Suborder Glossiphoniiformes Tessler & de Carle, 2018
Family Glossiphoniidae Vaillant, 1890
Comments. Our two-locus phylogeny reveals the presence of two large clades, corresponding to the subfamilies Glossiphoniinae and Haementeriinae (Fig. 1). The subfamily Theromyzinae Sawyer, 1986, delineated by some authors2,10,22, was not supported as a distant phylogenetic clade and their representatives are clustered within the monophyletic Glossiphoniinae. The same pattern was recovered by earlier phylogenetic reconstructions3,30,33,34. These data indicate that Theromyzinae may represent a synonym of the latter subfamily. However, a subfamily-level revision of the Glossiphoniidae is beyond the framework of the present study.
Subfamily Glossiphoniinae Vaillant, 1890
Genus Alboglossiphonia Lukin, 1976
Type species: Alboglossiphonia heteroclita (Linnaeus, 1761) (= Hirudo heteroclita Linnaeus, 1761; by original designation).
Arctic occurrences. Our results reveal that members of this genus are not common inhabitants of the Arctic but two species, A. heteroclita (Linnaeus, 1761) and A. sibirica sp. nov., cross the Arctic Circle on the Yamal Peninsula through the Ob and Taz rivers (Table 1). Previously, it was shown that A. heteroclita occurs in the lower Ob Basin, northern edge of Western Siberia23.
Comments. This genus contains inconspicuous minute leeches and is characterized by a nearly global distribution1. It definitely requires an integrative taxonomic revision. Available genetic evidence (Fig. 1 and Supplementary Fig. S1) reveals that the North American populations of what was traditionally assigned to A. heteroclita should be considered a separate species, A. pallida (Verrill, 1872) (type locality: West River near New Haven, Connecticut, USA)35,36. Other species, which occurs in Siberia and the Far East, was tentatively assigned to Alboglossiphonia cf. papillosa (Braun, 1805) based on a darker pigmentation of its dorsum37,38 but it represents a separate North Asian species, which is described here.
Alboglossiphonia sibirica Bolotov, Eliseeva, Klass & Kondakov sp. nov
= Alboglossiphonia heteroclita Lukin (1957): 27339 (identification error).
= Alboglossiphonia heteroclita papillosa Kaygorodova et al. (2014): 337; Kaygorodova (2015): 4140 (identification error).
= Alboglossiphonia cf. papillosa Klass et al. (2018): 2638 (identification error).
Figures 4a, 5a, 7a, Supplementary Figs. S2a, S3a, S4, Supplementary Table S2.
LSID: https://zoobank.org/urn:lsid:zoobank.org:act:19B581C3-E912-487C-B9EC-8E50DDEFD380.
Holotype. RMBH Hir_0542_2-H (non-sequenced), RUSSIA: Lake Torfyanka, 43.0761° N, 131.9620° E, Vladivostok, Primorye, August 12, 2021, Y. E. Chapurina leg.
Paratypes (N = 13). RUSSIA: 1 specimen RMBH Hir_0542_2 (sequenced: COI sequence acc. No. ON873332), the type locality, the same date, and collector; 1 specimen RMBH Hir_0396 (non-sequenced), an oxbow lake of Taz River, near Tazovsky settlement, 67.5063° N, 78.6751° E, Yamal-Nenets Region, August 22, 2019, E. S. Babushkin leg.; 1 specimen RMBH Hir_0394 (DNA voucher; sequenced: COI sequence acc. No. ON548508), Vitim River, 57.2010° N, 116.4300° E, Lena River basin, Vitimsky Nature Reserve, Irkutsk Region, July 12, 2019, E. S. Babushkin leg.; 4 specimens RMBH Hir_0013 (3 sequenced with DNA vouchers and one placed on 36 permanent slides as a series of slices; COI sequence acc. No. MH286267, MH286268, and MH286269; 18S rRNA sequence acc. No. MH286273), between zooids of a bryozoan colony, small floodplain lake of the Lena River near Yakutsk, 62.3076° N, 129.8999° E, Yakutia Republic, August 20, 2017, I. N. Bolotov leg.; 1 specimen RMBH Hir_0417_2 (DNA voucher; sequenced: COI sequence acc. No. ON548511), Oron Lake, Gnilaya Kurya Bay, 57.1750° N, 116.4031° E, Lena River basin, Vitimsky Nature Reserve, Irkutsk Region, July 1, 2019, E. S. Babushkin leg.; 1 specimen RMBH Hir_0409_1 (sequenced: COI sequence acc. No. ON548509), a roadside ditch in Knevichi settlement, 43.3886° N, 132.1880° E, Primorye, September 10, 2020, O. V. Aksenova et al. leg.; 1 specimen RMBH Hir_0413 (sequenced: COI sequence acc. No. ON548510), a puddle near railway at Artem city, 43.3794° N, 132.2188° E, Primorye, September 10, 2020, O. V. Aksenova et al. leg.; 1 specimen RMBH Hir_0003_3 (DNA voucher; sequenced: COI sequence acc. No. MN393256), Tumnin River, 49.9451° N, 139.9181° E, Khabarovsk Region, July 14, 2014, I. N. Bolotov & I. V. Vikhrev leg.; 1 specimen RMBH Hir_0509_1 (sequenced: COI sequence acc. No. ON548516), a reservoir on the Bolshoy Alim River, near Tolstovka settlement, 50.1981° N, 127.9431° E, Amur Region, July 3, 2021, O. V. Aksenova et al. leg.; 1 specimen RMBH Hir_0510_1 (DNA voucher; sequenced: COI sequence acc. No. ON548517), an oxbow lake of Bureya River, near Novospassk, 49.6756° N, 129.7343° E, Amur Region, July 3, 2021, O. V. Aksenova et al. leg.
