MOLECULAR PHYLOGENETIC ANALYSIS OF GYRINICOLA BATRACHIENSIS (NEMATODA: OXYUROIDEA) LENDS SUPPORT TO THE MONOPHYLY OF THE GENUS AND THE RESURRECTION OF GYRINICOLINAE.

Gyrinicola Yamaguti, 1938, includes 6 species of oxyurid found within the intestinal tract of numerous, larval, anuran species in Europe, Asia, South America, and North America. The systematic placement and hierarchical treatment of the genus has shifted at least 5 times since its discovery; the group was first considered as its own family (Gyrinicolidae), then treated as a subfamily (Gyrinicolinae) of Cosmocercidae, then as a member of the Pharyngodonidae, followed by movement back to the Cosmocercidae, and finally a recent proposal suggested the resurrection of the Gyrinicolidae. Species in the genus vary widely in the morphology of the uterine tract, a characteristic often used to indicate membership in the genus, as it is tied to the reproductive mode. However, until recently very few genetic data were available to aid in the placement of this unique group of worms, and before this study to the best of our knowledge none existed for the North American species. To examine the monophyly and placement of the Gyrinicola we sampled populations of Gyrinicola batrachiensis across North America and screened them for genetic diversity using nuclear markers 18S and 28S. Phylogenies suggest at least 3 clades exist among the nematodes from North America and that these clades, alongside Gyrinicola japonica, form a well-supported group within Oxyuroidea. Further representation of Pharyngodonidae from other vertebrate classes may help clarify the relationship of this historical grouping to other members of the Oxyuroidea.

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

Sanguinicola Plehn, 1905 comprises 26 species that collectively infect fishes from 8 orders (Cypriniformes, Characiformes, Siluriformes, Esociformes, Salmoniformes, Labriformes, Centrarchiformes, and Perciformes). Its revision is warranted because several species assigned to the genus could represent new genera, nucleotide sequences are wanting, many species have incomplete descriptions, and types for most species are missing or of poor quality. Herein, we emend Sanguinicola based on morphology and the first nucleotide-based phylogenetic analysis that includes multiple sequences from morphologically identified adult specimens. We describe Sanguinicola plehnae Warren and Bullard n. sp. from the heart of northern pike, Esox lucius Linnaeus, 1758 from Russia; provide supplemental observations of Sanguinicola volgensis (Rasín, 1929) McIntosh, 1934 from the heart of sabrefish (type species), Pelecus cultratus (Linnaeus, 1758) Berg, 1949 from Russia; describe Sanguinicola cf. volgensis from the heart of ide, Leuciscus idus (Linnaeus, 1758) Berg, 1949 from Russia; and describe Pseudosanguinicola occidentalis (Van Cleave and Mueller, 1932) Warren and Bullard n. gen., n. comb. from the heart of walleye, Sander vitreus (Mitchill, 1818) Bailey, Latta, and Smith, 2004 from eastern North America. 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). Sanguinicola volgensis differs from its congeners by having posteriorly directed lateral tegumental spines encased in a tegumental conical protrusion as well as by having an ovoid egg. Specimens of S. cf. volgensis differ from those of S. volgensis by having a body that is 5-6× longer than wide (vs. 2-3× in S. volgensis) and <90 lateral tegumental spines (vs. >95). Pseudosanguinicola Warren and Bullard n. gen. differs from Sanguinicola by having densely transverse rows of lateral tegumental spines (vs. a single column of large spines). The phylogenetic analysis utilizing the large subunit ribosomal DNA (28S) failed to reject monophyly of Sanguinicola.

RESURRECTION OF PLESIOCREADIUM WINFIELD, 1929 (DIGENEA: MACRODEROIDIDAE) WITH PHYLOGENETIC ANALYSES AND SUPPLEMENTAL OBSERVATIONS OF ITS TYPE SPECIES FROM RIVERS IN ARKANSAS, MISSISSIPPI, NEW YORK, AND TENNESSEE.

