REVISION OF SANGUINICOLA PLEHN, 1905 WITH REDESCRIPTION OF SANGUINICOLA VOLGENSIS (RAŠÍN, 1929) MCINTOSH, 1934, DESCRIPTION OF A NEW SPECIES, PROPOSAL OF A NEW GENUS, AND PHYLOGENETIC ANALYSIS

Sanguinicola Plehn, 1905 is a neglected genus of blood fluke that got off to a bad start (Bullard et al., 2009; Warren and Bullard, in press). Plehn (1905) assigned Sanguinicola armata Plehn, 1905 (type species) and Sanguinicola inermis Plehn, 1905 (see Plehn, 1905) to the Turbellaria and then to a group of monozoic cestodes (Plehn, 1908; Bullard et al., 2009). These species were redescribed by Ejsmont (1926) with a level of thoroughness unmatched by some current blood fluke descriptions. No researcher has conducted anatomical work as detailed as that of Ejsmont (1926) on a species of Sanguinicola and addressed the obvious systematic issues with the genus. Plehn (1905) assigned the markedly morphologically distinct species, S. armata and S. inermis, to the same genus. Ejsmont (1926) accepted this assignment in his redescription of S. armata and S. inermis. Until 2008, all freshwater fish blood flukes were assigned to Sanguinicola, except for Plehniella coelomicola Szidat, 1951 and Paracardicoloides yamagutii Martin, 1974 (see Szidat, 1951; Martin, 1974). Disregarding the obvious, stark morphological and ecological differences between the genera, Yamaguti (1958) synonymized Plehniella Szidat, 1951 with Sanguinicola (see Orélis-Ribeiro and Bullard, 2015). Subsequently, Madhavi and Hanumantha Rao (1970) and Smith (1972, 1997a, 1997b, 2002) accepted this synonymy. Since 2007, 5 freshwater fish blood fluke species assigned to 4 genera and from 3 continents (Asia, North America, South America) have been described (Acipensericola petersoni Bullard, Snyder, Jensen, and Overstreet, 2008; Nomasanguinicola canthoensis Truong and Bullard, 2013; Cladocaecum tomasscholzi Orélis-Ribeiro and Bullard, 2016; Kritsky platyrhynchi Orélis-Ribeiro and Bullard, 2016; Acipensericola glacialis Warren and Bullard, 2017). Additionally, 2 new species of Plehniella were described and the genus was resurrected and revised (Plehniella sabajperezi Orélis-Ribeiro and Bullard, 2015; Plehniella armbrusteri Orélis-Ribeiro and Bullard, 2016). Sanguinicola remains in need of revision. It comprises 26 nominal species that collectively infect fishes assigned to 8 orders (Cypriniformes, Characiformes, Siluriformes, Esociformes, Salmoniformes, Labriformes, Centrarchiformes, Perciformes) (Smith, 1997a, 1997b) (Tables I, II). It is the most speciose of the 7 freshwater fish blood fluke genera (Sanguinicola; Plehniella; Paracardicoloides Martin, 1974; Acipensericola Bullard, Snyder, Jensen, and Overstreet, 2008; Nomasanguinicola Truong and Bullard, 2013; Cladocaecum Orélis-Ribeiro and Bullard, 2016; Kritsky Orélis-Ribeiro and Bullard, 2016).

Herein, using newly collected material from North America and Russia, we emend Sanguinicola; describe a new species infecting northern pike, Esox lucius Linnaeus, 1758; redescribe Sanguinicola volgensis (Rašín, 1929) McIntosh, 1934 (see Rašín, 1929) infecting the type host, sabrefish, Pelecus cultratus (Linnaeus, 1758) Berg, 1949; describe an innominate species of Sanguinicola infecting ide, Leuciscus idus (Linnaeus, 1758) Berg, 1949; and propose a new genus infecting walleye, Sander vitreus (Mitchill, 1818) Bailey, Latta, and Smith, 2004 in North America. We also use the large subunit ribosomal DNA (28S) to explore their relationships with the other blood fluke lineages.

Fish blood flukes were collected during 2020–2021 from the heart of walleye (S. vitreus; Oneida Lake, New York and Fox River, Wisconsin), sabrefish (P. cultratus; Upper Volga River, Russia), ide (L. idus; Upper Volga River, Russia), and northern pike (E. lucius; Upper Volga River, Russia). The heart was excised intact, placed in a sample bag (heart bisected), exposed to 70 C fresh water, shaken vigorously, and fixed in 5–10% neutral buffered formalin (n.b.f.). In the laboratory, each heart was examined with the aid of a dissecting microscope and fiber optic light source to isolate flukes. The heart was teased apart with forceps to reveal adult blood flukes, and sediment from the fixed heart was taken from a settling column and examined. Adult specimens collected for DNA extraction were wet mounted on glass slides and examined to confirm their identity, preserved in 95% ethanol (EtOH), and stored at −20 C. Adult flukes (n = 15) fixed in formalin and intended for morphology were rinsed with distilled water, cleaned with fine brushes to remove any debris, stained overnight in Van Cleave’s hematoxylin with 3 additional drops of Ehrlich’s hematoxylin, dehydrated using an ethanol series, cleared in clove oil, permanently mounted in Canada balsam, illustrated using an Olympus BX51 microscope (Olympus Corporation of the Americas, Center Valley, Pennsylvania) equipped with differential interference contrast (DIC), measured using an ocular micrometer, and illustrated using a drawing tube. Methods for electron microscopy are from Poddubnaya et al. (2023). Measurements are reported in micrometers (μm) as the range followed by the mean, standard deviation, and sample size in parentheses unless otherwise indicated. Scientific names, including taxonomic authorities and dates, for fishes follow Eschmeyer et al. (2016; online version updated 2022). Classification and anatomical terms for fish blood flukes follow Bullard (2010), Bullard et al. (2012), and Warren et al. (2019, 2021). Types and vouchers were deposited in the National Museum of Natural History’s Invertebrate Zoology Collection (USNM, Smithsonian Institution, Washington, DC).

A total of 8 EtOH-preserved and microscopically identified fish blood flukes were used for DNA extraction and sequencing: 2 specimens from walleye, S. vitreus (Perciformes: Percidae), 2 from sabrefish, P. cultratus (Cypriniformes: Leuciscidae), 2 from ide, L. idus (Cypriniformes: Leuciscidae), and 2 from northern pike, E. lucius (Esociformes: Esocidae). Total genomic DNA (gDNA) was extracted using DNeasyTM Blood and Tissue Kit (Qiagen, Valencia, California, USA) as per the manufacturer’s protocol, except that the proteinase-K incubation period was extended overnight, and the final elution step used 100 microliter (μl) of elution buffer to increase the final DNA concentration. The 28S was amplified using primers outlined in Warren et al. (2021). PCR amplifications were performed with the cycling profile identified by Warren et al. (2017b), except that the annealing temperature was set at 56 C for 30 sec. PCR reactions were carried out in a MJ Research PTC-200 (BioRad, Hercules, California). PCR products (12 μl) were verified on a 1% agarose gel and stained with ethidium bromide. PCR products were purified by microcentrifugation with the QIAquick PCR Purification Kit (Qiagen, Valencia, California) according to the manufacturer’s protocols, except that the last elution step was performed with autoclaved nanopure H₂O rather than with the provided buffer. DNA sequencing was performed by Genewiz (South Plainfield, New Jersey). Sequence assembly and analysis of chromatograms were performed with Geneious version 2022.0.2 (http://www.geneious.com). Nucleotide sequence data were deposited in GenBank (Table III).

