First report of a fish blood fluke from sub-Saharan Africa: Nomasanguinicola dentata (Paperna, 1964) Warren and Bullard, 2023 infecting African sharptooth catfish, Clarias gariepinus (Burchell, 1822) Teugles, 1982 in the Kavango River, Namibia, and a revised phylogeny for Sanguinicolidae Poche, 1926.

We herein provide a supplemental description of Nomasanguinicola dentata (Paperna, 1964) Warren and Bullard, 2023 (Digenea: Sanguinicolidae) and provide a revised 28S phylogeny to test relationships among freshwater fish blood flukes. We examined the heart of three African sharptooth catfish, Clarias gariepinus (Burchell, 1822) Teugles, 1982 from the Kavango River (northeastern Namibia) that was infected with adults of N. dentata. This blood fluke differs from N. canthoensis by having a body 5.3-6.7 longer than wide (vs. 3.5-4.6), an anterior esophageal swelling 7-8% (vs. 14-24%) of total esophageal length, a posterior esophageal swelling 3-5% (vs. 8-10%) of total esophageal length, a pre-cecal (vs. wholly post-cecal) testis, and an ovary that does not extend laterally beyond the nerve cords. The 28S sequence for N. dentata differed from that of N. canthoensis by 144 bp (9% difference). The phylogenetic analysis recovered these species as sister taxa and Sanguinicolidae as monophyletic. This is the first report of a fish blood fluke from sub-Saharan Africa, and the first report of a species of Nomasanguinicola from Africa in ∼40 yrs.

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.

SYSTEMATIC REVISION OF THE FISH BLOOD FLUKES WITH DIAGNOSES OF CHIMAEROHEMECIDAE YAMAGUTI, 1971, ACIPENSERICOLIDAE N. FAM., SANGUINICOLIDAE POCHE, 1926, ELOPICOLIDAE N. FAM., AND APOROCOTYLIDAE ODHNER, 1912.

We herein morphologically diagnose the 5 natural groups of fish blood flukes and name them. Species of Chimaerohemecidae Yamaguti, 1971 infect chimeras, sharks, and rays (Chondrichthyes) and have C-shaped lateral tegumental spines and a non-sinusoidal testis or lack spines and have a sinusoidal testis. Species of Acipensericolidae n. fam. infect sturgeons and paddlefish (Acipenseriformes) and have a robust, bowl-shaped, pedunculate anterior sucker, lateral tegumental spines that are spike-like (not C shaped), an inverse U-shaped intestine (anterior ceca absent) with posterior ceca terminating near the excretory bladder, 6 testes (inter-cecal ovoid or oblong, lacking deep lobes; including 1 post-ovarian testis), a Laurer's canal, and a dextral common genital pore. Species of Sanguinicolidae Poche, 1926 infect primarily later-branching freshwater ray-finned fishes (Teleostei) and have a diminutive anterior sucker, a medial esophageal swelling (pouch), short, radial ceca of approximately equal length or short anterior ceca plus an elongate, dendritic posterior cecum, testis with appendix-like lateral lobes, no Laurer's canal, and separate or common genital pores. Species of Elopicolidae n. fam. infect ladyfishes, tarpons, and catadromous eels (Elopomorpha) and have a robust, bowl-shaped, pedunculate anterior sucker, lateral tegumental spines that are spike-like (can be lost in adult), short or indistinct anterior ceca, posterior ceca that terminate at level of the testis(es), a single testis or 2 testes, a Laurer's canal present or absent, and a sinistral common genital pore and atrium. Species of Aporocotylidae Odhner, 1912 primarily infect later-branching marine and estuarine ray-finned fishes (Teleostei) and have a spheroid anterior sucker with concentric rows of circumferential spines or the spheroid anterior sucker is lost in adults or adults have a diminutive anterior sucker, a sinuous esophagus lacking a pouch, an X- or H-shaped intestine having 4 ceca, long anterior ceca (or secondarily lost), smooth posterior ceca that extend posteriad in parallel with respective body margin and terminate near the posterior body end, testis(es) that lack appendix-like lateral lobes, no Laurer's canal, and a sinistral common genital pore or separate genital pores that are sinistral. Our 28S phylogeny recovered the fish blood flukes as monophyletic and each of the morphologically diagnosed families as monophyletic and sister to the remaining blood flukes infecting turtles and homeotherms. Acipensericolidae was recovered sister to the clade comprising Chimaerohemecidae + Sanguinicolidae and Elopicolidae + Aporocotylidae. The branching order and interrelationships of these families remains unsettled perhaps because of low taxon sampling among non-aporocotylids and extinction of intermediate taxa.