Etymology. The name of this species reflects its broad distribution in Siberia.
Differential diagnosis. Small leech, which could be distinguished from other congeners by a combination of the following characters: dorsum covered by numerous small, shallow, and indistinct papillae, light yellow, with multiple dark spots and short dashes arranged to 18–24 longitudinal rows; these spots and dashes merged into longitudinal lines in the anterior half of the body (the dark markings pattern often lost in ethanol-preserved animals). Externally, the new species is similar to A. heteroclita, A. hyalina (O. F. Müller, 1773), and A. striata (Apáthy, 1888). However, all these species do not have numerous dark spots and short dashes arranged to multiple longitudinal rows. Additionally, A. heteroclita differs from the new species by having a median row of segmentally arranged dark spots and a smooth dorsum without papillae. A. hyalina differs from A. sibirica sp. nov. by the general lack of dark pigmentation. A. striata differs from the new species by having a median row of segmentally arranged dark transverse stripes and a smooth dorsum without papillae.
Molecular diagnosis. The new species represents a separate genetic lineage but is more closely related to A. heteroclita (mean pairwise COI p-distance = 5.1%; range 4.9–5.4%). The intraspecific pairwise COI p-distance ranges from 0.0 to 2.1% (mean ± s.e.m. = 1.31 ± 0.10%; N = 14 sequences and 91 pairwise distance values). The GenBank acc. numbers of reference DNA sequences (COI and 18S rRNA) are given in Supplementary Table S2 and Supplementary Datasets S1–S2.
Description. Small leech (body length up to 11.9 mm). Measurements of the type series are given in Supplementary Table S2. Body broad, leaf-like, ovate. Dorsum with numerous small, shallow, and indistinct papillae. Posterior sucker small, circular (maximum diameter of 2.25 mm), ventrally directed. Proboscis pore in the center of anterior sucker. Coloration of living animals: body dirty yellow with multiple brown spots and dashes arranged to longitudinal rows; in the anterior half of the body, these spots and dashes merged into longitudinal lines. Coloration of ethanol-preserved animals: body light yellow; dorsum with multiple dark spots and short dashes arranged to 18–24 longitudinal rows; these spots and dashes merged into longitudinal lines in the anterior half of the body but the dark markings pattern often lost due to preservation. Three pairs of eyespots; the eyespots of the distal pair joined into a single spot; the eyespots of the next two pairs are spaced apart and fused together. Venter light yellow or whitish. Total number of annuli: 70. Somites I–IV joined to form a head region, somites V–XXIV triannulate, somites XXV–XXVII uniannulate. Gonopores joined and open in the furrow XIIa1/a2. Reproductive system: 6 pairs of large, bag-like testisacs inter-segmentally from XIII/XIV to XIX/XX; atrium small, spherical, the atrial cornua twisted anteriorly; paired ejaculatory ducts twisted, short; paired ovisacs narrow, very short. Digestive system: proboscis sheath massive, long, thick; salivary glands diffuse; crop with 6 pairs of crop caeca: 1st-5th uniform, bag-like, 6th pair (posterior caeca) with 3 blind processes; intestine with 4 pairs of rather short processes and an ovate extention after the last pair of processes.
Distribution. North Asia: Western Siberia, Eastern Siberia, the Russian Far East, and Mongolia39.
Habitats and ecology. This species is known to occur in a broad range of freshwater environments such as rivers, oxbow lakes, large to small natural lakes, reservoirs, road ditches, and even puddles (Supplementary Dataset S2). An unusual example of its association with a bryozoan species was described from Eastern Siberia38. Probably, the record of an Alboglossiphonia leech in the mantle cavity of an unidentified lymnaeid snail from the Altai Mountains, Russia41 could also be attributed to this species. The life cycle of the new species is unknown.
Genus Glossiphonia Johnson, 1816
Type species: Glossiphonia complanata (Linnaeus, 1758) (= Hirudo complanata Linnaeus, 1758; by subsequent designation).
Arctic occurrences. Representatives of this genus are the most remarkable component of the Arctic Glossiphoniidae fauna. Altogether seven species were recorded north of the Arctic Circle, two of which are new to science and described here (Table 1).