The phylogenetic analyses included the new freshwater fish blood fluke sequences and selected sequences representing species of fish blood flukes that were available on GenBank (Table III). The outgroup is represented by the turtle blood flukes Baracktrema obamai Roberts, Platt, and Bullard, 2016, Spirorchis artericola (Ward, 1921) Stunkard, 1921, and Vasotrema robustum for the analysis (Table III). The turtle blood fluke sequences have been recovered repeatably as a sister taxon to the fish blood flukes (Olson et al., 2003; Orélis-Ribeiro et al., 2014). Sequences were aligned with the multiple alignment tool using fast Fourier transform (MAFFT) (Katoh and Standley, 2013) and trimmed to the length of the shortest sequence presented herein (1,362 [28S] base pairs [bp]). JModelTest 2 version 2.1.10 (Darriba et al., 2012) was implemented to perform a statistical selection of the best-fit models of nucleotide substitution based on Bayesian information criterion (BIC). Aligned sequences were reformatted (from .fasta to .nexus) using the web application ALTER (Glez-Peña et al., 2010) to run Bayesian inference (BI). BI was performed in MrBayes version 3.2.5 (Ronquist and Huelsenbeck, 2003) using substitution model averaging (“nst-mixed”) and a gamma distribution to model rate heterogeneity. Defaults were used in all other parameters. 3 independent runs with 4 Metropolis-coupled chains were run for 5,000,000 generations, sampling the posterior distribution every 1,000 generations. Convergence was checked using Tracer v1.6.1 (Rambaut et al., 2014) and the “sump” command in MrBayes: all runs appeared to reach convergence after discarding the first 25% of generations as burn-in. A majority rule consensus tree of the post burn-in posterior distribution was generated with the “sumt” command in MrBayes. The inferred phylogenetic tree was visualized using FigTree v1.4.4 (Rambaut et al., 2014) and further edited for visualization purposes with Adobe Illustrator (Adobe Systems).

Sanguinicola Plehn, 1905 , emended
(Figs. 1–17)

Body of adult <9× longer than wide, dorsoventrally flattened, lacking posterolateral protuberance, tapering equally anteriorly and posteriorly, spined; tegumental spines straight and not distally recurved, deeply rooted in tegument and only slightly protruding from it, arranging in a single column along lateral body margin, orienting laterally or slightly posterolaterally. Rose-thorn–shaped spines absent. Ventrolateral nerve cords and dorsolateral nerve cords present; ventrolateral nerve cord extending nearly entire body length, appearing slightly subterminal, with commissure anteriorly. Anterior body extremity proboscislike, accommodating mouth; mouth medioventral, subterminal, with associated toothlike mouth apparatus (Figs. 4I, 12B). Pharynx present. Esophagus medial, straight, not looping, extending posteriad less than one-fourth to one-third body length, with anterior and posterior esophageal swellings, with esophageal sunken glandular cells enveloping middle and posterior portion of esophagus, connecting with ceca, anteromedially. Intestine thin walled, medial, comprising 4–5 radial ceca that collectively appear generally as an X-shaped structure; each cecum can be dendritic. Testis single, having an array of lateral lobes, as wide or slightly wider than breadth of intestine, appearing as multiple testes distributing in 2 tandem rows flanking midline from level of ceca to posterior third or posterior quarter of body; middle testicular lumen extending along entire length of testis; sperm duct (vas deferens) single, arising from posterior middle regions of testis; spermatozoa having 9 + 0 axoneme pattern. Cirrus sac surrounding seminal vesicle, inconspicuous in some whole mounts, prostatic glands present. Male genital pore dextral, slightly lateral to midline. Ovary single, medial, with superficially lobed margins, with lateral portions extending anteriad and lateral to posterior portion of testicular field, appearing butterfly-wing shaped to varying degrees, as wide or wider than testicular field, occupying posterior one-third of body. Vitelline cells widely distributed throughout space from approximant level of anterior nerve commissure to seminal vesicle and mixed with other cell types comprising diffuse follicles. Oviduct a narrow duct extending directly posteriad from posteromedial surface of ovary, connecting with distal portion of vitelline reservoir to or near level of male genital pore; oviducal seminal receptacle present or absent. Ovovitelline duct connecting with oötype posteriorly or extending laterad and connecting to anterior aspect of oötype. Oötype compact, oblong, posterior to level of male genital pore, posterior to gonads and genital ducts. Laurer’s canal absent. Uterus short, not coiled, postovarian; uterine seminal receptacle lacking; uterine eggs triangular or ovoid; triangular eggs bearing a midbody stublike extension. Female genital pore anteromedial to male genital pore. Excretory vesicle appearing V-shaped or Y-shaped or diminutive; excretory pore terminal. Undergoing asexual reproduction in hydrobiid, semisulcospirid, planorbid, pleurocerid, lymnaeid, and valvatid snails (Warren and Bullard, in press); maturing in blood vascular system of Cypriniformes and Esociformes (Table I).

Body <9× longer than wide; lateral tegumental spines straight (not recurved), deeply rooted in tegument or slightly protruding from it, arranging in a single column along lateral body margin, orienting laterally or slightly posterolaterally. Intestine thin walled, medial, comprising 4–5 radial ceca that collectively appear generally as an X-shaped structure; each cecum can be dendritic, terminating in anterior half of the body. Testis single, having an array of lateral lobes, as wide or slightly wider than breadth of intestine, appearing as if multiple testes distributing in 2 tandem rows flanking midline from level of ceca to posterior third or posterior quarter of body. Male genital pore lateral to female genital pore, ending along midline. Ovary butterfly-wing shaped, postcecal, posttesticular. Oötype posterior to genitalia. Uterus short, not coiled. Eggs triangular or ovoid.

Sanguinicola armata Plehn, 1905 (ex. heart lumen of tench, Tinca tinca [Linnaeus, 1758] Berg, 1949 [Cypriniformes: Tinicidae] [type host] from Freising, Germany [type locality]).

Janickia Rašín, 1929.

Sanguinicola intermedia Ejsmont, 1926; Sanguinicola volgensis (Rašín, 1929) McIntosh, 1934,; Sanguinicola lophophora Erickson and Wallace, 1959; Sanguinicola skjabini Akhmerov, 1960; Sanguinicola magnus Hu, Long, and Lee, 1965; Sanguinicola lungensis Tang and Lin, 1975; Sanguinicola rhodei Wang, 1983; Sanguinicola rutili Simón-Martín, Rojo-Vásquez, and Simón-Vicente, 1988; Sanguinicola hasegawai Shimazu, 2013 (Table I).

Sanguinicola inermis Plehn, 1905; Sanguinicola chalmersi Odhner, 1924; Sanguinicola huronis Fischthal, 1949; Sanguinicola argentinensis Szidat, 1951; Sanguinicola davisi Wales, 1958; Sanguinicola klamathensis Wales, 1958; Sanguinicola alseae (Meade and Pratt, 1965) Holmes, 1971; Sanguinicola idahoensis Schell, 1974; Sanguinicola sanliense Wang, 1982; Sanguinicola clarias Imam, Marzouk, Hassan, and Itman, 1984; Sanguinicola fontinalis Hoffman, Fried, and Harvey, 1985; Sanguinicola maritimus Nolan and Cribb, 2005; Sanguinicola ugui Shimazu, 2007 (Table II).

Sanguinicola incognita Akhmerov, 1959; Sanguinicola shantsuensis Lung and Shen, 1965; Sanguinicola megalobramae Li, 1980 (Table II).

The revised diagnosis herein includes several additional taxonomic characters and further details of other features used to differentiate Sanguinicola sensu stricto (Table I) from other fish blood fluke genera. The diagnosis has been emended several times (Ejsmont, 1926; Yamaguti, 1958; Smith, 2002), but several useful characters and details have been left out or ignored. Specifically, lateral tegumental spines are present in Sanguinicola spp.; no accepted species of Sanguinicola lacks spines. Sanguinicola has a single column of spines and lacks transverse rows of spines; with each spine being straight and lacking a recurved tip. We detail the position and shape of the nerve cords, mouth, esophagus, intestinal ceca, testis, vasa deferens, vitelline distribution, ovary, oviducal seminal receptacle, oötype, genital pores, excretory vesicle, and uterus.