We herein resurrect and emend PlesiocreadiumWinfield, 1929 (Digenea: Macroderoididae) and provide a supplemental description of its type species, Plesiocreadium typicumWinfield, 1929, based on adult specimens collected from the intestine of bowfins, Amia calva Linnaeus, 1766 (Amiiformes: Amiidae), captured in the L'Anguille River (Mississippi River Basin, Arkansas), Big Lake (Pascagoula River Basin, Mississippi), Chittenango Creek (Oneida Lake, New York), and Reelfoot Lake (Tennessee River Basin, Tennessee). Plesiocreadium spp. (Pl. typicum and Plesiocreadium flavum [Van Cleave and Mueller, 1932] n. comb.) differ from other macroderoidids by having a dorsoventrally flat forebody, ceca that extend posteriad beyond the testes and that do not form a cyclocoel, testes that are greater than one-half of maximum body width, a cirrus sac that is dorsal to the ventral sucker and arches dextrad or sinistrad, a uterine seminal receptacle, asymmetrical vitelline fields that remain separated anteriorly and posteriorly and that extend anteriad to the level of the ventral sucker, and an I-shaped excretory vesicle. Bayesian phylogenetic analyses (ITS2 and 28S) recovered monophyletic Plesiocreadium sensu stricto (as defined herein) sister to Macroderoides trilobatusTaylor, 1978 and that clade sister to the remaining macroderoidids, with sequences ascribed to species of Macroderoides Pearse, 1924 recovered as paraphyletic. We regard Macroderoides parvus (Hunter, 1932) Van Cleave and Mueller, 1934, M. trilobatus, and RauschiellaBabero, 1951 as incertae sedis. Arkansas, New York, and Tennessee comprise new locality records for Pl. typicum.

Plagioporus wataugaensis n. sp. (Digenea: Opecoelidae) infecting intestine of northern hogsucker, Hypentelium nigricans, and white sucker, Catostomus commersonii, (Cypriniformes: Catostomidae) from the eastern USA, including an emended diagnosis, key to Nearctic congeners, and phylogenetic analysis.

We describe a new species of Plagioporus Stafford, 1904 infecting the intestine of two catostomids in the eastern USA. We emend Plagioporus to account for Nearctic congeners having ceca terminating at the level of the testes (previously diagnosed as having ceca terminating in the post-testicular space only) and testes in the posterior body extremity (a feature not previously considered as having generic importance). Of the accepted Nearctic species, Plagioporus wataugaensis n. sp. resembles Plagioporus serotinus Stafford, 1904, Plagioporus hypentelii Hendrix, 1973, and Plagioporus hageli Fayton and Andres, 2016 but differs from them by the distribution of the vitellarium and proportional length and relative extent of the excretory vesicle. Plagioporus wataugaensis has vitelline fields that are discontinuous at the level of the ventral sucker (vs. continuous in P. serotinus and P. hypentelii) and follicles that surround the ceca (vs. wholly ventral to the ceca in P. hageli) and that span the midline dorsal to the testes (vs. slightly overlapping the lateral margins of the testes). The excretory vesicle of P. wataugaensis is wholly post-testicular and short (6-9% of the body length) (vs. reaching the level of the posterior testis, 14-24% of the body length). Phylogenetic analyses of the 28S, ITS1, 5.8S, and ITS2 rDNA recovered P. wataugaensis sister to Plagioporus sinitsini Mueller, 1934. A key to the Nearctic Plagioporus spp. is provided. We regard Plagioporus shawi (McIntosh, 1939) Margolis, 1970, Plagioporus serratus Miller, 1940, and Plagioporus loboides (Curran, Overstreet, and Tkach, 2007) Fayton and Andres, 2016 as incertae sedis.

TWO NEW SPECIES OF STILLABOTHRIUM (CESTODA: RHINEBOTHRIIDEA) FROM STINGRAYS FROM NORTHERN AUSTRALIA AND ONE NEW COMBINATION.

A study of cestode specimens that were collected during survey work on elasmobranchs collected from Taiwan and Northern Territory, Australia, revealed the presence of 1 new combination into the genus Stillabothrium (Rhinebothriidea: Escherbothriidae) and 2 new species of the genus. Phyllobothrium biacetabulatum, collected from Rhinobatos schlegelii, is transferred to Stillabothrium and its description is emended, as is the diagnosis for the genus Stillabothrium and the family Escherbothriidae. Stillabothrium biacetabulatum n. comb. differs from existing species of the genus in that the face of its bothridia is laced with a network of longitudinal and horizontal muscle fibers that do not contribute to the formation of septa. Stillabothrium lunae n. sp. is described from Himantura leoparda and differs from existing species of the genus in that its bothridium possesses an anterior field of 7-8 loculi that are wider than long. Stillabothrium mariae n. sp. is described from Maculabatis astra. This species differs from all species of Stillabothrium except Stillabothrium campbelli in possessing 10-12 horizontally oriented bothridial loculi. Stillabothrium mariae n. sp. differs from S. campbelli in having longer bothridia and from all other species of Stillabothrium in that it lacks, rather than possesses, conspicuous septa and loculi that are longer than wide in the posterior region of its bothridia. Bayesian and parsimony-bootstrap analysis of 28S rDNA revealed S. biacetabulatum n. comb., S. lunae n. sp., and S. mariae n. sp. to be part of Clade 1 of Stillabothrium, with S. biacetabulatum n. comb. being the sister species to S. mariae n. sp. Stillabothrium lunae n. sp. was found to be the sister species to Stillabothrium borneoense.