FIRST RECORD OF A PARASITE, DACTYLOGYRUS CF. SKRJABINI (MONOGENOIDEA: DACTYLOGYRIDAE), INFECTING INVASIVE SILVER CARP, HYPOPHTHALMICHTHYS MOLITRIX (VALENCIENNES, 1844) (CYPRINIFORMES: XENOCYPRIDIDAE) IN NORTH AMERICA.

The parasites infecting invasive carps in North America (all Cypriniformes: Xenocyprididae: grass carp, Ctenopharyngodon idella [Valenciennes, 1844]; silver carp, Hypophthalmichthys molitrix [Valenciennes, 1844]; bighead carp, Hypophthalmichthys nobilis [Richardson, 1845]; and black carp, Mylopharyngodon piceus [Richardson, 1846]) are little studied, and no parasite has been reported from silver carp there. We herein surveyed silver carp from Barkley Reservoir and Cheatham Reservoir (Cumberland River, Tennessee; June and December 2021) and the White River (Arkansas; May 2022) and collected numerous monogenoid specimens infecting the pores on the outer face of the gill raker plate. We heat-killed, formalin-fixed, and routinely stained some specimens for morphology and preserved others in 95% ethanol for DNA extraction and sequencing of the large subunit ribosomal DNA (28S). We identified our specimens as Dactylogyrus cf. skrjabini because they had a dorsal anchor deep root that is much longer than the superficial root, an approximately parallel penis and accessory piece, and a relatively large marginal hook pair V. No type specimen of Dactylogyrus skrjabiniAkhmerov, 1954 (type host and locality is silver carp, Amur River, Russia) is publicly available, but we borrowed several vouchers (NSMT-Pl 6393) that infected the gill rakers of silver carp captured in the Watarase River, Japan. The original description of D. skrjabini was highly stylized and diagrammatical, differing from the specimens we studied from North America and Japan by the dorsal anchor having a superficial root and shaft that comprise a strongly C-shaped hook (the superficial root curves toward the dorsal anchor point) (vs. superficial root straight, at ∼45° angle to deep root and directed away from the dorsal anchor point), a single, much reduced transverse bar that is narrow for its entire breadth (vs. dorsal and ventral transverse bars robust and broad, having an irregular outline), an accessory piece that lacks digitiform projections (vs. accessory piece with 4 digitiform projections), and an accessory piece that lacks a half cardioid-shaped process (vs. accessory piece having a half cardioid-shaped process). Our 28S sequences (generated from 4 specimens of D. cf. skrjabini: 2 from Tennessee [763 base pairs (bp)] and 2 from Arkansas [776 bp]) were identical to 1 ascribed to D. skrjabini from Japan. The present study is the first verifiable and credible report of a parasite from silver carp in North America and the first nucleotide information for a parasite from silver carp in North America.

FOREGUT ULTRASTRUCTURE OF ADULT SANGUINICOLA VOLGENSIS (RASÍN, 1929) MCINTOSH, 1934 (DIGENEA: APOROCOTYLIDAE).