Sanguinicola sensu stricto (Table I), as revised herein, is most similar to monotypic Nomasanguinicola, which infects a bighead catfish, Clarias macrocephalus Günther, 1864 (Siluriformes: Clariidae) in the Mekong River, Vietnam, and monotypic Parasanguinicola Herbert and Shaharom-Harrison, 1995 (see Herbert and Shaharom-Harrison, 1995), which infects a sea bass (Perciformes: Latidae) in Malaysia. It differs from N. canthoensis most notably by lacking denticles flanking the mouth (not to be confused with minute concentric rows of spines). Further, N. canthoensis differs by having a uterus with ascending and descending portions (appearing as an inverse U-shape) as well as by lacking lateral tegumental spines (Truong and Bullard, 2013). Parasanguinicola vastispina Herbert and Shaharom-Harrison, 1995 (see Herbert and Shaharom-Harrison, 1995) differs by the number of spines along the tegument (<90), having lateral tegumental spines without a tegumental conical protrusion, a testis lacking lateral lobes, and (reportedly) a preovarian female genital pore (Herbert and Shaharom-Harrison, 1995). The location of the female genital pore needs confirmation. The position of the female genital pore in the illustration provided by Herbert and Shaharom-Harrison (1995) resembles the vitelline collecting duct and not an anteriorly extending uterus. We think that Herbert and Shaharom-Harrison (1995) mistook the proximal portion of the vitelline collecting duct as the distal portion of the uterus (Fig. 2, Herbert and Shaharom-Harrison, 1995). No other species of Sanguinicola has a preovarian genital pore.

The other freshwater fish blood fluke genera (Acipensericola, Plehniella, monotypic Cladocecum, monotypic Kritsky) differ from Sanguinicola by features associated with the anterior sucker, lateral tegumental spines, intestine, and genitalia. Species of Acipensericola, which infect sturgeons and paddlefish (Appy and Dadswell, 1978; Bullard et al., 2008; Orélis-Ribeiro and Bullard, 2015; Warren et al., 2017b), differ from Sanguinicola by having a large, pedunculate, bowl-shaped anterior sucker, lateral tegumental spines in transverse rows, an inverse U-shaped intestine, and a testicular column with 6 testes (including a postgenital testis) (Bullard et al., 2008; Warren et al., 2017b). Plehniella, monotypic Cladocecum, and monotypic Krtisky comprise species that infect catfishes only (Orélis-Ribeiro and Bullard, 2015). Plehniella spp. and Kritsky platyrhynchi (Guidelli, Isaac, and Pavanelli, 2002) Orélis-Ribeiro and Bullard, 2016 infect the body cavity but differ from Sanguinicola spp. by having an intestine comprising 6 radial ceca, a genital atrium, and a vas deferens that traverses anterior to the uterus (Orélis-Ribeiro and Bullard, 2015, 2016). Unique among fish blood flukes, Cladocecum tomasscholzi Orélis-Ribeiro and Bullard, 2016 has 1 pair of elongate anterior ceca plus a medial cecum with numerous branches extending laterad (Orélis-Ribeiro and Bullard, 2016).

We accept 10 species of Sanguinicola: S. armata, S. hasegawai, S. intermedia, S. lophophora, S. lungensis, S. magnus, S. skjabini, S. rhodei, S. rutili, and S. volgensis (Table I). These species differ from the actinopterygian blood flukes by having lateral tegumental spines that are not distally recurved and that are arranged in a single column (vs. lateral transverse rows of spines) (Bullard and Overstreet, 2003), an intestine comprising radial ceca (vs. long anterior and posterior ceca) (Bullard, 2013; Warren et al., 2021), and a single testis with lateral lobes extending from a massive seminal column (vs. a large testicular mass with vasa efferentia as an interconnected meshwork of ducts or multiple testes) (Bullard et al., 2012; Warren et al., 2021). Further, all blood flukes infecting chondrichthyans differ from Sanguinicola spp. by having a Laurer’s canal. They further differ by having C-shaped lateral tegumental spines and a non-sinusoidal testis or lacking spines and having a sinusoidal testis (Warren et al., 2019; Warren and Bullard, 2021).

A total of 16 species originally assigned to Sanguinicola need additional investigation regarding the lateral tegumental body spines, oral sucker spines, testis, and ovary to assign them to a genus confidently (Table II). Sanguinicola alseae, S. davisi, S. fontinalis, S. idahoensis, S. klamathensis, S. maritimus, S. occidentalis, and S. ugui have transverse rows or tufts (S. fontinalis) of spines (vs. a single column of large spikelike spines), and all are reported from North America except S. maritimus and S. ugui. Sanguinicola maritimus infects marine fishes in Australia (Nolan and Cribb, 2005; Shimazu, 2007). Sanguinicola inermis, S. huronis, and S. argentinensis were described as lacking lateral tegumental body spines (Ejsmont, 1926; Fischthal, 1949; Szidat, 1951). Further, S. inermis and S. argentinensis were described as having “bristles” distributed along the lateral body surface (Ejsmont, 1926; Szidat, 1951) but we speculate that these “bristles” could be sensory cilia, not spines (Fig. 4C–E). Moreover, S. alseae, S. davisi, S. idahoensis, and S. klamathensis, all of which infect North American salmoniforms, have an anterior “proboscislike” sucker with circumoral spines. This spine distribution is like those observed in several marine lineages of fish blood flukes (Elaphrobates euzeti Bullard and Overstreet, 2003) (Wales, 1958; Holmes, 1971; Schell, 1974; Bullard and Overstreet, 2003). Sanguinicola clarias differs from Sanguinicola spp. by having 4 denticles (described as rose-thorn spines) that flank the mouth and a uterus that is inverse U-shaped (Imam et al., 1984). Truong and Bullard (2013) suggested that this species and Plehniella dentata Paperna, 1964 should be reassigned to Nomasanguinicola because they have 2 columns of denticles flanking the mouth and other key features of the genus (Table II) (Paperna, 1964; Truong and Bullard 2013). We herein reassign them as Nomasanguinicola clarias (Imam, Marzouk, Hassan, and Itman, 1984) Warren and Bullard n. comb. and Nomasanguinicola dentata (Paperna, 1964) Warren and Bullard n. comb. Imam et al. (1984) included supplemental observations of S. chalmersi, which has a column of 7 denticles on each side of the mouth (Odhner, 1924; Imam et al., 1984); perhaps suggesting that a new genus is warranted for this taxon (Truong and Bullard, 2013). Finally, we consider S. incognita, S. megalobramae, and S. shantsuensis as nomina nuda because no description or illustration for these names could be found.

We propose several reasons for the lack of new information on Sanguinicola spp. First, specimens of Sanguinicola deteriorate extremely rapidly. We have observed that within an hour of euthanizing a fish host, the blood flukes are nonmotile, evidently dead, and seemingly deteriorated. Moreover, these flukes are exceptionally minute, delicate, and difficult to stain. Even with stains that work well for other blood flukes, we have observed that specimens of Sanguinicola appear to lose stain or never take it up to begin with. We suspect that the exceptionally poor condition of deposited types and vouchers of Sanguinicola spp. are at least in part explained by these methodological challenges; certainly, the extant types of Sanguinicola spp. are of limited value and are simply poor specimens. Additionally, whereas few parasitologists examine freshwater fishes for parasites (Scholz and Choudhury, 2014), even fewer examine them for blood fluke infections. Hence, we think many infections go undetected. Finally, because so many nominal species descriptions are diagrammatical or incomplete, the taxonomist has little to go on when differentiating newly collected specimens.