High Prevalence of the Copepod Salmincola californiensis in Steelhead Trout in Lake Ontario Following its Recent Invasion.

Salmincola californiensis (Dana, 1853) (Subclass Copepoda: Family Lernaeopodidae) is known to parasitize salmonids of the genus Oncorhynchus including Oncorhynchus mykiss (rainbow trout), Oncorhynchus tshawytscha (chinook salmon), and Oncorhynchus kisutch (coho salmon). These 3 salmonids have been introduced to the Great Lakes intermittently since the mid-1800s. As we demonstrate here, the introduction of these salmonids to the Great Lakes was followed, at some point, by the introduction of their parasitic gill copepod, S. californiensis. Given anecdotal accounts of S. californiensis in introduced salmonids in Lake Ontario since 2012, we chose to conduct a survey to formally document the occurrence of this introduced species. Our survey took place during spring, summer, and fall of 2018 and during spring of 2019 at the south-eastern side of Lake Ontario. Prevalence of S. californiensis was 69, with a mean intensity of 2.7 in 61 rainbow trout examined in 2018. In 2019, prevalence of S. californiensis was 71, with a mean intensity of 3.6 in 59 rainbow trout examined. The prevalence of S. californiensis was 39, with a mean intensity of 1.6 in 223 chinook salmon examined in 2018. No specimens of S. californiensis were found in the 100 coho salmon examined in 2018. The prevalence of S. californiensis in rainbow trout is of great concern considering that it is double that found in rainbow trout in the native range (69 [in 2018] and 71 [in 2019] vs. 35). This is the first formal documentation of the invasion of S. californiensis in Lake Ontario. Future fisheries management decisions in Lake Ontario and its tributaries should take into account these data.

Two new species of Stillabothrium (Cestoda: Rhinebothriidea) from stingrays of the genus Fontitrygon from Senegal.

Morphological and molecular analyses of cestode specimens collected during survey work of batoid elasmobranchs and their parasites in Senegal revealed two new species of the rhinebothriidean cestode genus Stillabothrium Healy et Reyda 2016. Stillabothrium allisonae Dedrick et Reyda sp. n. and Stillabothrium charlotteae Iwanyckyj, Dedrick et Reyda sp. n. are both described from Fontitrygon margaritella (Compagno et Roberts) and Fontitrygon margarita (Günther). Both new cestode species overlap in geographic distribution, host use and proglottid morphology, but are distinguished from each other, and from the other seven described species of Stillabothrium, on the basis of their pattern of bothridial loculi. Phylogenetic analyses based on sequence data for 1,084 bp from the D1-D3 region of 28S rDNA that included multiple specimens of both new species and eight other species of Stillabothrium corroborated the morphologically-determined species boundaries. The phylogenetic analyses indicate that S. allisonae sp. n. and S. charlotteae sp. n. are sister species, a noteworthy pattern given that the two species of the stingray genus Fontitrygon they both parasitise, F. margaritella and F. margarita, are also sister species. Although species of Stillabothrium vary widely in their patterns of facial loculi, the variation does not appear to correlate with phylogeny. Most species of Stillabothrium parasitise myliobatiform elasmobranch genera of the Dasyatidae Jordan. This study brings the number of described species of Stillabothrium to nine, three of which occur in the eastern Atlantic, two of which occur off the northern coast of Australia, and four of which are from coastal Borneo.

INTRODUCTION OF THE 2018 RECIPIENT OF THE AMERICAN SOCIETY OF PARASITOLOGISTS' CLARK P. READ MENTOR AWARD, DR. JANINE N. CAIRA.

There is no abstract.

A new genus of rhinebothriidean cestodes from batoid elasmobranchs, with the description of five new species and two new combinations.