Herein, we use scanning and transmission electron microscopy to describe the foregut (mouth, pharyngeal canal, and associated epithelia and musculature) of an adult freshwater fish blood fluke, Sanguinicola volgensis (Rasín, 1929) McIntosh, 1934, infecting the blood of sabre, Pelecus cultratus Linnaeus, 1758 (Cypriniformes: Leuciscidae) from the Volga River, Russia. Our results indicate that S. volgensis has a pharynx and lacks an oral sucker and that its pharyngeal canal acts as a peristaltic pump that sucks blood into the esophagus, whereupon digestion commences with granules secreted from the esophageal epithelium. We saw no evidence of longitudinal muscle fibers beneath the pharyngeal canal epithelium, pharyngeal glands, or pharyngeal epithelial cells or muscle cells within the pharyngeal muscular complex; collectively indicating the presence of a pharynx rather than an oral sucker. The specialized epithelial lining associated with the mouth and pharyngeal canal evidently is unique among neodermatans; it is smooth, ∼40 nm thick anteriorly, and thickens (∼250-700 nm) posteriorly as the mouth cavity transitions into the pharyngeal canal. The pharyngeal canal epithelium has lumps of dense material resembling those of the basal lamina and fibrous coat of the tegument. The actin-like material within the pharyngeal cavity epithelium could provide structural support to the pharynx.

Huffmanela cf. huffmani (Nematoda: Trichosomoididae) infecting swim bladder, peritoneum, and gonad of variable platyfish, Xiphophorus variatus (Cyprinodontiformes: Poeciliidae) and eastern mosquitofish, Gambusia holbrooki (Poeciliidae) in Florida; taxonomy, phylogenetic analysis, and pathological changes.

Variable platyfish, Xiphophorus variatus (Meek, 1904) (Cyprinodontiformes: Poeciliidae) and eastern mosquitofish, Gambusia holbrooki Girard, 1859 (Poeciliidae) from earthen ponds in west central Florida were examined for parasitic infections. At necropsy, we observed myriad nematodes (adults and eggs), which we identified as Huffmanela cf. huffmani, infecting the swim bladder, gonad, and visceral peritoneum. Nucleotide sequences (small subunit ribosomal DNA, 18S) of H. cf. huffmani from variable platyfish and eastern mosquitofish were identical; likewise for newly obtained 18S sequences of Huffmanela huffmani Moravec, 1987 from the swim bladder of red breast sunfish, Lepomis auritus (Linnaeus, 1758) (Centrarchiformes: Centrarchidae) and warmouth, Lepomis gulosus (Cuvier, 1829) from the San Marcos River (type locality for Huffmanela huffmani Moravec, 1987), Texas. The sequences of H. huffmani and H. cf. huffmani differed by 7 (1%) nucleotides. Pathological changes comprised proliferation of the tunica externa of the swim bladder in low-intensity infections in addition to inflammation, proliferation, and tissue necrosis of swim bladder, peritoneum, and gonad in high-intensity infections. The lesion was severe, affecting the cellular constituents of the swim bladder wall and reducing the size of the swim bladder lumen; potentially reducing swim bladder physiological efficiency. The present study is the first record of a freshwater species of Huffmanela Moravec, 1987 from beyond the San Marcos River, first record of a species of Huffmanela from a livebearer, first nucleotide sequences and phylogenetic analysis for Huffmanela, and first evidence that an infection by a species of Huffmanela causes pathological changes that could impact organ function.

OPECHONA CHLOROSCOMBRI AND OPECHONA CORKUMI N. SP. (DIGENEA: LEPOCREADIIDAE) FROM THE NORTHERN GULF OF MEXICO WITH PHYLOGENETIC ANALYSIS BASED ON 28S RDNA.