Sanguinicola plehnae Warren and Bullard n. sp.
(Figs. 1–4)

USNM collection no. 1688209): Body flat, ventrally concave, tapering posteriorly and anteriorly, 1,200–3,000 (2,100) long, 350–550 (450) at greatest width, 4.2× longer than wide (Figs. 1, 4B). Tegumental body spines 10–22 (16) from anterior end (Figs. 1, 4H), 5–7 (6) between spines anteriorly and 13–15 (14) posterior two-thirds of body (Figs. 2, 4G), 13 long, 2 wide at base, 6.4× longer than wide; distal region of spines projecting 2–3 (2.5) through tegument, best observed with SEM (Figs. 2, 4A, C–E, G); area surround protruding spines flattened, smooth, tegumental layer surrounded by a gathering of ciliated sensory endings (Fig. 4C–E, L), tegumental spines extending to level of oötype in posterior half, 215 from posterior end (Fig. 1), with 120 and 122 per side or total of 242 (95–97 visible with SEM) (Fig. 1). Anterior body extremity proboscislike, small, 10 long, 25 wide; spines absent. Mouth terminal, 1 long, 2 wide, possessing tegumental elevations into mouth cavity (Fig. 4H, I). Pharynx present. Ventrolateral nerve cord length indistinct, 11 wide near midbody at widest level, 78 from body margin. Nerve commissure perpendicular to midline of body, connecting ventrolateral nerve cords, 233 or 11% of body length from anterior end of body, 90 or 18% of body width across width of worm, 9 in breadth; secondary commissure branches 10 in maximum width. Esophagus 636 in total length or 30% of body length, 18 in maximum width (at level just anterior to nerve commissure), extending sinuously posteriad along midline, widening slightly posteriorly (Fig. 1). Esophageal sunken glandular cells present in the middle and posterior esophagus. Intestine thin walled, medial, comprising 4 radial ceca, X-shaped (Fig. 1); cecal intersection of anterior and posterior ceca 584 or 27% of body length from anterior body end; anterior ceca 54 long or 2.5% of body length, 23 wide, ventral to lateral nerve cord, containing granular material within lumen of some individuals (Fig. 1); posterior ceca asymmetrical, 72 long or 3% of body length, 25 wide, ventral to testis; postcecal space 1,479 long or 69% of body length.

Testis 876 long or 41% of body length, 208 wide or 41% of body width, 4.2× longer than wide, postcecal; testicular lobes irregular, not paired, extending laterally, 119 in length towards body margin (Figs. 1, 3); testicular central column large, resembling a column throughout the length of the testis, 26 wide (Figs. 1, 3). Posttesticular space 562 long or 26% of body length. Vas deferens 196 long, 13 wide, emanating from middle posteroventral portion of testis, following midline before become confluent with seminal vesicle. Cirrus sac present, having wall approximately 4 thick, including seminal vesicle, ejaculatory duct, and cirrus; seminal vesicle 184 long, 39 wide, 4.7× longer then wide (Figs. 1, 3); everted cirrus 10 long; male genital pore towards midline, postovarian, sinistral to female genital pore, 204 or 10% of body length from posterior body end (Fig. 4F).

Ovary medial, double winged in shape, appearing as loose aggregation of cells, 190 in maximum length or 9% of body length, 159 wide or 32% of body width, immediately posttesticular; postovarian space 399 long or 19% of body length (Figs. 1, 3). Oviduct 302 long or 14% of body length; oviducal seminal receptacle indistinct. Oötype 51 long, 49 wide; 159 long or 7% of body length from posterior end (Fig. 3). Vitellarium appearing as loose follicles, occupying space dorsal and lateral to testis and ceca, extending from nerve commissure to ovary (Fig. 1); common collecting duct 447 long, 14 wide. Uterus short, extending directly anteriad from oötype, 53 long, 32 wide (Fig. 3). Female genital pore medial, postovarian, lateral to seminal vesicle, 224 or 10% of body length from posterior body end (Figs. 3, 4F); 40 from male genital pore (Fig. 3). Excretory vesicle small, 30 long, 9 wide, medial.

The presence of irregular depressions and prominences of different size and shape were revealed on the surface of the distal tegumental cytoplasmic layer of the worms via SEM and TEM observations (Fig. 4J, K). The cytoplasmic matrix of this layer is moderately dense and contains a high concentration of rounded or ovoid dense granules 0.2–0.4 (0.3) μm in diameter and electron-lucent vesicles (Fig. 4K). Detailed description of ultrastructure features of spines, tegument, and sensory receptors of S. plehnae (see Poddubnaya et al., 2020). This taxon is the same species as that referred to as S. inermis in this previously mentioned paper.

Northern pike, Esox lucius Linnaeus, 1758 (Esociformes: Esocidae).

Upper Volga River, Russia.

Ventral aorta and bulbus arteriosus of heart.

24 of 121 (19.8%) northern pike sampled in 2021 were collectively infected by 28 specimens of S. plehnae.

Holotype (USNM 1688209).

urn:lsid:zoobank.org:act:2720BEA5-16A6-436D-B15D-66C1625C2B06.

The specific epithet honors Dr. Marianne Plehn (1863–1946; Bavarian Biological Experimental Institute) for her contributions to our knowledge of Sanguinicola, fish parasitology, and fish pathology as well as for her pioneering career as the first woman to be awarded (1) a doctorate by Eidgenössische Technische Hochschule in Zürich, Switzerland; (2) a Royal Professorship by King Ludwig III in Germany; and (3) doctoral status for the faculty of Veterinary Medicine at the University of Munich, Germany (Ogilvie and Harvey, 2000).

Sanguinicola plehnae differs from its congeners by having lateral tegumental spines that total 118–122, are small (3% of body width), and protrude 2–3 μm from the tegument (lacking associated conical protrusion) as well as by having a large testis (>40% of body length) (Figs. 1–3, 4A). The new species is most similar to S. hasegawai, S. rutili, and S. skrjabini by having a similar body length-to-width ratio (>4) and a testis length >40% of body length (Akhmerov, 1960; Simón-Martín et al., 1988; Shimazu, 2013). However, S. hasgawai and S. rutili have <100 lateral tegumental spines per body side (vs. >115). Sanguinicola skrjabini differs from the new species by having a larger body length-to-width ratio (>6) and >300 tegumental spines. Only 2 other species assigned to the genus, S. armata and S. volgensis, infect an esociform (both infecting northern pike, E. lucius). Given the tumultuous history of the genus, the similarities between species of Sanguinicola, and that it is unusual for a blood fluke to infect numerous fish hosts, we suspect that these records could be dubious and represent infections by several blood fluke species (Bikhovskaya-Pavlovskaya et al., 1964; Kirk and Lewis, 1994).

Sanguinicola volgensis (Rašín, 1929) Mcintosh, 1934 
(Figs. 5–13)

Body flat, ventrally concave, tapering posteriorly and anteriorly, 1,052–1,299 (1,146 ± 85, 6) long, 15–419 (358 ± 32, 7) at greatest width, 2.7–3.3× (3 ± 0.27, 6) longer than wide (Figs. 5, 12D); surface with numerous, narrow, short surface bulges, covered with heavy concentrations of shallow knoblike outgrowths (Fig. 12A, J, K), not present on the anterior body extremity, lateral conical protrusion, and cirrus (Fig. 12A, B, H, I, F, G). Tegumental body spines 21–34 (25 ± 6, 4) from anterior end (Figs. 5, 12A), 23–33 (28 ± 4, 20) long, 3 (20) wide at base, 8.3–11× longer than wide, completely encased in conical protrusion, 10–12 (20) wide (Figs. 6, 12D, H, I); tegumental spines extending to level of oötype (Figs. 5, 12D), 127–228 (153 ± 34, 7) from posterior end (Figs. 5, 12E), with 96–109 (102 ± 4, 5) per side or total of 196–211 (204 ± 7, 5). Anterior body extremity proboscislike, small, 12–18 (15 ± 3, 3) long, 13–33 (25 ± 8, 4) wide; spines absent. Ventrolateral nerve cord 999–1,074 (1,035 ± 31, 4) long, 4–12 (8 ± 3, 6) wide near midbody at widest level, 58–76 (66 ± 7, 6) from body margin. Nerve commissure perpendicular to midline of body, connecting ventrolateral nerve cords, 153–192 (167 ± 13, 6) or 15% of body length from anterior end of body, 75–110 (90 ± 12, 6) across width of worm, 7–11 (10 ± 2, 6) in breadth; secondary commissure branches 5–6 (5.6 ± 0.5, 6) in maximum width. Mouth small, 3 (3) in diameter, 3–5 (4 ± 1, 5) from terminal end of anterior body extremity (Fig. 12A–C). Pharynx present; pharyngeal canal surrounded by well-developed muscle complex of circular and radial muscle fibers (Fig. 13B). Esophagus 319–406 (341 ± 32, 6) in total length or 29–32% of body length, 11–21 (16 ± 4, 6) in maximum width (at level just anterior to nerve commissure), extending sinuously posteriad along midline, widening slightly posteriorly (Figs. 5, 8–11); anterior esophageal middle portion 59–79 (69 ± 14, 2) long, 60–75 (68 ± 11, 2) wide; posterior portion 78–109 (93 ± 16, 3) long, 54–68 (63 ± 8, 3) wide; esophageal sunken glandular cells concentrated in the middle and posterior portions. Intestine X-shaped, dendritic, with radial ceca intersecting medially, 1 specimen contained a fifth cecal lobe (Figs. 8–11); cecal intersection of anterior and posterior ceca 319–406 (341 ± 32, 6) or 29–32% of body length from anterior body end; anterior ceca 37–57 (44 ± 9, 6) long or 3–5% of body length, 14–21 (17 ± 3, 6) wide, containing granular material within lumen of some individuals (Figs. 5, 8–11); posterior ceca asymmetrical, 41–77 (59 ± 18, 6) long or 3–37% of body length, 22–46 (28 ± 12, 6) wide (Figs. 5, 8–11); postcecal space 678–817 (740 ± 50, 6) long or 64–65% of body length.

