Evolution and systematics

Leeches are utterly soft-bodied animals and couldn't be anticipated to go away a marked fossil document. Although there are two putative fossils from Bavarian deposits courting from the Upper Jurassic interval (about 145 million years in the past), Epitrachys rugosus (Ehlers, 1869) and Palaeohirudo eichstaettensis (Kozur, 1970), neither has each the definitive caudal sucker and the ring-shaped subdivisions of the physique that might outline them as leeches. The evolutionary relationships of leeches reveal that the ancestral hirudinid was a blood feeder in a freshwater surroundings. This discovering means that leeches aren't any older than vertebrates and possibly no older than amphibians. The phylogenetic relationships of leeches have been the topic of a number of analyses based mostly on morphological (structural) characters and DNA sequence knowledge. Taken collectively, these analyses reveal past query that leeches, branchiobdellidans (crayfish worms) and acanthobdellidans kind a monophyletic (descended from a standard taxon) group of oligochaetes that's intently associated to the lumbriculid oligochaetes, or earthworms. Leeches are subdivided first into suborders based mostly on anatomical diversifications for feeding. The Rhynchobdellida, as their title implies, have a muscular proboscis that enables them to feed on blood drawn from tissues beneath an organism’s pores and skin which can be properly provided by blood vessels. The massive worm-like Arhynchobdellida, of which Hirudo medicinalis is typical, have three muscular jaws, every of which can be armed with a row of enamel making a serrated innovative. The two principal households of proboscis-bearing Rhynchobdellida have pairs of medial cephalic eyespots that may detect two-dimensional motion. The Piscicolidae household includes small elongate, largely marine species that feed seasonally on fishes. The Glossiphoniidae have a tendency to be strongly dorsoventrally flattened freshwater species usually preferring anuran (frogs and toads) or chelonian (turtles and tortoises) hosts, although just a few are particular to fishes and others will feed on mammals. The blood-feeding arhynchobdellids embrace the massive aquatic Hirudinidae (medicinal leeches) and the smaller terrestrial Haemadipsidae (jungle leeches). The jungle leeches are extra frequent within the humid forests of Southern Asia, India, Madagascar, Australia, and Indonesia than their aquatic cousins. Both of these teams are geared up with a parabolic arc of 10 eyespots that detect motion in three dimensions. Terrestrial leeches have the extra adaptation of respiratory auricles close to their caudal sucker that let gasoline change with out extreme lack of fluid. These leeches even have welldeveloped sensory techniques for detecting vibrations, carbon dioxide, and warmth. In addition, there are a number of predatory arhynchobdellids just like the slender Erpobdelliformes (households Erpobdellidae, Salifidae, and Americobdellidae); the bigger amphibious Haemopidae; and several other different poorly studied households.

Physical traits

Leeches have a clitellum, or specialised saddle-shaped glandular phase, that secretes cocoons or egg circumstances. These animals are simultaneous hermaphrodites. They have a physique consisting of 34 physique segments (somites) however lack the chaetae (stiff hairs or bristles) of different annelids. Though not all are sanguivorous, many leeches have particular diversifications for blood feeding. Principal amongst these is the muscular caudal sucker made up of the final seven somites of the segmented physique. The sucker is crucial for attaching to and remaining on a bunch. It could double as a strong swimming fluke (anchor) in bigger and extra energetic species. The six somites on the entrance of the leech are also modified right into a area with a ventral sucker surrounding a muscular pharynx. Negative strain utilized by this anterior sucker aids in attachment and in encouraging blood to circulation from a chunk wound. Blood-feeding leeches often are geared up with massive branched gastric caeca, or pouches, that permit them to increase significantly throughout feeding; some leeches devour up to six occasions their unfed physique weight. The reality that each one present-day blood-feeding leeches have these options means that the ancestral leech additionally had them.

Distribution

Leeches will be present in one kind or one other in freshwater and terrestrial places on all continents besides Antarctica. Marine leeches are present in all oceans. The main households of leeches have international distributions apart from some species within the Haemadipsidae household. These species seem to have originated on the time of the late Gondwanan continental separation, after Africa and South America had parted from the rest of the unique supercontinent about 180–140 million years in the past. Some minor households, together with the Americobdellidae and Cylicobdellidae, are discovered solely in South America. Most oceanic leeches appear to favor temperate or arctic waters, with just a few species particular to elasmobranchs being present in tropical marine techniques.

Habitat

The frequency with which leeches are encountered depends upon geography. Most species that happen in European, African, or North and South American freshwater ecosystems will be discovered beneath submerged rocks and particles or alongside shorelines when they don't seem to be feeding on their respective hosts. Terrestrial leeches are discovered solely in such perpetually moist environments as tropical or temperate coastal rainforests, the place they continue to be in leaf litter except they're searching for a meal. The habits of marine leeches should not properly understood, as they're mostly encountered whereas they're feeding on fishes or turtles. Few leeches seem to choose particular websites on the hosts they feed from.

Behavior

Many leeches can swim by coordinating the depolarization of nerve cells alongside their ventral wire, which causes the longitudinal muscle groups to transfer the leech’s physique in a curving or wavelike sample. The posterior sucker serves as an anchor to present thrust. Leeches transfer alongside stable substrates by alternating attachment of their anterior and posterior suckers between durations of physique stretching— very similar to the motion of an inchworm. When at relaxation throughout lengthy durations of digestion or whereas brooding younger, leeches lie beneath objects alongside the shorelines, usually partially out of water. They regularly are noticed performing their wavelike swimming motion in place as if to help in air flow. Leeches have a number of anterior eyespots and are ready to detect motion from contrasting patterns of sunshine and shadow.