This study investigated the identity of 2 lepocreadiid digenean species belonging in the genus Opechona Looss, 1907 that infect littoral fishes of the northern Gulf of Mexico. Opechona chloroscombriNahhas and Cable, 1964, a species previously known only from the Caribbean Sea and the Atlantic Ocean off Brazil, is reported herein from the Atlantic bumper, Chloroscombrus chrysurus (L.), in the northern Gulf of Mexico. A second species infects the gulf butterfish, Peprilus burti Fowler, and the American harvestfish, Peprilus paru (L.), and it is described as a new species that occurs in coastal waters of the north-central and northeastern Gulf of Mexico. Metacercariae infecting the mesoglea of pelagic jellyfishes (Bougainvillia carolinensis [McCady], Chrysaora quinquecirrha [Desor], and Stomolophus meleagris Agassiz) and pelagic comb jellies (Mnemiopsis leidyi Agassiz and Beroe ovata Bruguière) were collected that resemble the new species but require further study to identify. Newly generated sequence fragments (28S rDNA) from both species of Opechona plus 2 other lepocreadiids collected during the study were aligned with publicly available sequences from 18 other lepocreadiids, 6 species of Aephnidiogenidae Yamaguti, 1934, and 2 species of Gorgocephalidae Manter, 1966. The alignment was subjected to Bayesian inference analysis rooted using a gorgocephalid. The resulting tree estimated the positions of both Opechona spp. as being unresolved within a group of taxa that included all available species of Opechona plus available species from the morphologically similar genera ProdistomumLinton, 1910, Preptetos Pritchard, 1960, and Clavogalea Bray, 1985. Although relatively similar in morphology, the 2 studied species of Opechona were surprisingly not closely related. Opechona cablei (Stunkard, 1980) Bray and Gibson, 1990 is herein considered to be a junior synonym of Opechona pyriformis (Linton, 1900) Bray and Gibson, 1990.

REDESCRIPTION OF CATHARIOTREMA SELACHII (MACCALLUM, 1916) JOHNSTON AND TIEGS, 1922 (MONOGENOIDEA: MONOCOTYLIDAE), EMENDATION OF MONOTYPIC CATHARIOTREMA JOHNSTON AND TIEGS, 1922, AND PROPOSAL OF CATHARIOTREMATINAE N. SUBFAM. BASED ON MORPHOLOGICAL AND NUCLEOTIDE EVIDENCE.

We herein redescribe the enigmatic Cathariotrema selachii (MacCallum, 1916) Johnston and Tiegs, 1922 based on the holotype, paratypes, and newly collected specimens infecting the olfactory organ of 5 shark species from the Gulf of Mexico (all new host records): scalloped hammerhead shark, Sphyrna lewini (Griffith and Smith, 1834) (Carcharhiniformes: Sphyrnidae); great hammerhead shark, Sphyrna mokarran (Rüppell, 1837); blacktip shark, Carcharhinus limbatus (Müller and Henle, 1839) (Carcharhiniformes: Carcharhinidae); spinner shark, Carcharhinus brevipinna (Müller and Henle, 1839); and Atlantic sharpnose shark, Rhizoprionodon terraenovae (Richardson, 1836) (Carcharhinidae). These specimens were morphologically indistinguishable from each other and from MacCallum's holotype and paratypes. Those sequenced had identical first internal transcribed spacer (ITS1) and large subunit ribosomal DNA (28S) nucleotide sequences. As such, C. selachii infects sharks of 2 orders (Carcharhiniformes, Lamniformes) and 3 families (Carcharhinidae, Sphyrnidae, Lamnidae) in the Northwestern Atlantic Ocean (type locality) and Gulf of Mexico (new records herein). This report is the first of new specimens of C. selachii in the Atlantic Ocean Basin in 95 yr and corrects long-standing error cascades and ambiguities concerning the morphology and systematic placement of C. selachii. Considering morphology and nucleotide-based phylogenetic evidence (28S, Bayesian analysis), we herein emend monotypic CathariotremaJohnston and Tiegs, 1922 and propose Cathariotrematinae Bullard n. subfam. for it and 4 other genera (all formerly assigned to Merizocotylinae Johnston and Tiegs, 1922). These genera comprise species infecting only the nose of sharks (monotypic Cathariotrema, SqualotremaKearn and Green, 1983 and SeptitremaKheddam, Chisholm, and Tazerouti, 2020 plus 3 species of TriloculotremaKearn, 1993) and nose of a chimaera (monotypic HolocephalocotyleDerouiche, Neifar, Gey, Justine, and Tazerouti, 2019). Cathariotrematinae differs from Merizocotylinae by having a 3-part attachment organ and by lacking open loculi that symmetrically encircle a cluster of >2 loculi in the center of the haptor. Monophyletic Cathariotrematinae (with sequences representing species of Cathariotrema, Triloculotrema, and Holocephalocotyle only) was sister to monophyletic Merizocotylinae, which together were sister to monophyletic Calicotylinae Monticelli, 1903. These subfamilies comprise a monophyletic group of monocotylids that have a double vagina and infect extrabranchial, enclosed niches (urogenital system, body cavity, olfactory chamber/nose) on their shark, ray, and chimaera hosts (all other monocotylids have a single vagina and infect the gill or body surfaces of rays only). Monocotylinae Taschenberg, 1879 and Decacotylinae Chisholm, Wheeler, and Beverley-Burton, 1995 were recovered as monophyletic. Heterocotylinae Chisholm, Wheeler, and Beverley-Burton, 1995 remained paraphyletic. We accept ParacalicotyleSzidat, 1970.