Testis 309–500 (390 ± 59, 7) long or 29–35% of body length, 158–225 (177 ± 26, 7) wide or 37–47% of body width, 2× longer than wide, postcecal, testicular lobes irregular, not paired, extending laterally, 56–106 (75 ± 16, 7) in length towards body margin (Figs. 5, 7); testicular central column large, resembling a column throughout the length of the testis, 20–36 (28 ± 6, 7) wide (Fig. 5). Posttesticular space 333–550 (413 ± 67, 7) long or 31–36% of body length. Vas deferens 56–113 (75 ± 21, 7) long, 9–16 (12 ± 3, 6) wide, emanating from posteroventral portion of testis, following midline before becoming confluent with seminal vesicle. Cirrus sac present, wall approximately 3–14 (8 ± 3.6, 7) thick, including seminal vesicle, ejaculatory duct, and cirrus; seminal vesicle 208–282 (241 ± 28, 7) long, 26–33 (29 ± 3, 7) wide, 7–10× longer than wide (Fig. 7). Male genital pore toward midline, postovarian, posterior to female genital pore, 117–185 (138 ± 25, 6) or 11–14% of body length from posterior body end (Figs. 5, 12E–G).

Ovary medial, double winged in shape, 110–160 (136 ± 18, 7) in maximum length or 10–13% of body length, 151–207 (180 ± 16, 7) wide or 44–58% of body width, 1.3–2× wider than long, immediately posttesticular; postovarian space 248–400 (291 ± 51, 7) long or 23–26% of body length (Fig. 5). Oviduct (including oviducal seminal receptacle) 211–330 (270 ± 43, 7) long; oviducal seminal receptacle 110–252 (169 ± 51, 7) long or 54–76% of oviduct length, 12–30 (19 ± 6, 7) wide. Oötype 30–38 (34 ± 3, 7) long, 22–30 (26 ± 3, 7) wide (Fig. 7). Vitellarium follicular, compacted in dense lobules, occupying space dorsal and lateral to testis and ceca, extending from nerve commissure to terminal end of posterior ceca (Fig. 5); common collecting duct 167–250 (216 ± 33, 7) long, 8–15 (11 ± 2, 7) wide. Uterus short, extending directly anteriad from oötype, 40–52 (46 ± 6, 6) long or 4% of body length, 11–28 (16 ± 8, 6) wide; containing single egg in 1 of 7 specimens; uterine egg 19 (1) long, 11 (1) wide, with thin shell. Female genital pore central, postovarian, lateral to seminal vesicle, 153–238 (177 ± 32, 6) or 15–18% of body length from posterior body end (Figs. 5, 7, 12E–G). Excretory vesicle small, 13 (1) long, 7 (1) wide, medial.

The body surface is bounded by the distal tegumental syncytial layer, which is limited by surface and basal membranes (Fig. 13F, G). Because of numerous, periodic, surface infoldings, bulges 0.7–0.8 (7.5) μm thick are present (Fig. 13F). Also, the thickness of the outer tegumental layer between the bulges is 0.35 ± 0.05 μm. A deep invagination of the basal membrane extends into the central area of each bulge (Fig. 13F, G). The tegumental cytoplasmic matrix is moderately electron dense and finely fibrous in appearance forming beneath the surface plasma membrane a dense fibrous zone, which bears regular, knoblike outgrowths (Fig. 13F, G). Numerous rounded vesicles with a slightly fibrous content are recognizable within the cytoplasm throughout the whole length of the worm’s body (Fig. 13F, G). The electron-dense spines are uniform in shape; a large proportion of spine length occurs deep beneath the level of the distal cytoplasm (Fig. 13A, D, E). In sections, diameter of the spines is 2.2–3.0 (2.6) μm; the distance between the spines varies from 4.5 to 6.2 (5.35) μm (Fig. 13A, C–E). Well-developed muscle fibers and flattened sarcoplasmic extensions are associated with each spine (Fig. 13C). The hemidesmosomes are located at the tapering ends of the muscle fibers and spine bodies (Fig. 13C).

Sabrefish, Pelecus cultratus (Linnaeus, 1758) Berg, 1949 (Cypriniformes: Leuciscidae).

Zope, Ballerus ballerus (Linnaeus, 1758) (Cypriniformes: Leuciscidae) (as Abramis ballerus) (Wierzbicka, 1977); common bream, Abramis brama (Linnaeus, 1758) (Wierzbicka, 1977) (Leuciscidae); common bleak, Alburnus alburnus (Linnaeus, 1758) (Leuciscidae) (Rašín, 1929); white bream, Blicca bjoerkna (Linnaeus, 1758) (Leuciscidae) (Wierzbicka, 1977); chub, Squalius cephalus (Linnaeus, 1758) (Leuciscidae) (as Leuciscus cephalus) (Kirk and Lewis, 1994); ide, Leuciscus idus (Linnaeus, 1758) (Leuciscidae) (Bikhovskaya-Pavlovskaya et al., 1964); common dace, Leuciscus leuciscus (Linnaeus, 1758) (Kirk and Lewis, 1994); Italian rudd, Scardinius hesperidicus Bonaparte, 1845 (Cypriniformes: Leuciscidae) (as Scardinus erythrophthalmus [Linnaeus, 1758]) (Ergens et al., 1975); northern pike, Esox lucius Linnaeus, 1758 (Esociformes: Esocidae) (Bikhovskaya-Pavlovskaya et al., 1964; Molnar, 1969; Kirk and Lewis, 1994).

Upper Volga River, Russia.

Heart lumen.

12 of 82 (14.6%) sabrefish sampled in 2021 were collectively infected by 20 specimens of S. volgensis.

Vouchers (USNM 1688210–1688216).