Feeding ecology and eating regimen

Sanguivorous (blood-feeding) leeches are able to residing on blood due to plenty of bioactive chemical compounds of their saliva. Vertebrate blood, together with human blood, is provided with coagulation (clotting) elements. Most leeches require 30 minutes or extra for feeding; nevertheless, vertebrate blood can clot in a lot much less time. If the blood that the leech ingests have been to clot inside its digestive tract, it couldn't mate, keep away from its predators, or search one other meal. Leeches have circumvented the endpoints of the mammalian coagulation cascade, which is the medical time period for the method of blood clotting. The coagulation cascade consists of the clumping of platelets, the manufacturing of a fibrin matrix (community), and the cross-linking of that matrix right into a agency clot. Leeches can intervene with this clotting system at a minimal of seven totally different factors. Hirudin, a potent thrombin inhibitor, was the primary anticoagulant (blood-thinning) compound to be remoted from leech saliva. Most different leech-derived anticoagulants are additionally protease inhibitors. Some sanguivorous species are very host-specific; Placobdelloides jaegerskioeldi feeds completely on Hippopotamus amphibius, for instance, whereas different leeches are much less discriminating. Of the marine species, those who feed on cartilaginous fishes present no real interest in teleosts (bony fishes), and Ozobranchus species feed solely on turtles. In freshwater environments, the massive and infamous hirudinid medicinal leeches extra usually purchase their nourishment from amphibians or fishes than from swimming people. Many leeches don't feed on blood in any respect. Glossiphoniids, like species of Helobdella and Glossiphonia, feed on aquatic oligochaetes and snails. The jawless Erpobdellidae feed on chironomid (midge) larvae, and the jawed haemopids devour complete earthworms, shredding them with jaws bearing two rows of huge enamel. In addition, there are not often encountered households just like the South American Americobdellidae and Cylicobdellidae. The species in these households are terrestrial earthworm hunters and of unsure phylogenetic affinities. Researchers have usually assumed that nonbloodfeeding types of leeches are extra primitive than these with the “advanced” conduct of blood feeding. Recent phylogenetic work factors to the existence of a blood feeding ancestor, nevertheless, and at the very least six transformations to predation within the historical past of leeches.

Reproductive biology

Leeches are hermaphroditic animals with separate female and male reproductive techniques. Male and feminine techniques open independently to the outside, every by way of a small ventral gonopore located on the midventral line within the clitellar somites. The commonest type of ####ual activity in leeches is traumatic insemination (direct injection into the feminine’s physique cavity). Male leeches randomly implant their spermatophores (small packets containing sperm) within the cuticle or outer overlaying of a recipient mate. The bigger hirudinids and terrestrial haemadipsids have anatomical diversifications for inside fertilization, together with a protrusible penis and a receptive vaginal sac allowing direct contact between female and male gonopores. Reproducing people are often distinguishable by the swelling of a sure variety of annuli within the area that features their gonopores. This swollen space constitutes the clitellum, a glandular phase that secretes the cocoons or egg circumstances. Unlike the homologous construction in terrestrial earthworms, the diploma of prominence of the clitellum varies significantly in leeches. The fish leeches, or Piscicolidae, exhibit an adaptation that helps their offspring to discover an early blood meal. Rather than abandoning a secreted cocoon because the oligochaetes and plenty of leeches do, the piscicolids cement their egg circumstances to the floor of crustaceans. When a fish eats the crustacean, the younger leeches readily connect to the fish host’s buccal (cheek) surfaces and migrate to its gills. Such Glossiphoniidae as Haementeria ghilianii are broad and flattened, and usually discovered feeding on turtles or amphibians. Species on this household secrete a membranous bag that holds their eggs on their underside in a brooding place beneath rocks and different particles. When the brood hatches, the younger will flip and fix themselves to their guardian’s venter, or stomach. When the guardian finds its subsequent blood meal, the younger are carried to their first blood meal.

Conservation standing

The European medicinal leech, Hirudo medicinalis, has been overexploited. In addition, its pure habitat has turn into fragmented and extremely restricted. This species is listed as Lower Risk/Near Threatened by the IUCN, and can be listed in CITES Appendix II. Many terrestrial rainforest species are as threatened as their particular habitats; examples embrace Mesobdella gemmata within the Valdivian coastal forests of Chile and Haemadipsa sumatrana.

Significance to people

Leeches have been well-known for his or her medicinal functions within the eighteenth and nineteenth centuries, once they have been used for such functions as assuaging complications and treating weight problems. It is unlikely that any of these therapies have been profitable. Leeches are actually, nevertheless, experiencing a renaissance of curiosity in medication and pharmacology: they're the instruments of alternative for treating postoperative hematomas (localized collections of clotted blood) in microsurgery. In addition, their highly effective salivary anticoagulants are being studied as potential remedies for coronary heart illness and even most cancers. Leeches are additionally potential indicator species for sure measurements of water high quality, together with heavy steel contamination and dissolved oxygen content material.