Comments. In general, sequenced representatives of the genus Glossiphonia could phylogenetically be delineated to three species groups (or subgenera): (1) the complanata-group (= subgenus Glossiphonia s. str.); (2) the verrucata-group (= subgenus Boreobdella Johansson, 1929; type species: Clepsine verrucata Müller, 1844); and (3) the concolor-group (= subgenus Paratorix Lukin & Epstein, 1960; type species: Torix baicalensis Stschegolew, 1922) (Table 1, Fig. 1 and Supplementary Fig. S1).
Glossiphonia arctica Bolotov, Eliseeva, Klass & Kondakov sp. nov
Figures 4B, 5b,c, 7c, Supplementary Figs. S2b, S3b, S5, Supplementary Table S2.
LSID: https://zoobank.org/urn:lsid:zoobank.org:act:FADF0993-A946-413A-9680-25BA0F9BE90D.
Holotype. RMBH Hir_0457_2_1-H (sequenced: COI sequence acc. No. ON810735; 18S rRNA sequence acc. No. ON819028), RUSSIA: a large lake near Sob’ railway station, 67.0480°N, 65.6316°E, Polar Urals, June 23, 2021, A. V. Kondakov et al. leg.
Paratypes (N = 18). 18 specimens RMBH Hir_0457 (two specimens sequenced: COI sequence acc. No. ON810736 and ON810737; 18S rRNA sequence acc. No. ON819029; one specimen placed on 18 permanent slides as a series of slices), the type locality, the same date, and collectors.
Etymology. The name of the new species indicates that its type locality is situated in the Arctic Region.
Differential diagnosis. Medium-sized leech, which could be distinguished from other congeners by a combination of the following characters: dorsum with four rows of ovate, broad but very shallow and indistinct papillae on annulus a2 (outer paramedian and inner paramarginal series); each papilla bears ovate light yellow or white spot; dorsal black markings pattern absent. Externally, the new species is similar to G. mollissima. However, the latter species differs from G. arctica sp. nov. by having larger papillae and a well-developed black markings pattern dorsally.
Molecular diagnosis. The new species represents a separate genetic lineage belonging to the verrucata-group (Fig. 1). The pairwise COI p-distance of the new species from other congeners varies from 7.0 to 12.4%. The intraspecific pairwise COI p-distance ranges from 0.0 to 0.2% (mean ± s.e.m. = 0.10 ± 0.05%; N = 3 sequences and 3 pairwise distance values). The GenBank acc. numbers of reference DNA sequences (COI and 18S rRNA) are given in Supplementary Table S2 and Supplementary Datasets S1–S2.
Description. Medium-sized leech (body length up to 13.3 mm). Measurements of the type series are given in Supplementary Table S2. Body broad, leaf-like, ovate. Dorsum with four rows of ovate, broad but very shallow and indistinct papillae on annulus a2 (outer paramedian and inner paramarginal series). Posterior sucker small, circular (maximum diameter of 1.9 mm), ventrally directed. Proboscis pore in the center of anterior sucker. Coloration of living animals: body almost transparent, light brown, with multiple yellowish pigment cells. Coloration of ethanol-preserved animals: dorsum beige to light brown, with darker broad inner paramedian lines and light yellowish areas laterally and anteriorly; ovate light yellow or white spots at each papillae on annulus a2 arranged into four longitudinal rows (outer paramedian and inner paramarginal), sometimes with a few white spots between them. Three pairs of ovate eyespots arranged to two parallel rows; in some specimens eyes on each side are joined to a single large spot. Venter whitish to light brown, sometimes with irregular brownish shading. Total number of annuli: 70. Somites I–III uniannulate, IV biannulate, V–XXIV triannulate, XXV biannulate, XXVII uniannulate. The male and female genital pores are separated by two annuli and are located in the furrows XIa3/XIIa1 and XIIa2/a3, respectively. Reproductive system: 6 pairs of spherical testisacs inter-segmentally from XIII/XIV to XVIII/XIX; atrium spherical, the atrial cornua large, twisted anteriorly; paired ejaculatory ducts very long, extending to XVIII; paired ovisacs massive, long, with multiple lobes, arranged as loops, extending to XVIII (pregnant specimen with eggs). Digestive system: proboscis sheath massive, thick, elongated; esophagus narrow; salivary glands diffuse; crop with 7 pairs of crop caeca: 1st-6th uniform, bag-like, 7th pair (posterior caeca) with 4 blind processes and several smaller lobes; intestine enlarged, with 4 pairs of large, long, bag-like processes, expanding distally, each with several short lobes; a large circular extension after the last pair of processes.
Distribution. Polar Urals (not known beyond the type locality).
Habitats and ecology. The type series of this species was collected from a natural mountain lake with stony bottom. The leeches were recorded beneath flat stones (Fig. 3b); their feeding behavior and life cycle remain unknown.
