Arhynchobdellida
Encyclopedia
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 clade
s of clitellate
annelid
s - and whether the clitellates are themselves a clade - have not been fully elucidated. For example, the "true leeches" (Euhirudinea
) might actually be synonymous with the Hirudinea, as all other leech-like annelids might not be very closely related to the true leeches.
Proboscisless leeches are generally freshwater
or amphibious animals. They have usually 6-8, sometimes 5 pairs of eye
s. Some - among them the well-known European Medical Leech (Hirudo medicinalis) of the Hirudiniformes
- are bloodsuckers, while most - including the Kinabalu Giant Red Leech
(Mimobdella buettikoferi) of the Erpobdelliformes - are predators that hunt small invertebrate
s which are swallowed whole.
Arhynchobdellida systematics has been revised in modern times. Formerly it was believed that they can be divided into a jawed and a jawless order
. However, the lack of jaws does not denote a particularly close relationship. Jawed leeches are more numerous but exclusively found among the Hirudiniformes
, while the jawless "Pharyngobdellida" (or "Pharyngobdellae"), also known as "worm-leeches", are more diverse and occur in the Hirudiniformes and the Erpobdelliformes alike.
In addition to the two orders accepted today, there is a more basal lineage. These, the Americobdellidae, are not assigned order rank but treated as a family to signify their phylogenetic position near the base of the Arhynchobdellida. They are massive annelids, measuring 30 long in some cases, and are anatomically primitive. These animals hunt earthworm
s, which they suck in in one piece through their toothless mouth.
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
of the Hirudinea. But leech taxonomy
Taxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...
and systematics
Systematics
Biological systematics is the study of the diversification of terrestrial life, both past and present, and the relationships among living things through time. Relationships are visualized as evolutionary trees...
will eventually be revised in due time, not because there are many uncertainties about their phylogeny, but because the major 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...
s of clitellate
Clitellata
Clitellata is a class of Annelid worms, characterized by having a clitellum - the 'collar' that forms a reproductive cocoon during part of their life cycle. The clitellates comprise around 8,000 species...
annelid
Annelid
The annelids , formally called Annelida , are a large phylum of segmented worms, with over 17,000 modern species including ragworms, earthworms and leeches...
s - and whether the clitellates are themselves a clade - have not been fully elucidated. For example, the "true leeches" (Euhirudinea
Euhirudinea
Euhirudinea, the true leeches, are an infraclass of the Hirudinea. These clitellate annelids are of somewhat unclear relationships; namely the relationships of Hirudinea with oligochaetes are in need of revision...
) might actually be synonymous with the Hirudinea, as all other leech-like annelids might not be very closely related to the true leeches.
Proboscisless leeches are generally freshwater
Freshwater
Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...
or amphibious animals. They have usually 6-8, sometimes 5 pairs of eye
Eye
Eyes are organs that detect light and convert it into electro-chemical impulses in neurons. The simplest photoreceptors in conscious vision connect light to movement...
s. Some - among them the well-known European Medical Leech (Hirudo medicinalis) of the Hirudiniformes
Hirudiniformes
The Hirudiniformes are one of the currently-accepted suborders of the proboscisless leeches . Their most well-known member is the European Medical Leech, Hirudo medicinalis, and indeed most of the blood-sucking "worms" as which leeches are generally perceived belong to this group...
- are bloodsuckers, while most - including the Kinabalu Giant Red Leech
Kinabalu giant red leech
The Kinabalu giant red leech is a large bright orange-red coloured leech that is endemic to Mount Kinabalu, Borneo. Very little is known about this animal although it has been identified as Mimobdella buettikoferi Blanchard, 1897....
(Mimobdella buettikoferi) of the Erpobdelliformes - are predators that 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 which are swallowed whole.
Systematics and taxonomy
Given the systematic uncertainties, the proboscisless leeches have been treated at varying ranks, and the alternate name Arhynchobdellae is also sometimes found.Arhynchobdellida systematics has been revised in modern times. Formerly it was believed that they can be divided into a jawed and a jawless order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
. However, the lack of jaws does not denote a particularly close relationship. Jawed leeches are more numerous but exclusively found among the Hirudiniformes
Hirudiniformes
The Hirudiniformes are one of the currently-accepted suborders of the proboscisless leeches . Their most well-known member is the European Medical Leech, Hirudo medicinalis, and indeed most of the blood-sucking "worms" as which leeches are generally perceived belong to this group...
, while the jawless "Pharyngobdellida" (or "Pharyngobdellae"), also known as "worm-leeches", are more diverse and occur in the Hirudiniformes and the Erpobdelliformes alike.
In addition to the two orders accepted today, there is a more basal lineage. These, the Americobdellidae, are not assigned order rank but treated as a family to signify their phylogenetic position near the base of the Arhynchobdellida. They are massive annelids, measuring 30 long in some cases, and are anatomically primitive. These animals hunt earthworm
Earthworm
Earthworm is the common name for the largest members of Oligochaeta in the phylum Annelida. In classical systems they were placed in the order Opisthopora, on the basis of the male pores opening posterior to the female pores, even though the internal male segments are anterior to the female...
s, which they suck in in one piece through their toothless mouth.