Sanguinicola cf. volgensis
(Figs. 14–17)

Body flat, ventrally concave, oval, 1,227 long, 239 at greatest width, 5× longer than wide, bearing longitudinal row of conical protrusions (Figs. 14; 16A, B, G, H). Tegumental surface consisting of irregular depressions and prominences (Fig. 16G, H, F); apical surface of prominences bears knoblike ornamentations (Fig. 16K). Ciliated sensory endings present, including lateral protrusions (Fig. 16H, F). Tegumental body spines 29 (10) long, 2.5 (10) wide at base, 11× longer than wide (Fig. 16A, G, H, I), completely encased in conical protrusion (Fig. 16G), 10 (10) wide, or spine emerging 2.5 from conical protrusion (Fig. 16I); tegumental spines extending to level of oötype (Fig. 16B), with 87 and 89 spines per side or total of 176. Anterior body extremity proboscislike, small, 14 long, 24 at greatest width; spines absent (Fig. 16A, B). Ventrolateral nerve cord indistinct posteriorly, 10 wide near midbody at widest level, 45 from body margin. Nerve commissure perpendicular to midline of body, connecting ventrolateral nerve cords, 187 or 15% of body length from anterior end of body, 45 or 19% of body width across width of worm, 10 in breadth. Mouth 2 in diameter, 7 from terminal end of anterior body extremity (Fig. 16C, D). Esophagus 358 in total length or 29% of body length, 10 in maximum width (at level just anterior to nerve commissure), extending sinuously posteriad along midline, widening slightly posteriorly (Fig. 14); esophageal wall 2 wide in posterior half of esophagus. Esophageal sunken glandular cells present. Intestine X-shaped, dendritic, with radial ceca intersecting medially (Fig. 14); cecal intersection of anterior and posterior ceca 358 or 29% of body length from anterior body end; anterior ceca 38 long or 3% of body length, 21 wide or 7% of body width, containing granular material within lumen (Fig. 14); posterior ceca asymmetrical, 54 long or 4% of body length, 14 wide or 6% of body width, anterior to testis (Fig. 14); postcecal space 792 long or 65% of body length.

Testis 384 long or 31% of body length, 106 wide or 44% of body width, 3.6× longer than wide, postcecal, testicular lobes irregular, not paired, extending laterally, 39 (10) in length towards body margin (Fig. 14); testicular central column large, resembling a column throughout the length of the testis, 16 (10) wide (Fig. 14). Posttesticular space 410 long or 33% of body length. Vas deferens 84 long, 8 wide, emanating from posteroventral portion of testis, following midline before becoming confluent with seminal vesicle. Cirrus sac and cirrus indistinct; seminal vesicle 180 long or 15% of body length, 23 wide or 10% of body width, 15× longer then wide, 144 or 12% of body length from posterior body end (Fig. 14). Male genital pore toward midline, postovarian, sinistral to female genital pore, 137 or 13% of body length from posterior body end (Figs. 14, 16E).

Ovary medial, double winged in shape, 108 in maximum length or 8% of body length, 116 wide or 49% of body width, 1.1× wider than long, immediately posttesticular; postovarian space 293 long or 24% of body length (Fig. 14). Oviduct 224 or 18% long. Oötype 33 long, 20 wide; 95 or 8% of body length from posterior end (Fig. 14). Vitellarium comprising diffuse follicles compacted in dense lobules, occupying space dorsal and lateral to testis and ceca, extending from anterior to nerve commissure to posterior to ovary (Fig. 14). Uterus short, extending directly anteriad from oötype, 34 long or 3% of body length, 3 wide. Female genital pore mediodextral, postovarian, lateral to seminal vesicle, 144 or 11% of body length from posterior body end (Fig. 16E, J). Excretory vesicle indistinct.

Body flat, ventrally concave, ovoid, 1,324 long, 205 at greatest width, 6× longer than wide (Fig. 15). Tegumental body spines 27 (10) long, 3 (10) wide at base, completely encased in tegument (Fig. 15), tegumental spines extending to level of oötype, with 92 and 94 spines per side or total of 186. Esophagus 406 in total length or 31% of body length, 22 in maximum width, extending sinuously posteriad along midline, widening slightly posteriorly. Esophageal sunken glandular cells concentrated immediately anterior to cecal bifurcation, 185 in total length or 46% of esophagus length, 47 in maximum width (Fig. 15). Intestine X-shaped, with paired anterior and posterior ceca intersecting medially; cecal intersection of anterior and posterior ceca 406 or 31% of body length from anterior body end; anterior ceca 42 long or 3% of body length, 22 wide or 11% of body width, containing granular material within lumen (Fig. 15); posterior ceca asymmetrical, 75 long or 6% of body length, 37 wide or 18% of body width, anterior to testis; postcecal space 832 long or 63% of body length. Testis 316 long or 24% of body length, 108 wide or 53% of body width, 2.9× longer than wide, postcecal, testicular lobes irregular, not paired, extending laterally, 53 (10) in length towards body margin (Fig. 15). Posttesticular space 358 long or 27% of body length. Terminal genitalia and excretory vesicle not observed.

TEM shows that distal tegumental cytoplasmic layer of the body tegument greatly varies in thickness 0.1–2.0 (1.05) μm, depending on the degree of surface irregularity, which is penetrated by various kinds of numerous, large, and deep surface invaginations, forming numerous prominences (Fig. 17B, G, H). The apical ends of these prominences are electron dense at about 0.25 ± 0.05 μm in their length, forming knoblike ornamentation shown via SEM (Figs. 16K, 17G, H). The tegumental cytoplasmic matrix is moderately electron dense and finely fibrous in appearance, with a dense fibrous zone beneath the surface plasma membrane, and contains a high concentration of small, electron-lucent vesicles and rare single electron-dense, oval granules 0.3 ± 0.01 × 0.2 ± 0.01 μm (Fig. 17G–I). The vesicles are elongated about 0.15 ± 0.01 × 0.06 ± 0.01 μm and can be recognized by their electron-dense walls (Fig. 17I). The basal plasma membrane of the syncytial layer extends into long invaginations, penetrating the central area of the prominences (Fig. 17G, H). The conical protrusions are scattered along the lateral body margins (Fig. 17A, C, D). Each protrusion possesses 1 spine, much of the length of which occurs deep beneath the level of the distal cytoplasm (Fig. 17C, D). The diameter of the spines varies between 1.7–2.2 (1.95) μm. The distance between spines is 6.5–8.0 (7.25) μm. Spines are uniform in the shape and have an electron-dense body surrounded by muscle fibers and flattened sarcoplasmic extensions (Fig. 17B–F). Hemidesmosomes are located between the muscle fibers and the spine body (Fig. 17F).

Ide, Leuciscus idus (Linnaeus, 1758) Berg, 1949 (Cypriniformes: Leuciscidae).

Upper Volga Region, Russia.

Heart lumen.

22 of 67 (32.8%) ide sampled in 2021 were infected by a collective total of 47 specimens of S. cf. volgensis.

Vouchers (USNM 1688217, 1688218).

We identified the blood fluke specimens infecting ide as Sanguinicola cf. volgensis, because our specimens were morphologically indistinguishable from the published description and the newly collected material (see previous discussion), although they have a larger body length:width ratio (5–6 vs. 2–3) and <90 lateral tegumental spines (vs. >95). The juvenile specimen had large lateral tegumental spines but lacked the conical protrusion associated with the spine (Fig. 15), which is noteworthy regarding their taxonomic identity.

Sanguinicola volgensis differs from its congeners by having posteriorly directed lateral tegumental spines encased in a tegumental conical protrusion (Figs. 5, 6, 12H–I, 13D). Rašín (1929) described Sanguinicola volgensis (as Janickia Rašín, 1929) based on the length of the metraterm (longer than oötype vs. shorter than oötype) and egg shape (oval vs. triangular). McIntosh synonymized Janickia with Sanguinicola, stating “Janickia is regarded by the writer as a synonym of Sanguinicola, since, according to Rašín (1929), it does not differ from the genus Sanguinicola except in shape and size of the egg, oötype, and metraterm; the species Janickia volgensis Rašín, 1929, therefore, becomes Sanguinicola volgensis (Rašín, 1929) n. comb” (McIntosh, 1934:465). McIntosh did not elaborate further. Because several species assigned to the Sanguinicola sensu stricto are described as having an ovoid egg, we accept the synonymy, that is, Janickia herein remains a junior subjective synonym of Sanguinicola. 4 species assigned to Sanguinicola sensu stricto reportedly have ovoid eggs (S. lophophora, S. rhodei, S. hasegawai, S. magnus), 4 reportedly have triangular eggs (S. armata, S. intermedia, S. lungensis, S. rutili), and 1 has “approximately triangular” eggs (S. rhodei) (Wang, 1983:34). No description of an egg was given for S. skrjabini (Akhmerov, 1960). Further, we did not observe an egg in the uterus for S. plehnae. In 1 of 7 of our whole-mounted specimens of S. volgensis, we observed a single ovoid egg within the lumen of the distal uterus. Further collections are required to determine the egg shape in this species.