Glossiphonia taymyrensis Bolotov, Eliseeva, Klass & Kondakov sp. nov
Figures 4E, 5d, 7b, Supplementary Figs. S2h, S3c, S6, Supplementary Table S2.
LSID: https://zoobank.org/urn:lsid:zoobank.org:act:40269BF4-FE1C-4269-A7CC-41020789DC44.
Holotype. RMBH Hir_0258_1-H (sequenced: COI sequence acc. No. ON810695), RUSSIA: small lake near Dudinka on Taymyr Peninsula, 69.4008°N, 86.3384°E, July 16, 2018, O. V. Aksenova et al. leg.
Paratypes (N = 8). RUSSIA: 2 specimens RMBH Hir_0263_1 and RMBH Hir_0264_3 (sequenced: COI sequence acc. No. ON810701 and ON810705; 18S rRNA sequence acc. No. ON819017), the type locality, the same date, and collectors; 2 specimens RMBH Hir_0256_1 (one sequenced and one placed on 20 permanent slides as a series of slices; COI sequence acc. No. ON810693), small lake near Dudinka on Taymyr Peninsula, 69.3987° N, 86.3505° E, July 16, 2018, O. V. Aksenova et al. leg.; 1 specimen RMBH Hir_0261_2 (sequenced: COI sequence acc. No. ON810699; 18S rRNA sequence acc. No. ON819016), small lake near Dudinka on Taymyr Peninsula, 69.4014° N, 86.3250° E, July 16, 2018, O. V. Aksenova et al. leg.; 1 specimen RMBH Hir_0265_2 (sequenced: COI sequence acc. No. ON810706; 18S rRNA sequence acc. No. ON819021), Bolgokhtokh River near Dudinka, Taymyr Peninsula, 69.3780° N, 87.2215° E, July 21, 2018, O. V. Aksenova et al. leg.; 1 specimen RMBH Hir_0488 (sequenced: COI sequence acc. No. ON810755), a lake on Putorana Plateau, 68.7607° N, 91.9014° E, July, 2021, E. S. Chertoprud leg.; 1 specimen RMBH Hir_0449 (sequenced: COI sequence acc. No. ON810731), Pyzas River near Ust-Kabyrza settlement, 52.8277° N, 88.3973° E, Tashtagolsky District, Kemerovo Region, July 23, 2020, E. S. Babushkin & M. V. Vinarski leg.
Etymology. The new species is named after the Taymyr Peninsula, where the majority of the type specimens were collected.
Differential diagnosis. Small leech with broad, leaf-like, ovate body; three pairs of eyespots (distal pair joined; next two pairs separate); dorsal papillae absent; dorsal coloration with two inner paramedian rows of black spots, sometimes joining into unclear dashed lines; two annuli between the male (XIa3/XIIa1) and female (XIIa2/a3) genital pores. The new species largely resembles G. complanata but could be distinguished from it by having a smooth dorsum, without clear papillae. These taxa seem to have non-overlapping, allopatric ranges and, hence, could be separated on the basis of geographic criteria. However, the DNA approach seems to be the most appropriate way to distinguish these two species.
Molecular diagnosis. The new species represents a separate genetic lineage belonging to the complanata-group (Fig. 1). The pairwise COI p-distance of the new species from other congeners varies from 6.0 to 12.2%. The intraspecific pairwise COI p-distance ranges from 0.0 to 1.1% (mean ± s.e.m. = 0.52 ± 0.07%; N = 8 sequences and 28 pairwise distance values). The GenBank acc. numbers of reference DNA sequences (COI and 18S rRNA) are given in Supplementary Table S2 and Supplementary Datasets S1–S2.
Description. Small leech (body length up to 11.3 mm). Measurements of the type series are given in Supplementary Table S2. Body broad, leaf-like, ovate. Dorsum smooth, without clear papillae. Posterior sucker ovate (maximum diameter of 3.0 mm), ventrally directed. Proboscis pore in the center of anterior sucker. Coloration of living animals: not examined. Coloration of ethanol-preserved animals: (1) typical form having beige to light brown ground color without light spots but with darker brown coloration between inner paramedian lines; (2) melanic forms having dark brown ground color with four rows of large yellow spots (outer paramedian and marginal series) and yellow median stripe anteriorly (f. ‘maculosa’) or with strongly reduced yellow markings pattern. In all forms, there are two inner paramedian rows of black spots, sometimes joining into unclear dashed lines. Three pairs of ovate eyespots; the eyespots of the distal pair joined into a single spot; the eyespots of the next two pairs separate and are spaced apart. In the typical form, venter light yellow, with paired brown median and outer paramedian lines, which may be reduced to series of narrow brown longitudinal stripes. In melanic forms, ventral markings is more developed, with a series of brown longitudinal lines from median to inner paramarginal position and outer paramarginal brown spots. Posterior sucker with dense brown spots in melanic forms and with scarce brown spots in typical form. Total number of annuli: 68. Somites I–IV uniannulate, V–XXIV triannulate, XXV biannulate, XXVI–XXVII uniannulate. The male and female genital pores are separated by two annuli and are located in the furrows XIa3/XIIa1 and XIIa2/a3, respectively. Reproductive system: 6 pairs of spherical testisacs inter-segmentally from XII/XIII to XVIII/XIX; atrium ovate, the atrial cornua directed laterally; paired ejaculatory ducts twisted, short; paired ovisacs short, thick (undeveloped). Digestive system: salivary glands diffuse; proboscis sheath moderately thick; esophagus ovate; crop with 6 pairs of massive, bag-like, uniform crop caeca; intestine with 4 pairs of processes.