POSTHOVITELLINUM PSILOTERMINAE N. GEN., N. SP. (DIGENEA: LISSORCHIIDAE) INFECTING THE INTESTINE OF CYCLOCHEILOS ENOPLOS (CYPRINIFORMES: CYPRINIDAE) IN THE MEKONG RIVER, VIETNAM.

Herein we describe a new species and propose a new genus, Posthovitellinum psiloterminae n. gen., n. sp. (Lissorchiidae: Asymphylodorinae), based on specimens that infect the intestine of Cyclocheilos enoplos (Bleeker, 1849) (Cypriniformes: Cyprinidae), a migratory riverine carp from the Mekong River (Dong Thap province, Vietnam). The new species is assigned to Lissorchiidae by having a combination of features: spinous tegument, subterminal oral sucker, pre-equatorial ventral sucker, median and pretesticular ovary, submarginal genital pore at level of the ventral sucker, follicular vitellarium distributing in 2 lateral fields, and lacking eyespot pigment in the adult. It cannot be assigned to any existing asymphylodorine genus because it has the combination of a well-developed cirrus-sac, an unarmed ejaculatory duct and metraterm, a follicular vitellarium distributing in 2 lateral fields located between the posterior margin of the ventral sucker and the mid-level of the testis, and a sinistral, submarginal genital pore. The new species has an elongate, claviform cirrus-sac, a single, large, elongate-oval testis at the posterior extremity of the body, operculate eggs, and an I-shaped excretory bladder with secondary branches at the level of the testis and extending anteriad to the level of the pharynx. Bayesian inference analysis of the partial large subunit ribosomal DNA gene (28S rDNA) recovered the new species sister to Asaccotrema vietnamienseSokolov and Gordeev, 2019; these species differed by 118 nucleotides (12%; 983 bp fragment). This is the first lissorchiid reported from the Mekong River; only the second from southern Vietnam; and the fourth reported from a cyprinid fish in Vietnam. The aforementioned phylogenetic analysis included previously unpublished sequences representing lissorchiids infecting the intestine of North American suckers (Cypriniformes: Catostomidae): Lissorchis cf. nelsoni from spotted sucker; Minytrema melanops (Rafinesque, 1820) and Lissorchis cf. gullaris (immature) from smallmouth buffalo, Ictiobus bubalus (Rafinesque, 1818). Asymphylodora atherinopsidisAnnereaux, 1947, herein is treated as a species incertae sedis. The 28S tree topology suggests that Lissorchiinae may comprise more than 1 lineage, but additional species are needed to confidently assert this.

Fish blood flukes (Digenea: Aporocotylidae) from Indonesia: Two new genera and species infecting the banded eagle ray, Aetomylaeus nichofii (Bloch and Schneider, 1801) Capapé and Desoutter, 1979 (Myliobatiformes: Myliobatidae) from Borneo.