Survey work of batoid elasmobranchs in the eastern Atlantic and Indo-Pacific revealed multiple species of a new genus of cestode. Stillabothrium Healy et Reyda gen. n. (Rhinebothriidea: Escherbothriidae) is unique in its possession of an even number of non-medial longitudinal septa in the posterior portion of the bothridia, resulting in a series of loculi that are longer than wide (i.e. vertically oriented) and are arranged in columns. Five new species of Stillabothrium are described, S. ashleyae Willsey et Reyda sp. n., S. davidcynthiaorum Daigler et Reyda sp. n., S. campbelli Delgado, Dedrick et Reyda sp. n., S. hyphantoseptum Herzog, Bergman et Reyda sp. n., S. jeanfortiae Forti, Aprill et Reyda sp. n., and two species are formally transferred to the genus, S. amuletum (Butler, 1987) comb. n., and S. cadenati (Euzet, 1954) comb. n., the latter of which is redescribed. The species differ in the configuration of the other bothridial septa and in proglottid anatomy. Species of Stillabothrium were found parasitising a total of 17 species of batoid elasmobranchs of the genera Dasyatis Rafinesque, Glaucostegus Bonaparte, Himantura Müller et Henle, Pastinachus Rüppell, Rhinobatos Linck and Zanobatus Garman, including several host species that are likely new to science. A phylogenetic hypothesis based on Bayesian analysis of 1 084 aligned positions of the D1-D3 region of 28S rDNA for 27 specimens representing 10 species of Stillabothrium and two outgroup species supported the monophyly of Stillabothrium. These results also supported morphologically determined species boundaries in all cases in which more than one specimen of a putative species was included in the analysis. Host specificity appears to vary across species of Stillabothrium, with the number of host species parasitised by each species of Stillabothrium ranging from one to four. The geographic distribution of species of Stillabothrium spans the eastern Hemisphere, including the eastern Atlantic (coastal Senegal) and several locations in the Indo-Pacific (coastal Vietnam, Borneo and Australia). In addition, Phyllobothrium biacetabulatum Yamaguti, 1960 is formally transferred into family Escherbothriidae, although its generic placement remains uncertain (species incertae sedis).

Two new and one redescribed species of Acanthobothrium (Cestoda: Onchoproteocephalidea: Onchobothriidae) from Dasyatis akajei (Myliobatiformes: Dasyatidae) in the China Sea.

Acanthobothrium ningdense n. sp. and Acanthobothrium guanghaiense n. sp. are described from the spiral intestine of the whip stingray, Dasyatis akajei (Müller & Henle). Acanthobothrium ningdense n. sp. is reported based on 38 cestode specimens collected at five locations along the Chinese coast, i.e. Taizhou, Zhejiang Province, Ningde and Xiamen, Fujian Province, Taishan, Guangdong Province and Sanya, Hainan Province between 2012 and 2015. Acanthobothrium ningdense n. sp. belongs to the "species category 4" characterised by Ghoshroy & Caira. Among category 4 Acanthobothrium species, A. ningdense n. sp. most closely resembles A. micracantha Yamaguti, 1952 and A. latum Yamaguti, 1952, both from the same host species. Acanthobothrium ningdense n. sp. differs from A. micracantha by lacking a long robust hook handle that connects the bases of medial and lateral hooks, and from A. latum by having much longer axial prongs than abaxial prongs. Acanthobothrium guanghaiense n. sp., only found in Taishan, Guangdong Province in 2014, is a category 2 Acanthobothrium species. Among category 2, A. guanghaiense n. sp. most closely resembles A. semnovesiculum Verma, 1928, but can be differentiated from it by the arrangement of testes (in two staggered columns rather than in two tandem columns), and the shape of abaxial prong (nearly straight instead of with a conspicuous curve in the proximal portion). Acanthobothrium macrocephalum Wang & Yang, 2001 is redescribed based on new specimens collected from D. akajei in Guanghai and Sanya. With this study, the total number of Acanthobothrium species reported from D. akajei is brought to nine. It is possible that some of the species of Acanthobothrium previously reported from D. akajei not encountered in this study may have geographically restricted distributions, as was observed here for A. guanghaiense n. sp..

Histopathology of Catostomus commersoni (White Sucker) Infected with the Acanthocephalan Pomphorhynchus bulbocolli.

