Macrobdella decora

Macrobdella decora
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Annelida
Clade:	Pleistoannelida
Clade:	Sedentaria
Class:	Clitellata
Subclass:	Hirudinea
Order:	Arhynchobdellida
Family:	Macrobdellidae
Genus:	Macrobdella
Species:	M. decora
Binomial name
Macrobdella decora (Say, 1824)
Observed
Synonyms[1]
Hirudo decora Say, 1824

Macrobdella decora, also known as the North American medicinal leech, is a species of freshwater

Macrobdella decora is found in North America east of the Rocky Mountains: in southern Canada and the neighbouring parts of the United States. There is, however, one disjunct population of leeches living in northern Mexico. The species may be panmictic across most of its range, but the question remains unanswered and further research into the topic is needed. It is not considered to be endangered. The saliva of M. decora contains a blood thinner dubbed "decorsin" which may be unique to the species. A comparison of the saliva of M. decora and that of European species has lead researchers to the conclusion that blood-sucking in jawed leeches likely evolved from a single origin.

Macrobdella decora was originally placed in the genus Hirudo by Thomas Say, who described it in 1824 in an appendix to a book about an expedition up the Minnesota River. Three other species were described in the same pages: Placobdella parasitica, Nephelis lateralis, and Haemopis marmorata. Besides a brief physical description, Say noted that the species was "much smaller" than the other leeches he had described and was "comparatively rare."^[2] When Addison Emery Verrill erected the genus Macrobdella in 1872, he transferred Say's species into his new genus.^[3]: 138 Macro simply means big, while bdella means "leech" in Greek.^[4] It is commonly known as the North American medicinal leech.^[5]

Macrobdella decora is the

Macrobdella decora is a medium-sized leech, growing between 5 and 8.5 cm (2.0 and 3.3 in) long, and weighing from 1.48 to 3.69 grams (0.052 to 0.130 oz).[8]^{: 67 [9]: 155} It has a dark green, brown or olive-green back with a line of 20 or so small orange or red dots down the middle, and two corresponding sets of black dots on its sides. Its underbelly is reddish with black spots dispersed irregularly across it.^{[8]: 67 [2][10][11]: 160} Its back is rounded but its belly is flattened.^{[11]: 160 [12]: 230} All leeches have 32 segments, but they are all also covered with external rings called annuli;^[13] the body of M. decora has between 90 and 94 annuli total.

The head of M. decora is rounded and has ten

All leeches are hermaphrodites whose male reproductive organs mature first and the female ones later.^[17] M. decora has ten pairs of testisacs located from segments thirteen to twenty-three, with large, compact, and much-coiled epididymes, and crescent-shaped or globular ovisacs which are located in the thirteenth segment. A 2023 paper described the leech's oviducts as "thin" and "torturously folded".^{[9]: 155 [14]: 510} The male and female gonopores, which are external openings to the internal reproductive organs,^[18][19] are usually separated by five annuli, or external rings; this degree of separation is an important feature for identifying the species.^{[20][8]: 67} The male gonopore, when withdrawn, appears as nothing more than a hole in between segments eleven and twelve; however, when the male gonopore and its surrounding parts are everted, they appear as a small cone, with the organ at the tip and having deeply furrowed sides. The leech's four copulatory glands are arrayed in a square in an area of rough skin on segments thirteen and fourteen.^[14]: 509

Leech saliva is known to contain several compounds, including hirudin, an anti-coagulant.^[21][22] The saliva of M. decora is also known to contain several substances not previously all identified from the same leech, as well as an anticoagulant dubbed decorsin which might be unique to M. decora. The transcriptome of M. decora saliva was described in 2010.^[22] A 2019 paper published in the Journal of Parasitology compared hirudin and decorsin from M. decora, as well as hirudin and "hirudin-like factors" – substances which resemble hirudin but are not known to act as anticoagulants – obtained from European species. The authors concluded that that blood-sucking among jawed leeches evolved from a single origin.^{[23]: 423–4}

Being the most widely

Macrobdella decora is a freshwater species that is found in still or slow-moving water bodies such as streams, temporary ponds, ditches, and wetlands.[8]^{: 67 [26][27]} They are particularly common in temporary ponds; the leeches are able to burrow into the bottom when the pond dries up.^[28]: 417 In lakes, the leeches are most active in the epilimnion, or top-most layer.^[29]: 3

In Ontario, NatureServe lists the species as "Secure", but no assessment has been completed for other regions.^[30] M. decora was described as unendangered in 2021 paper proposing its use as a model for digestive tract symbioses.^[5]: 1

Macrobdella decora is both parasitic and

The leeches engorge themselves with blood before mating. One or two months after feeding, they produce spongy cocoons, which are pale yellow and elliptical in shape. About another month later, the young, only 20 to 22 millimetres (0.79 to 0.87 in) long, emerge.[8]^: 68 They will take several years to become fully mature.^[33]

The

Macrobdella decora does parasitize humans and is often found by people swimming in Canada and the northern United States. Sometimes swimming areas have had to be restricted or even closed due to the leech's presence.[8]^: 67 Historically, M. decora was in fact not used very much in bloodletting, despite its common name as a "medicinal leech".^[5]: 2 However, there is some evidence of their medicinal use as a replacement to the European medicinal leeches, specifically in Philadelphia during the 19th century.^[24] Indeed, Addison Emery Verrill, writing in 1872, noted M. decora's use by doctors as a stand-in for "imported leeches", and he noted the North American species was "equally efficacious".^[3]: 132 It is possible that human leech-trading helped move leeches between water bodies; today, they are sometimes used as and transported for fishing bait, but they are not a very favoured choice.^[24]