Distribution. Western and Eastern Siberia.
Habitats and ecology. The new species was recorded from natural lakes and rivers (Supplementary Dataset S2); its feeding behavior and life cycle are unknown.
Genus Hyperboreomyzon Bolotov, Eliseeva, Klass & Kondakov gen. nov
LSID: https://zoobank.org/urn:lsid:zoobank.org:act:298FF41E-AF0D-4442-9F82-3022B8094A67.
Type species: Hyperboreomyzon polaris gen. & sp. nov.
Etymology. This name is compiled using two Greek words: ‘Hyperborea’ (meaning a mythical far northern land) and ‘myzon’ (meaning sucking).
Diagnosis. Medium-sized, elongate, sub-fusiform glossiphoniid leeches; body and posterior sucker densely covered by shallow, ‘fish-scale’-like papillae; somite V biannulate; somites XII–XXIII secondarily sexannulate dorsally and ventrally due to the presence of very deep, prominent furrows separating each annulus to two semi-annuli; six rows of prominent dorsal tubercle-like papillae at a2 (inner paramedian, inner paramarginal, and marginal series) from V to XXVI; two pairs of circular eyespots on II and Va1 at inner paramedian position; gonopores at the furrows XIa3/XIIa1 (male) and XIIa2/a3 (female) and separated by two annuli; male atrium spherical; proboscis pore opens in a thick velar fold in the anterior half of oral sucker; one pair of compact, massive, elongated, incurved salivary glands, each gland with a bunch of a few short processes apically; 9 crop caeca pairs. Comparison of the new genus with other genera in the family based on morphological and anatomical features is presented in
Supplementary Table S3. Sexannulate condition was also recorded in the genus Actinobdella Moore, 1901 from North America36, but it differs from Hyperboreomyzon gen. nov. by having one pair of eyespots, diffuse salivary glands, and an apical position of proboscis pore (Supplementary Table S3).
Comments. This genus is established for a single species, which is described below.
Hyperboreomyzon polaris Bolotov, Eliseeva, Klass & Kondakov gen. & sp. nov.
Figures 4J, 5e, 6a-j, 7c, Supplementary Figs. S21, S8, S9, S10, S11, Supplementary Table S2.
LSID: https://zoobank.org/urn:lsid:zoobank.org:act:503A9A26-CEDE-4747-952D-8416AE4EF4EB.
Holotype. RMBH Hir_0486-H (sequenced: COI sequence acc. No. ON810753; 18S rRNA sequence acc. No. ON819030), RUSSIA: small alpine lake on Putorana Plateau, 68.9008°N, 94.1599°E, July, 2021, E. S. Chertoprud leg.
Paratypes (N = 2). RUSSIA: 1 specimen RMBH Hir_0689 (dissected and placed on 60 permanent slides as a series of slices), small alpine lake on Putorana Plateau, 68.6659° N, 93.1365° E, August 11, 2021, E. S. Chertoprud leg.; 1 specimen RMBH Hir_0216 (sequenced and dissected; COI sequence acc. No. ON810677; 18S rRNA sequence acc. No. ON819005), water puddle on Kolguev Island, 68.9300° N, 49.0303° E, August 12, 2018, O. V. Travina & V. M. Spitsyn leg.
Etymology. The name of the new species reflects its occurrences in polar (Arctic) areas of Eurasia.
Differential diagnosis. As for the genus.
Molecular diagnosis. None of congeneric species is known. Based on uncorrected pairwise COI p-distances between a haplotype of the new taxon and selected species-level haplotypes in each genus (Supplementary Table S1), Hyperboreomyzon seems to be more closely related to members of Hemiclepsis (mean distance ± s.e.m. = 11.62 ± 0.15%, range = 9.75–14.08%, N = 9) and Theromyzon (mean distance ± s.e.m. = 11.37 ± 0.07%, range = 10.47–12.64%, N = 9) without significant differences between distances from these two genera (Mann–Whitney test: p = 0.72). Other Glossiphoniidae genera are more distantly related, with a mean pairwise uncorrected COI p-distance of > 13.0% (Mann–Whitney test: p < 0.001) (Figure S14). In our two-locus phylogeny, it clusters with the Theromyzon and Placobdelloides clades but with moderate support (BS = 63) (Fig. 1). The intraspecific pairwise COI p-distance between two available sequences of this species is 0.3%. The GenBank acc. numbers of reference DNA sequences (COI and 18S rRNA) are given in Supplementary Table S2 and Supplementary Datasets S1–S2.