This study was undertaken to assess the damage caused by Pomphorhynchus bulbocolli to Catostomus commersoni (white sucker). Three specimens of C. commersoni were collected during early September 2014 via gill net from Canadarago Lake (Otsego County, New York), then dissected and examined for intestinal parasites. One C. commersoni , collected from a tributary of Otsego Lake (Otsego County, New York), was used as a control in this study because it was not infected with intestinal helminths. Upon dissection, damage to the fish intestine was macroscopically visible, with the intestine perforated when infected with P. bulbocolli. Intestines observed to be infected with P. bulbocolli were opened with a longitudinal incision and fixed in neutral buffered formalin with the acanthocephalans remaining attached. Histological sections of intestine with P. bulbocolli attached were compared with histological sections of intestine in which no worms were present. Examination of sections revealed full penetration of the intestinal wall and tissue destruction to the mucosa, submucosa, stratum compactum, and circular and longitudinal muscle layers, as well as an extensive host immune response in the form of proliferation of cells at the sites of wounds. While these results were consistent with previous histopathological studies on this host and parasite species, the occurrence of pockets of hyaline degeneration in the muscularis reported here is a new finding for this host-parasite system, and it appears to be quite rare in the parasitological literature. It is hypothesized that the presence of hyaline degeneration may be related to secretion of trypsinlike proteins from the presoma of the acanthocephalan, a phenomenon suggested previously for the congener Pomphorhynchus laevis . The host-parasite interaction involving physical damage, secretion of enzymes, and an extensive host immune response may be the cause of the damage, but further research is needed to investigate the nature of these interactions.

Rhinebothrium jaimei sp. n. (Eucestoda: Rhinebothriidea: Rhinebothriidae): a new species from Neotropical freshwater stingrays (Potamotrygonidae).

Neotropical freshwater stingrays (Batoidea: Potamotrygonidae) host a diversity of parasites, including some, like their hosts, that are marine-derived. Among the parasites of potamotrygonids, the cestode fauna is the most diverse, with multiple genera having been reported, including genera endemic to the freshwaters of the Neotropics and genera that have cosmopolitan distributions. Recent efforts have been made to document the diversity of cestodes of this host-parasite system and to refine the taxonomy of parasite lineages. The present study contributes to our knowledge of Rhinebothrium Linton, 1890, a diverse cosmopolitan genus of rhinebothriidean cestode, with 37 species reported from marine batoids, one species from a freshwater stingray in Borneo and six species from potamotrygonids. Rhinebothrium jaimei sp. n. is described from two species of potamotrygonids, Potamotrygon orbignyi (Castelnau) (type host) and Potamotrygon scobina Garman, from Bahía de Marajó of the lower Amazon region. It can be distinguished from most of its marine congeners via multiple attributes, including its possession of two, rather than one, posteriormost loculi on its bothridia and the lomeniform shape of its bothridium that is wider anteriorly. In addition, R. jaimei sp. n. can be distinguished from the six Rhinebothrium species described previously from potamotrygonids based on a unique combination of morphological features. Despite extensive stingray cestode sampling efforts throughout all major Neotropical river systems, we found that unlike most species of potamotrygonid Rhinebothrium species, which are widespread, R. jaimei sp. n. is restricted to the Bahía de Marajó. The discovery of this new species of Rhinebothrium in Bahía de Marajó, an area in which potamotrygonids occur sympatrically with some species of euryhaline batoids (e.g. Dasyatis spp.) and share some trophic resources, suggest that modern ecological processes may be contributing to the distribution patterns of cestodes infecting potamotrygonids.

A new genus and species of cestode (Rhinebothriidea) from Mobula kuhlii (Rajiformes: Mobulidae) from Malaysian Borneo.

The cestode fauna of the shortfin devilray, Mobula kuhlii (Müller & Henle, 1841) was examined for the first time. The work resulted in the discovery of a new genus and species of rhinebothriidean tapeworm. Crassuseptum pietrafacei, n. gen. n. sp. is erected here on the basis of its unique scolex and proglottid morphology. Histological sections and examination by light and scanning electron microscopy demonstrated that this new genus differs from all other rhinebothriidean genera in its possession of bothridia in which the proximal and distal sides are confluent, i.e., not separated by a rim of tissue, and in its possession of testes that extend to the posterior margin of the ovary. This new species is characterized in part by its possession of stalked, elongate bothridia lacking lateral constrictions, with 13-15 prominent transverse bothridial septa and 4 reduced transverse septa, craspedote proglottids, each with 2-3 layers of testes in cross section, and a vas deferens that joins the cirrus sac at its anterior margin. Histological and optical sections through bothridial septa revealed that the transverse septa are formed by septal muscles separate from bothridial radial musculature, extending from the anterior side to the posterior side of each septum. This is only the second species rhinebothriidean cestode reported from mobulids. This study adds to the number of new species and genera of elasmobranch cestodes discovered off of the island of Borneo.