Pseudosanguinicola Warren and Bullard n. gen.
(Figs. 18–20)

Body of adult <7× longer than wide, dorsoventrally flat, lacking posterolateral protuberance, tapering equally anteriorly and posteriorly, ventrally concave, spined; tegumental spines delicate, straight and not distally recurved, arranging in densely compacted transverse rows along lateral body margin, appearing irregular or discordant. Rose-thorn–shaped spines absent. Ventrolateral nerve cords and dorsolateral nerve cords present; ventrolateral nerve cord appearing slightly subterminal, with commissure anteriorly. Anterior sucker diminutive, appearing concave, accommodating mouth; mouth medioventral, subterminal, with associated toothlike mouth apparatus (Figs. 4I, 12B). Pharynx indistinct. Esophagus medial, straight, not looping, extending posteriad less than one-fourth body length, with anterior and posterior esophageal swellings, with esophageal gland enveloping posterior portion of esophagus, connecting with ceca, anteromedially. Intestine thin walled, medial, comprising 4 radial ceca that collectively appear generally as an X-shaped structure. Testis diffuse, an array of lateral lobes, with breadth equal or slightly greater than that of intestine, giving the appearance of multiple testes in 2 tandem rows flanking midline from level of ceca to middle third of body. Vasa efferentia prominent, appearing to occupy one-third of the testicular width, with secondary ducts extending from lateral margins of testicular lobes and coalescing ventrally along midline, narrowing medially before connecting with proximal portion of seminal vesicle. Cirrus sac surrounding seminal vesicle present, but inconspicuous in some whole mounts. Male genital pore dextral, slightly lateral to midline. Ovary single, medial, with superficial lobed margins, with lateral portions extending anteriad and lateral to posterior portion of testicular field, appearing butterfly- wing shaped to varying degrees, as wide or wider than testicular field, occupying posterior one-third of body. Vitellarium follicular, at least occupying space from about level of anterior nerve commissure to terminal end of ovary. Oviduct a narrow duct extending directly posteriad from posteromedial surface of ovary, connecting with distal portion of vitelline reservoir to or near level of male genital pore; oviducal seminal receptacle present or absent. Ovovitelline duct connecting with oötype posteriorly. Oötype large, oblong, lateral and posterior to level of male genital pore, posterior to genitalia. Laurer’s canal absent. Uterus short, straight; uterine seminal receptacle lacking. Female genital pore anteromedial to male genital pore. Excretory vesicle not observed.

Body <7× longer than wide; tegumental spines delicate, straight and not distally recurved, arranging in densely compacted transverse rows along lateral body margin, appearing irregular or discordant. Intestine X-shaped, with 4 radial ceca, terminating in anterior half of the body. Testis single, an array of lateral lobes, with breadth equal or slightly greater than that of intestine, giving the appearance of multiple testes in 2 tandem rows flanking midline from level of ceca to middle one-third of body. Seminal vesicle medial, large, one-fourth to one-third of body length. Male genital pore lateral to female genital pore, terminating along midline. Ovary butterfly-wing shaped, postcecal, posttesticular. Oötype large, posterior to genitalia. Uterus short, straight, equal in length of oötype.

Pseudosanguinicola occidentalis (Van Cleave and Mueller, 1932) Warren and Bullard n. comb.

urn:lsid:zoobank.org:act:D09CC45D-3EB2-40E0-AECD-76D745B80578.

The Greek “pseudo” refers to the previous assignment of this species to Sanguinicola.

Pseudosanguinicola Warren and Bullard n. gen. resembles Sanguinicola and Nomasanguinicola by having an anterior esophageal swelling, an intestine terminating in the anterior half of the body, a vitelline duct dorsal to the testis, an ovary that is butterfly-wing shaped, and male and female genital pores that open near the midline. It differs from Nomasanguinicola by lacking an anterior sucker with 2 columns of denticles flanking the mouth (Truong and Bullard, 2013). Further, it differs from Sanguinicola sensu stricto by having lateral tegumental spines that are delicate, straight, and not distally recurved, distributed in densely compacted transverse rows along the lateral body margin, appearing grasslike and discordant (Figs. 18, 19). Pseudosanguinicola is most similar to species we regard as incertae sedis (S. alseae, S. davisi, S. fontinalis, S. idahoensis, S. klamathensis, S. maritimus, and S. ugui) (Table II) by having tegumental spines in transverse rows rather than a single column. Of those 7 species, S. idahoensis is most similar by having “numerous spines along the lateral tegument” (Schell, 1974:562). The illustration of S. idahoensis does not help determine homology of the spines. Further, S. alseae, S. davisi, S. idahoensis, and S. klamathensis have a prominent proboscislike anterior sucker with circumoral spines (Wales, 1958; Holmes, 1971; Schell, 1974). Considering these differences (transverse rows and a prominent proboscislike anterior sucker) and that they infect species from North America, the blood flukes infecting salmoniforms may represent a new genus.

Pseudosanguinicola occidentalis (Van Cleave and Mueller, 1932 ) Warren and Bullard n. comb.
(Figs. 18–20)

Body flat, ventrally concave, ovoid, 1,145–1,527 (1,324 ± 157, 5) long, 162–271 (230 ± 41, 5) at greatest width, 5–7.1× (5.7 ± 0.92, 5) longer than wide (Fig. 18); body constricted posteriorly producing taillike appendage, 176–223 (205 ± 20, 4) from terminal end (Fig. 18). Tegumental body spines 2–3.5 (2.8 ± 1.1, 20) long, 1–1.5 (1.3 ± 0.4, 20) wide at base, densely packed, not extending beyond tegument, tegumental spines extending to level of female genital pore in posterior half (Fig. 19). Anterior sucker, small, 11–17 (14 ± 4, 2) long, 19–21 (20 ± 1, 2) at greatest width; spines absent. Ventrolateral nerve cord indistinct. Nerve commissure perpendicular to midline of body, connecting ventrolateral nerve-cords, 129–149 (139 ± 14, 2) or 11% of body length from anterior body end, 54–63 (59 ± 6.4, 2) across width of worm, 9–11 (10 ± 2, 2) in breadth; secondary commissure branches indistinct. Mouth 2.5 in diameter, 2 from anterior of body. Esophagus 291–359 (325 ± 34, 3) in total length or 24% of body length, 16–22 (19 ± 3, 3) in maximum width (at level just anterior to nerve commissure), extending sinuously posteriad along midline, widening in anterior portion 34 long and 13 wide; esophageal wall thickening from 3 to 7 (5 ± 1, 4) in maximum width. Esophageal gland indistinct. Intestine thin walled, medial comprising 4 radial ceca that collectively appear generally X-shaped (Fig. 18); anterior ceca 25–32 (29 ± 5, 2) long or 2% of body length, 15 wide, containing granular material within lumen of some individuals; posterior ceca asymmetrical, 34–40 (37 ± 5, 2) long or 3% of body length, 17 wide, anterior to testis (Fig. 18); postcecal space 879–1034 (957 ± 110, 2) long or 61–70% of body length.

Testis 389–409 (392 ± 12, 4) long or 28–34% of body length, 39–101 (31 ± 3, 4) wide or 24–30% of body width, 5–10× longer than wide, postcecal, testicular lobes irregular, not paired, extending laterally, 57–76 (64 ± 9, 4) in length towards body margin (Figs. 18, 20); testicular middle column 12–59 (33 ± 17, 5) wide. Posttesticular space 367–660 (510 ± 147, 3) long or 32–46% of body length. Vas deferens 101–150 (119 ± 27, 3) long, 5–12 (7 ± 4, 3) wide, emanating from posteroventral portion of testis, following midline before becoming confluent with seminal vesicle. Cirrus sac present, including seminal vesicle and cirrus; seminal vesicle 239–480 (340 ± 125, 3) long, 15–38 (30 ± 11, 4) wide, 21–33% (3) of body length (Fig. 20). Cirrus 13–37 (25 ± 17, 2) long or 5–12% of seminal vesicle length, 6–8 (7 ± 1.4, 2) wide. Male genital pore toward midline, postovarian, sinistral to female genital pore, 114–187 (143 ± 39, 3) or 9–12% of body length from posterior body end (Fig. 20).