Description. Medium-sized leech (body length up to 20.6 mm). Measurements of the type series are given in Supplementary Table S2. Body massive, elongated, sub-fusiform, with rounded anterior and posterior ends, dorsum convex, venter slightly concave, lateral margins of the body slightly arched ventrally. The entire body densely covered by shallow, ‘fish-scale’-like papillae; dorsum with six rows of prominent tubercle-like papillae at a2 (inner paramedian) extending from V to XXVI. Lip small, rounded, with a deep median fold; proboscis pore opens in a massive velar fold in oral sucker close to its anterior margin; posterior sucker circular, small (maximum diameter of 3.4 mm), ventrally directed, dorsally covered by shallow, ‘fish-scale’-like papillae, similar to those on the body. Coloration of living animals: not examined. Coloration of ethanol-preserved animals: dorsum brown to dark brown, with a spotted coloration consisted of dense brown pigment cells; six rows of circular yellow to dark orange spots on each dorsal tubercle-like papilla (inner paramedian, inner paramarginal, and marginal; located on a2); two pairs of small, circular eyespots in inner paramedian position: the distal pair on II, the proximal pair on Va1. Venter light brown to brown, with a spotted coloration like that on the dorsum and with a light yellow median line. Posterior sucker light brown with dense dark brown spots, forming a reticulate pattern. Total number of annuli: 68. Somite I merged with prostomium; II–IV uniannulate, V biannulate and forms posterior margin of anterior sucker, VI–XXIV triannulate (XII–XXIII secondarily sexannulate dorsally and ventrally due to the presence of deep, prominent furrows separating each annulus to two semi-annuli), XXV–XXVI biannulate, XXVII uniannulate. The male and female genital pores are separated by two annuli and are located in the furrows XIa3/XIIa1 and XIIa2/a3, respectively. Reproductive system: 6 pairs of spherical testisacs inter-segmentally from XIII to XIX; male atrium spherical, the atrial cornua distinctly narrowed, elongated, slightly tapering distally, laterally directed; a prominent dumbbell-shaped patch of black tissue of unknown functionality at the dorsal surface of atrium in XII (between XIIa1 and a3); paired ejaculatory ducts narrow, long, extending to XIX; paired ovisacs massive, elongated, convoluted thin-walled structures, arranged as loops, extending from XII to XIV. Digestive system: proboscis sheath narrow, long; esophagus narrow; salivary cells aggregated to a pair of compact, massive, elongated, incurved glands in X, each gland bears a bunch of 2–3 short processes apically; crop with 9 pairs of crop caeca: 1st-8th uniform, 9th pair forms posterior caeca with 4 blind processes; intestine with 4 pairs of simple processes.
Distribution. Known from Kolguev Island and Putorana Plateau only.
Habitats and ecology. Three available specimens were collected from alpine lakes on the Putorana Plateau (altitude 426 and 524 m a.s.l.) and from a water puddle in plain tundra on the Kolguev Island (altitude 30 m a.s.l.). Feeding behavior, hosts, and life cycle are unknown.
Subfamily Theromyzinae Sawyer, 1986
Genus Theromyzon Philippi, 1867
Type species: Theromyzon pallens Philippi, 1867 (by monotypy).
Arctic occurrences. Two species in this genus are commonly occur in the Arctic, that is, Theromyzon maculosum (Rathke, 1862) and T. tessulatum (O. F. Müller, 1773).
Comments. Traditionally, nominal taxa in this genus were classified based on the number of annuli between gonopores15,42,43. This morphology-based concept is largely supported by our new DNA data. In particular, there are two phylogenetic species groups: (1) the maculosum-group with T. maculosum and a few related species from North America and the Caucasus Mountains (two annuli between gonopores); and (2) the tessulatum-group with T. tessulatum (four annuli) and T. mollissimum Grube, 1871 (five annuli). Foote et al.44 suggested that the number of annuli separating the gonopores can hardly be used as a species-level distinguishing feature for Nearctic members of the genus Theromyzon but, according to our combined two-locus phylogeny (COI + 18S rRNA), it seems to be a reliable character to separate taxa between the two species groups, mentioned above (Fig. 1).