Diversification and species boundaries of Rhinebothrium (Cestoda; Rhinebothriidea) in South American freshwater stingrays (Batoidea; Potamotrygonidae).

BACKGROUND: Neotropical freshwater stingrays (Batoidea: Potamotrygonidae) host a diverse parasite fauna, including cestodes. Both cestodes and their stingray hosts are marine-derived, but the taxonomy of this host/parasite system is poorly understood. METHODOLOGY: Morphological and molecular (Cytochrome oxidase I) data were used to investigate diversity in freshwater lineages of the cestode genus Rhinebothrium Linton, 1890. Results were based on a phylogenetic hypothesis for 74 COI sequences and morphological analysis of over 400 specimens. Cestodes studied were obtained from 888 individual potamotrygonids, representing 14 recognized and 18 potentially undescribed species from most river systems of South America. RESULTS: Morphological species boundaries were based mainly on microthrix characters observed with scanning electron microscopy, and were supported by COI data. Four species were recognized, including two redescribed (Rhinebothrium copianullum and R. paratrygoni), and two newly described (R. brooksi n. sp. and R. fulbrighti n. sp.). Rhinebothrium paranaensis Menoret & Ivanov, 2009 is considered a junior synonym of R. paratrygoni because the morphological features of the two species overlap substantially. The diagnosis of Rhinebothrium Linton, 1890 is emended to accommodate the presence of marginal longitudinal septa observed in R. copianullum and R. brooksi n. sp. Patterns of host specificity and distribution ranged from use of few host species in few river basins, to use of as many as eight host species in multiple river basins. SIGNIFICANCE: The level of intra-specific morphological variation observed in features such as total length and number of proglottids is unparalleled among other elasmobranch cestodes. This is attributed to the large representation of host and biogeographical samples. It is unclear whether the intra-specific morphological variation observed is unique to this freshwater system. Nonetheless, caution is urged when using morphological discontinuities to delimit elasmobranch cestode species because the amount of variation encountered is highly dependent on sample size and/or biogeographical representation.

Intestinal helminths of freshwater stingrays in southeastern Peru, and a new genus and two new species of cestode.

Helminths of the spiral intestine of neotropical freshwater stingrays (Potamotrygonidae) were examined in Peru for the first time. The stingrays examined for helminths included Paratrygon aiereba, Potamotrygon motoro, and Potamotrygon cf. castexi. Present in P. aiereba were the cestodes Nandocestus guariticus (Marques, Brooks, and Lasso, 2001) n. gen. n. comb., Rhinebothrium copianullum n. sp., Rhinebothrium sp. 1, Rhinebothroides sp., Potamotrygonocestus cf. fitzgeraldae, and 1 species each of Cucullanus and Rhabdochona. Nandocestus n. gen. is erected to house N. guariticus, which is formally transferred from Anindobothrium Marques, Brooks, and Lasso, 2001. The new genus is unique among phyllobothriids in its possession of circummedullary vitelline follicles and a submarginal genital pore, in combination with bothridia with a single apical sucker and marginal bothridial loculi. The helminths of P. motoro included the cestodes Paraoncomegas araya, Acanthobothrium peruviense n. sp., Acanthobothrium cf. ramiroi, Rhinebothrium sp. 1, Rhinebothroides sp. 1, Potamotrygonocestus sp., the nematode Brevimulticaecum regoi, a species of Cucullanus, and a species of the digenean superfamily Diplostomoidea. The helminths of P. cf. castexi included the cestodes P. araya, N. guariticus n. gen. n. comb., Acanthobothrium cf. peruviense, Potamotrygonocestus sp., Rhinebothrium sp. 1, Rhinebothroides sp. 2, the nematode species Echinocephalus daileyi and B. regoi, 1 species each of Cucullanus, Rhabdochona, and Procamallanus, and a species of the digenean superfamily Hemiuroidea. All taxa were examined via light microscopy; the cestode taxa were also examined using scanning electron microscopy. Each helminth species recorded in this study is a first report from Peru. The study suggests that the diversity and host specificity of the cestodes in potamotrygonid stingrays may be greater than previously thought. The known numbers of genera and species of tetraphyllidean cestodes parasitizing neotropical freshwater stingrays are now 6 and 22, respectively.