...
(sometimes included in the preceding but worthy of recognition as an independent family). These might actually form a clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
, which would then be placed at superfamily rank, but it seems that the Hirudidae might rather be close relatives of the carnivorous Haemopidae instead.
Many of the most well-known leeches belong to this family, most notably the medical leeches, such as the European species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
, already mentioned, which is prominent among these. Other medical Hirudiniformes of lesser importance are for example other species of the genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Hirudo, the North American Medical Leech (Macrobdella decora), and the Asian Medical Leech (Hirudinaria manillensis). Among the better-known bloodsucking land leeches are the Indian Leech (Haemadipsa sylvestris) and the yamabiru or Japanese Mountain Leech (Haemadipsa zeylanica).