Leeches are segmented parasitic or predatory worms, Helobdella stagnalis, in its freshwater habitat
· 27.06.2023 · 17:28:02 ··· Dienstag ⭐ 0 🎬 0
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Leeches are segmented parasitic or predatory worms, Helobdella stagnalis, in its freshwater habitat
Helobdella is a genus of leeches in the family Glossiphoniidae, the freshwater jawless leeches. They occur worldwide.
These are small, flat leeches which do not feed on blood.
Several species in this genus are used as model organisms in the study of developmental biology.
It has been difficult to define species in this genus without DNA analysis. Like other leeches in this family, some Helobdella species are polymorphic, coming in different colors and patterns. On the other hand, some uniformly colored species are actually cryptic species complexes that may be divided into separate species with genetic analysis.
As of 2004 there were approximately 40 described species, with species being described and reclassified continually.
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 bodies that can lengthen and contract. Both groups are hermaphrodites and have a clitellum, but leeches typically differ from the oligochaetes in having suckers at both ends and in having ring markings that do not correspond with their internal segmentation. The body is muscular and relatively solid, and the coelom, the spacious body cavity found in other annelids, is reduced to small channels.
The majority of leeches live in freshwater habitats, while some species can be found in terrestrial or marine environments. The best-known species, such as the medicinal leech, Hirudo medicinalis, are hematophagous, attaching themselves to a host with a sucker and feeding on blood, having first secreted the peptide hirudin to prevent the blood from clotting. The jaws used to pierce the skin are replaced in other species by a proboscis which is pushed into the skin. A minority of leech species are predatory, mostly preying on small invertebrates.
The eggs are enclosed in a cocoon, which in aquatic species is usually attached to an underwater surface; members of one family, Glossiphoniidae, exhibit parental care, the eggs being brooded by the parent. In terrestrial species, the cocoon is often concealed under a log, in a crevice or buried in damp soil. Almost seven hundred species of leech are currently recognised, of which some hundred are marine, ninety terrestrial and the remainder freshwater.
Leeches have been used in medicine from ancient times until the 19th century to draw blood from patients. In modern times, leeches find medical use in treatment of joint diseases such as epicondylitis and osteoarthritis, extremity vein diseases, and in microsurgery, while hirudin is used as an anticoagulant drug to treat blood-clotting disorders.
The leech appears in the biblical Book of Proverbs as an archetype of insatiable greed. The term "leech" is used to characterise a person who takes without giving, living at the expense of others.
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