The nominal taxon Placobdella raboti Blanchard, 1893 was described from the Scandinavian Arctic (type locality: ‘l’Ivalojoki, rivière tributaire du lac Enara, par 25° de longitude est et entre 68 et 69° de latitude nord (Laponie finlandaise)’ = Finland: Ivalo River, a tributary of Lake Inari, approx. 68.442° N, 25.000° E, Northern Lapland)13. Lukin15 considered it as a synonym of Placobdella costata (F. Müller, 1846). However, this issue is not so straightforward both morphologically and geographically. This species does not have a median row of papillae, which is a characteristic feature of Placobdella costata. Moreover, records of the latter (pond turtle-feeding) species north of the Arctic Circle are hardly expected. Based on genetically confirmed records, the northern portion of its range expands throughout northern Germany, Latvia, Ukraine, and Southern European Russia45. Briefly, the holotype (fixed by monotypy) of Placobdella raboti is a medium-sized ethanol-preserved specimen (body length 17 mm, body width 9.5 mm) of ovate shape, with small but deep posterior sucker (width 3 mm); proboscis pore opens on the rim of the anterior sucker (anterior lip); body thin, dorsal side convex, ventral side deeply concave; six rows of large dorsal papillae from somite XII to the last annuli, with marginal rows being smaller and less prominent; the edge of each a2 slightly rises apically, leading to a very particular scalloped aspect; body color uniformly grey-brown but with lighter ventral side and lighter dorsal papillae; one pair of eyespots; gonopores between two annuli; total number of annuli 6713. These features correspond well to a melanic form of Theromyzon maculosum (see Figs. 3g and 4i for such a form from Taymyr), except for the number of eyespots and annuli. If we assume that the eyespots and annulation were poorly recognizable in the heavily contracted holotype, Placobdella raboti may be considered a synonym of the latter species, because none of the other leech species in the Scandinavian Arctic shares a more or less similar combination of characters. Here, we would consider Placobdella raboti as a taxon inquirendum until more convincing evidence of its validity and taxonomic position is presented.
The nominal taxon Protoclepsis garjaewi Livanow, 1902 from Lake Baikal42 also corresponds morphologically to a melanic form of Theromyzon maculosum and may represent its synonym, as it was suggested previously15. Conversely, Theromyzon garjaewi groenlandicum Bennike, 1939 from West Greenland (type locality: Lake Ferguson, Søndre Strømfjord, 66.9667° N, 50.6333° W)10,46,47 may represent a separate Nearctic species of the maculosum-group, because the presence of the Palearctic T. maculosum in North America was not confirmed43. However, the status of this nominal taxon is still uncertain due to the lack of DNA sequence data. There are three more Nearctic species with two annuli between the gonopores, i.e. T. rude (Baird, 1869), T. bifarium Oosthuizen & Davies, 199343, and T. tigris Foote et al., 202244.
The nominal taxon Protoclepsis meyeri Livanow, 1902 was described based on syntypes from European Russia (Kazan city, Republic of Tatarstan)42. Livanow42 stated that ‘‘Unter den Protoclepsis-Arten wird Protoclepsis maculosa in die Nähe von Protoclepsis meyeri zu stellen sein, mit welcher sie in ihrer Organisation durchaus übereinstimmt, so dass beide vielleicht bloss Varietäten ein und derselben Art bilden’’ (p. 358). Based on the original description42, Protoclepsis meyeri was established on the basis of typical yellow-spotted specimens of Theromyzon maculosum and, according to Lukin15 and Nesemann and Neubert10, should be considered its synonym.
Subfamily Haementeriinae Autrum, 1939
Genus Helobdella Blanchard, 1896
Type species: Helobdella stagnalis (Linnaeus, 1758) (= Hirudo stagnalis Linnaeus, 1758; by original designation).
Arctic occurrences. Two allopatric species in this genus were recorded north of the Arctic Circle: Helobdella stagnalis and one species new to science, which is described below (Table 1).
Comments. The nominal species Placobdella guernei Blanchard, 1893 was described from Arctic Norway (type locality: ‘Gadde Luobal, dans le Pasvig, environ par 69° 20′ latitude nord et 27° 30′ longitude est’ = Norway: Lake Gåddeluobbal, Paatsjoki/Pasvik River basin, 69.2583° N, 29.0804° E) on the basis of a small specimen (7 mm long, 3 mm wide) with poorly developed external features13. Previously, it was linked to Placobdella costata15 or to Helobdella stagnalis48. Based on the original description13, we agree with the latter point of view. In particular, Blanchard13 noted that the holotype (fixed by monotypy) is a bioculate specimen with smooth (non-papillated) body, having two very wide preocular annuli, a wide annulus with eyespots, and narrower annuli afterwards. This patterns clearly corresponds to the arrangement of annuli and eyespots on the head region of Helobdella stagnalis (Supplementary Fig. S2k). Blanchard13 did not mention the presence of the dorsal nuchal scute but some aberrant individuals of Helobdella stagnalis may lack this feature15. Here, we would consider Placobdella guernei as a taxon inquirendum until a more convincing proof of its validity and taxonomic placement is presented.
Helobdella okhotica Bolotov, Eliseeva, Klass & Kondakov sp. nov
= Helobdella stagnalis Lukin (1976): 10225 (identification error).
Figures 4l, 5f, 7d, Supplementary Figs. S2j, S3d, S7, Supplementary Table S2.
LSID: https://zoobank.org/urn:lsid:zoobank.org:act:EBA26356-E4C4-4D51-888E-EAB7516457A8.
