Euhirudinea, the true leeches, are an
infraclass
In biology, taxonomic rank (which some authors prefer to call nomenclatural rank because ranking is part of nomenclature rather than taxonomy proper, according to some definitions of these terms) is the relative or absolute level of a group of or ...
of the
Hirudinea
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 ...
.
Taxonomy
These
clitellate annelid
The annelids (), also known as the segmented worms, are animals that comprise the phylum Annelida (; ). The phylum contains over 22,000 extant species, including ragworms, earthworms, and leeches. The species exist in and have adapted to vario ...
s are of somewhat unclear relationships; namely the relationships of Hirudinea with
oligochaetes are in need of revision. It may be that the presumed
sister taxon
In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree.
Definition
The expression is most easily illustrated by a cladogram:
Taxon A and ...
of the Euhirudinea, the
Acanthobdellidea, turns out to be more distantly related, as was already the case with the
Branchiobdellida
Branchiobdellida is an order of freshwater leech-like clitellates that are obligate ectosymbionts or ectoparasites, mostly of astacoidean crayfish. They are found in the Northern Hemisphere and have a holarctic distribution in East Asia, the E ...
. Thus, eventually Euhirudinea might become a
junior synonym
In taxonomy, the scientific classification of living organisms, a synonym is an alternative scientific name for the accepted scientific name of a taxon. The botanical and zoological codes of nomenclature treat the concept of synonymy differently.
...
of Hirudinea.
True leeches are subdivided into two groups, the
Arhynchobdellida or Arhynchobdellae (proboscisless leeches), and the
Rhynchobdellida or Rhynchobdellae (jawless leeches). Note that the lack of jaws is a
plesiomorph
In phylogenetics, a plesiomorphy ("near form") and symplesiomorphy are synonyms for an ancestral Phenotypic trait, character shared by all members of a clade, which does not distinguish the clade from other clades.
Plesiomorphy, symplesiomorph ...
y, while the presence of a proboscis is an
apomorph
In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to ha ...
y – not all Arhynchobdellida have jaws, but all Rhynchobdellida have a proboscis. The best-known leech
species
A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
, ''
Hirudo medicinalis
''Hirudo medicinalis'', or the European medicinal leech, is one of several species of leeches used as medicinal leeches.
Other species of ''Hirudo'' sometimes also used as medicinal leeches include ''Hirudo orientalis, H. orientalis'', ''Hirudo ...
'' (European Medical Leech), belongs to the Arhynchobdellida.
Ecology
Euhirudinea leeches tend to hunt for nutrients in the morning or afternoon. Leeches that hunt in the morning are found in larger sizes than those who hunt in the afternoon. Therefore, feeding in the morning seems to be more nutritious for the leeches than in the afternoon. Terrestrial Euhirudinea leeches, which inhabit tropical or subtropical environments have been found a greater number on-trails compared to off-trail numbers.
References
Leeches
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