Ovary medial, double winged in shape, 120–313 (192 ± 106, 3) long or 10–21% of body length, 66–123 (99 ± 29, 3) wide or 41–45% of body width, immediately posttesticular; postovarian space 232–390 (326 ± 83, 3) long or 20–29% of body length (Figs. 18, 20). Oviduct (including oviducal seminal receptacle) 282–433 (365 ± 77, 3) long; oviducal seminal receptacle 85 long or 30% of oviduct length, 13 wide. Oötype 28–46 (39 ± 9, 4) long, 16–47 (33 ± 14, 4) wide, 65–120 (84 ± 31, 4) long from posterior terminal end (Figs. 18, 20). Vitellarium comprising follicles compacted in dense lobules, occupying space dorsal and lateral to testis and ceca, extending from anterior to nerve commissure to terminal end of ovary (Fig. 18); common collecting duct 375–404 (390 ± 21, 2) long, 11–19 (15 ± 3.3, 2) wide. Uterus short, extending directly anteriad from oötype, 23–50 (35 ± 11, 4) long or 2–3% of body length, 17–22 (20 ± 3, 4) wide; uterine eggs not observed. Female genital pore medial, postovarian, lateral to male genital pore, 133–213 (167 ± 34, 4) or 12–14% of body length from posterior body end (Figs. 18, 20). Excretory vesicle not observed.

Walleye, Sander vitreus (Mitchill, 1818) Bailey et al., 2004 (Perciformes: Percidae).

Yellow perch, Perca flavescens (Mitchill 1814) Collette and Bănărescu, 1977 (Perciformes: Percidae).

Oneida Lake, New York.

Lewis Point, Oneida Lake, Lenox, New York (Madison County): (43°10′24″N, 75°46′35″W); Wisconsin.

Heart lumen.

2 of 2 (100%) walleye sampled on 7 July 2020 were infected by 1 specimen each of P. occidentalis; 6 of 16 (38%) walleye sampled on 20 August 2020 collectively were infected by 8 specimens of P. occidentalis.

Vouchers (USNM 1688219–1688223).

Pseudosanguinicola occidentalis resembles the accepted Sanguinicola spp. (Table I) by having an intestine that is X-shaped, with 4 radial ceca terminating in the anterior half of the body, a single testis with lobes extending laterally, a double winged or butterfly-wing shaped ovary, male and female genital pores terminating along the midline, and a short uterus. It differs from Sanguinicola spp. most notably by the arrangement of the lateral tegumental spines, which are densely compacted transverse lateral rows vs. single column of large spines (Figs. 2, 6, 19). Pseudosanguinicola occidentalis also resembles S. rhodei by having a lappetlike posterior end that begins at level of the genital pores and oötype (Fig. 18). Before collecting new material, we (M.B.W., S.A.B.) incorrectly predicted that this was fixation artifact. Van Cleave and Mueller described 2 vitelline ducts connecting to the oötype (Van Cleave and Mueller, 1932). Our newly collected specimens have a single vitelline duct (Fig. 20), which is large and obvious. Depending on the condition of the Van Cleave and Mueller specimens, these delicate ducts could have been difficult for them to discern. They also described minute cuticular spines covering most of the body, but this is not the case in our material and likely represents sensory cilia (Ejsmont, 1926; Van Cleave and Mueller, 1932).

The amplified 28S and internal transcribed spacer 2 region (ITS2) fragments representing S. volgensis, S. cf. volgensis, and S. plehnae are 1,584, 1,585, and 1,574 nucleotides and 451, 461, and 452 nucleotides, respectively. The amplified 28S fragment representing P. occidentalis is 1,589 nucleotides. Sequences representing S. volgensis and S. cf. volgensis were recovered sister to one another and only differed by a single base pair in the 28S (Fig. 21) and 2 base pair differences in the ITS2 (2 bp; 99.6% similar). The 28S sequence representing S. plehnae differed from S. volgensis and S. cf. volgensis by 82 and 83 nucleotides (28S) and by 37 and 39 nucleotides (ITS2), respectively. The species was recovered sister to the clade including S. volgensis and S. cf. volgensis. The 28S sequences (S. volgensis, S. cf. volgensis, S. plehnae) grouped sister to the cercarial sequence for Sanguinicola cf. inermis (AY222180) and yielded a percent similarity of 81% (218 bp) (Olson et al., 2003) (Fig. 21). It is noteworthy that this 28S sequence (AY222180) is from a cercaria infecting a gastropod from a lake in Poland that has never been confirmed with the adult specimen (Olson et al., 2003). That said, S. volgensis (like the type species, S. armata) differs from S. inermis (see Remarks) by having large spikelike tegumental spines in a single column (Fig. 6) (Plehn, 1905; Ejsmont, 1926). The large % bp difference between S. volgensis and S. cf. inermis (218 bp) is similar to intergeneric sequence variability rather than interspecific variation. For example, sequences representing species of Psettarium Goto and Ozaki, 1930 and Cardallagium Yong, Cutmore, Jones, Gauthier, and Cribb, 2018 (formally assigned to Psettarium) differ by 217 bp (Warren et al., 2017a; Yong et al., 2018).

Pseudosanguinicola occidentalis was recovered sister to all species of Sanguinicola and differed from S. volgensis, S. cf. volgensis, S. plehnae, and S. cf. inermis by 158, 157, 183, and 236 bp (28S), respectively (Fig. 21). Further, P. occidentalis and Sanguinicola spp. were monophyletic and sister to the remaining actinopterygian blood flukes assigned to Elopicola Bullard, 2014; Aporocotyle Odhner, 1900; Plethorchis Martin, 1975; Neoparacardicola Yamaguti, 1970; Skoulekia Alama-Bermejo, Montero, Raga, and Holzer, 2011; and Psettarium Goto and Ozaki, 1930.

The chondrichthyan blood flukes (Chimaerohemecus trondheimensis Van der Land, 1967, Gymnurahemecus bulbosus Warren, Ruiz, Whelan, Kritsky, and Bullard, 2019; Ogawaia glaucostegi Cutmore, Cribb, and Yong, 2018; Electrovermis zappum Warren and Bullard, 2019) and acipenseriform blood flukes (Acipensericola spp.) were recovered sister to all other actinopterygian blood flukes (Fig. 21; Table III). Acipensericola petersoni Bullard, Snyder, Jensen, and Overstreet, 2008 and Acipensericola glacialis Warren and Bullard, 2017 were recovered sister to the chondrichthyan blood flukes with low nodal support (0.51). Acipensericola petersoni and A. glacialis differ from P. occidentalis and species of Sanguinicola by 310 and 363 bp (79% similarity), respectively. Given the low nodal support for the clade representing the chondrichthyan blood flukes and actinopterygian blood flukes, we expect some change to the tree topology as more taxa are added and analyzed.

We thank Thomas Brooking (Cornell Biological Field Station) for helping collect the infected walleye. We also thank Anna Phillips, Chad Walter, Kathryn Ahlfeld, and William Moser (all Department of Invertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, DC) for curating our museum specimens. This study was supported by Southeastern Cooperative Fish Parasite and Disease Project (Auburn University), the U.S. Fish and Wildlife Service (Department of Interior), National Sea Grant (National Oceanic and Atmospheric Administration), United States Department of Agriculture (National Institute of Food and Agriculture), Federal Aid in Sport Fish Restoration (Alabama Department of Conservation and Natural Resources, Inland and Marine Resources Divisions), and the Alabama Agricultural Experiment Station (Auburn University, College of Agriculture) as well as the Russian Foundation for Basic Research.