Specimens representing two new species of blood flukes (Digenea: Aporocotylidae), each representing a new genus, were collected from the banded eagle ray, Aetomylaeus nichofii (Bloch and Schneider, 1801) Capapé and Desoutter, 1979, in Borneo, Indonesia. Aetohemecus kirstenjensenae n. sp., n. gen. infected the heart of a banded eagle ray from Manggar, East Kalimantan, Borneo, Indonesia, and differs from its congeners by having an oviducal ampullae, an oötype posterior to all genitalia, and a uterus that extends anterior to the ovary. The new species resembles Selachohemecus spp., which infect requiem sharks (Carcharhinidae) in the Northwestern Atlantic Ocean and Gulf of Mexico, by having a single ventrolateral row of large C-shaped tegumental spines, X- or H-shaped intestine, and a post-caecal ovary. Specimens of Homestios janinecairae n. sp., n. gen. infected the heart of a banded eagle ray from Takisung, South Kalimantan, Borneo, Indonesia. The new species resembles other blood flukes that infect rays (Batoidea) by having a single, curving testis and an inverse U-shaped intestine as well as by lacking tegumental spines. It differs from all aporocotylids infecting batoids that lack spines by having a uterus that extends anteriad beyond the level of the seminal vesicle. The present study comprises the first record of an aporocotylid from Indonesia or from an eagle ray (Myliobatidae). To our knowledge, these are the first trematodes reported from a species of Aetomylaeus. The proposals of new genera and the description of two new species herein brings the total number of nominal chondrichthyan blood flukes to 13 species of 11 genera.

Two new species of Cephalogonimidae Looss, 1899 (Digenea: Plagiorchioidea) from Africa (Mozambique and Guinea), including a new phylogenetic hypothesis for related plagiorchioids.

Two new species of Cephalogonimidae Looss, 1899 (from Emoleptalea Looss, 1900 and Masenia Chatterji, 1933) are described from African freshwater fishes. Emoleptalea mozambiquensis n. sp. infected the turquoise killifish, Nothobranchius furzeri Jubb, in Mozambique and differs from its nine congeners by the combination of differences in body shape and size, oral sucker shape, sucker width ratio, configuration of the digestive tract and gonads, vitelline follicle shape and vitellarium configuration. Emoleptalea dollfusi Srivastava, 1960 is a synonym of Emoleptalea loossi Srivastava, 1960, thus there are still nine accepted species. Masenia baroensis n. sp. infected the globe fish, Tetraodon lineatus L., in the Republic of Guinea and differs from its five African congeners and 15 Asian congeners by the combination of circumoral spine count, oral sucker shape, caecal extent, ovary shape, genital pore position, and configuration of the vitellarium. Masenia dayali (Gupta & Puri, 1984) Chandra & Saxena, 2016 and Masenia pushpanjalii are nomina dubia. We propose Masenia ritai (Agrawal, 1964) n. comb., with M. ritai Sircar & Sinha, 1970 its junior synonym. Heterorchis cf. crumenifer (identified tentatively due to egg size) is reported from the West African lungfish, Protopterus annectens (Owen), in Mozambique (new geographical record). Heterorchis protopteri Thomas, 1958 and Heterorchis ghanensis Thomas, 1968 are species inquirendae. Sequences (28S rDNA) from these parasites were included in a Bayesian phylogenetic analysis with 37 other ingroup taxa. Both new species formed a clade with Masenia nkomatiensis Dumbo, Dos Santos & Avenant-Oldewage, 2019 from Africa. These three species formed a sister relationship with the other available cephalogonimids: Cephalogonimus americanus Stafford, 1902 and Cephalogonimus retusus (Dujardin, 1845), both frog parasites from North America and Europe, respectively. Heterorchis cf. crumenifer represented a distinct lineage within the Plagiorchioidea but formed a polytomy with species from 10 plagiorchioid families.

Redescription of the Type Species of Cardicola Short, 1953 (Digenea: Aporocotylidae) and Description of a New Congener Infecting Yellowedge Grouper, Hyporthodus flavolimbatus (Perciformes: Serranidae), from the Gulf of Mexico.