Holotype. RMBH Hir_0251_1-H (non-sequenced), RUSSIA: Khodeevskoye Lake, 64.7501° N, 177.7771° E, Chukotka Peninsula, July 27, 2019, O. V. Aksenova, A. V. Kondakov & I. V. Vikhrev leg.
Paratypes (N = 11). RUSSIA: 3 specimens Hir_0251_1 (one sequenced: COI sequence acc. No. ON810688; 18S rRNA sequence acc. No. ON819009), the type locality, the same date, and collectors; 3 specimens RMBH Hir_0003_2 (one sequenced: COI sequence acc. No. MN393255), Tumnin River, 49.9451° N, 139.9181° E, Khabarovsk Region, July 14, 2014, I. N. Bolotov & I. V. Vikhrev leg.; 1 specimen RMBH Hir_0294 (sequenced: COI sequence acc. No. ON810719), Azabache Lake, 56.1521° N, 161.8561° E, Kamchatka River basin, Kamchatka Peninsula, August 6, 2019, O. V. Aksenova, S. E. Sokolova & A. R. Shevchenko leg.; 3 specimens RMBH Hir_0295 (one sequenced: COI sequence acc. No. ON810720), Krasikovskoye Lake, 56.2411° N, 162.0250° E, Kamchatka River basin, Kamchatka Peninsula, August 8, 2019, O. V. Aksenova, S. E. Sokolova & A. R. Shevchenko leg.; 1 specimen RMBH Hir_0491_1 (placed on 34 permanent slides as a series of slices), an unnamed small lake near Kurazhechnoe Lake, 56.3380° N, 160.8479° E, Kamchatka River basin, Kamchatka Peninsula, September 9, 2021, A. V. Kondakov leg.
Etymology. The new species is named after the Sea of Okhotsk, because it is widely distributed in freshwater basins, emptying into this sea.
Differential diagnosis. Small leech with elongated body; one pair of eyespots; dorsal papillae, tubercles, and dark markings absent; ovate dorsal nuchal scute at VIII a2/a3; one annulus between the male (XIIa1/a2) and female (XIIa2/a3) genital pores. The new species is morphologically similar to H. stagnalis and can reliably be distinguished from it by means of the DNA approach only. However, the new species seems to have a smaller dorsal nuchal scute compared with that of H. stagnalis. Furthermore, the two species have allopatric ranges and could also be delineated geographically. Helobdella nuda (Moore, 1924), which rarely occurs in the Russian Far East and Eastern Siberia15,49, differs from the new species by having two pairs of eyespots and by the total lack of dorsal nuchal scute.
Molecular diagnosis. Genetically, the new species is most closely related to H. stagnalis and H. sp. ‘Korea’ (mean uncorrected pairwise COI p-distance = 6.9 and 3.8%, respectively). The intraspecific pairwise COI p-distance ranges from 0.0 to 2.3% (mean ± s.e.m. = 1.24 ± 0.09%; N = 11 sequences and 55 pairwise distance values). The GenBank acc. numbers of reference DNA sequences (COI and 18S rRNA) are given in Supplementary Table S2 and Supplementary Datasets S1-S2.
Description. Small leech (body length up to 7.7 mm). Measurements of the type series are given in Supplementary Table S2. Body elongated, with triangular anterior end and ovate dorsal nuchal scute at VIII a2/a3 (furrow between annuli 12 and 13). Dorsum without papillae and tubercles. Posterior sucker circular (maximum diameter of 1.6 mm), ventrally directed, without pigmentation. Proboscis pore in the center of anterior sucker. Coloration of living animals: not examined. Coloration of ethanol-preserved animals: dorsum and venter white, without pigmentation. One pair of circular eyespots. Total number of annuli: 67. Somites I–III uniannulate, IV–V biannulate, VI–XXIII triannulate, XXIV–XXV biannulate, XXVI–XXVII uniannulate. The male and female genital pores are separated by one annulus and are located in the furrows XIIa1/a2 and XIIa2/a3, respectively. Reproductive system: 6 pairs of large, elliptical testisacs arranged intra-segmentally from XIV to XIX; atrium small, spherical, the atrial cornua ovate, elongated, laterally directed; paired ejaculatory ducts short; paired ovisacs massive, with several blind lobes, extending from XII to XVI. Digestive system: proboscis sheath rather narrow, very long, J-shaped distally; esophagus narrow, S-shaped; one pair of diffuse salivary glands; crop with 5 pairs of crop caeca: 1st-4th uniform, 5th pair forms uniform posterior caeca; intestine with 4 pairs of long, simple processes and a bag-like extention after the last pair of processes.
Distribution. Eastern Siberia (Lena River basin) and Russian Far East (Chukotka, Kamchatka, Kolyma Highland, Khabarovsk Region, Primorye, and Amur Region).
Habitats and ecology. This species was recorded from a wide array of water bodies such as rivers, lakes, reservoirs, and even a water puddle (Supplementary Dataset S2); its feeding behavior and life cycle are unknown.
Source: Ecology - nature.com
