Hirudo orientalis is a species of medicinal leech. It has confused with Hirudo medicinalis, but has recently been recognized as different species. This Asian species is associated with mountainous areas in the subboreal eremial zone and occurs in Azerbaijan, Iran, Uzbekistan and Kazakhstan. It occurs also in Georgia, and probably in Armenia.
Length up to 108 mm, width of maximum body 10 mm, width of anterior sucker 4 mm, width of posterior sucker 5.5 mm. Gonopores are separated by five annuli. There are complete somite fiveannulate. Body surface is covered with numerous papillae. There are five eye pairs. Sulcus is present as a narrow and distinct groove running from the crypt of the median dorsal jaw to the dorsal rim of the anterior sucker. Dorsal surface color is mainly grass green, there are two orange paramedian stripes which are thin and fragmented and two orange paramarginal stripes which are broad and encompassing black segmentally arranged quadrangular or rounded spots. Lateral margins of body with yellow stripes encompassing black, segmentally arranged rounded spots. Black spots are located on the central annulus (a2) of each segment. Ventral region is mainly black, with metameric pairs of light greenish markings.
Jaws and Teeth: This species has tree jaws, typically medicinal leech, which are monostichodont and bearing papillated. Papillae have not any pores or fissures. Each jaws have 80 (min: 71 – max: 91) teeth which their average size is 33 µm
Male reproductive system: Atrium is large, bulbous with a glandular cover and located at ganglion in segment XI. Penis sheath is long broad duct bent anteriorly, not reaching ganglion in segment XII. Epididymis are medium-sized, discoid, tightly packed masses of ducting standing upright on either side of the atrium and located between ganglia in segments XI and XII. Ejaculatory bulbs are fusiform, well developed, and not larger than epididymes the dorsocefalic faces of which they circle. Vas deferens is thin ducts running from epididymis posteriorly. Testisacs is ovoid, approximately 1.5 times the size of ovisacs and located posterior to ganglion in segment XIII.
Female reproductive system: Vagina has an upright, long, evenly curved tube entering directly into ventral body wall posterior to ganglion in XII. Common oviduct enters the vagina subterminally at a small vaginal caecum. Ovisacs are globular, small. Common oviduct has a thin duct forming several loops and covered with a thick layer of glandular tissue bound to the cephalic face of vagina. Entire female reproductive system located between ganglia XII and XIII.
The mature individuals deposit average 2.53 cocoons within one month. Each cocoon has averagely 8.55 hatchlings. According to these figures, H. orientalis deposite more cocoon than H. medicinalis (1.65), but less than Hirudo verbana (3.29). Hatchlings number per cocoon is also medium compared to the previous species (H. medicinalis: 6.73, H. verbana: 10.45)
^ a b c d e Utevsky, S. Y., & Trontelj, P. (2005). A new species of the medicinal leech (Oligochaeta, Hirudinida, Hirudo) from Transcaucasia and an identification key for the genus Hirudo. Parasitology research, 98(1), 61-66. DOI: 10.1007/s00436-005-0017-7
^ Siddall, M. E., Trontelj, P., Utevsky, S. Y., Nkamany, M., & Macdonald, K. S. (2007). Diverse molecular data demonstrate that commercially available medicinal leeches are not Hirudo medicinalis. Proceedings of the Royal Society of London B: Biological Sciences, 274(1617), 1481-1487. DOI: 10.1098/rspb.2007.0248
^ Utevsky, S., Zagmajster, M., Atemasov, A., Zinenko, O., Utevska, O., Utevsky, A., & Trontelj, P. (2010). Distribution and status of medicinal leeches (genus Hirudo) in the Western Palaearctic: anthropogenic, ecological, or historical effects?. Aquatic Conservation: Marine and Freshwater Ecosystems, 20(2), 198-210 DOI: 10.1002/aqc.1071
^ Kovalenko, M. V., & Utevsky, S. Y. (2015). Comparative structural analysis of jaws of selected blood-feeding and predacious arhynchobdellid leeches (Annelida: Clitellata: Hirudinida). Zoomorphology, 134(1), 33-43. DOI: 10.1007/s00435-014-0245-4
^ Petrauskienė, L., Utevska, O., & Utevsky, S. (2009). Can different species of medicinal leeches (Hirudo spp.) interbreed?. Invertebrate Biology, 128(4), 324-331. DOI: 10.1111/j.1744-7410.2009.00180.x