Cardicola Short, 1953 is the most speciose aporocotylid genus (35 species) and includes marine and estuarine species of fish blood flukes that infect "higher ray-finned fishes" (Euteleostei). Several clades within Cardicola are recovered in phylogenetic analyses of the large subunit ribosomal DNA (28S), but morphological synapomorphies for those nucleotide-based clades remain elusive. The type species, Cardicola cardiocola (Manter, 1947) Short, 1953, has not been recollected in 73 yr and the original description was incomplete; making a genus revision challenging because of the ambiguous systematic position of its type species. Herein, we redescribe C. cardiocola by using the holotype (USNM 1337732) and new specimens collected from the type host, jolthead porgy, Calamus bajonado (Sparidae), from nearby the type locality. It differs from its congeners by the combination of having a body that is 5 times longer than wide, an anterior sucker with concentric rows of spines, 2-6 tegumental body spines per row, an esophageal gland that is 22-43% of the esophageal length, a testis that is 3-5 times longer than wide and that fills the intercecal space, a vitelline duct connecting to the anterior aspect of the oötype, an ascending uterus that lacks any coil, a descending uterus yielding a single coil, an obvious cirrus sac separated by constriction from the seminal vesicle, a tegumental protrusion surrounding the terminal end of cirrus sac, and a male genital pore that is posterior to the remainder of the genitalia. We also describe a new congener infecting the heart of yellowedge grouper, Hyporthodus flavolimbatus (Serranidae), from the Gulf of Mexico. It differs from its congeners by the combination of having an anterior sucker that does not extend beyond the anterior body margin, 2-5 tegumental body spines per row, posterior ceca that are 9 times length of the anterior ceca and that lack any coil, a testis that is 3 times longer than wide and that does not fill the intercecal space, an ovary that is >60% of the body width, a vitelline duct that connects to the anterior aspect of the oötype, a uterus that is >10% of the body width and that extends posterior to all genitalia, and a rounded posterior body margin. It is the first species of Cardicola to be described from a grouper (Serranidae). The 28S and internal transcribed spacer 2 phylogenetic analyses recovered the new species as a distinct lineage within the clade of Cardicola spp.

An updated geographic distribution of Myxobolus cerebralis (Hofer, 1903) (Bivalvulida: Myxobolidae) and the first diagnosed case of whirling disease in wild-caught trout in the south-eastern United States.

Myxobolus cerebralis (Bivalvulida: Myxobolidae), the aetiological agent of salmonid whirling disease, was detected in 2 river basins of North Carolina during 2015, which initiated the largest spatial-temporal monitoring project for the disease ever conducted within the south-eastern United States (focused mainly in eastern Tennessee and western North Carolina). A total of 2072 rainbow trout Oncorhynchus mykiss, 1,004 brown trout Salmo trutta and 468 brook trout Salvelinus fontinalis were screened from 113 localities within 7 river basins during June 2017 through October 2019. Infections were detected by pepsin-trypsin digest, microscopy and the species-specific nested polymerase chain reaction (PCR) in 19 localities across 6 river basins. Myxospore morphology was indistinguishable from the published literature. In 2019, five rainbow trout that symptomatic for whirling disease (sloping neurocranium and lordosis) were captured and processed for histopathology. Myxospores were detected in the calvarial cartilage of two deformed trout with associated erosion of the cartilage consistent with reported whirling disease lesions. This is the first report of M. cerebralis in Tennessee and the first histologically confirmed cases of whirling disease in southern Appalachian (south-eastern United States) rivers and streams and expands the distribution of M. cerebralis throughout western North Carolina and eastern Tennessee.

A new genus and species of fish blood fluke, Achorovermis testisinuosus gen. et sp. n. (Digenea: Aporocotylidae), infecting critically endangered smalltooth sawfish, Pristis pectinata (Rhinopristiformes: Pristidae) in the Gulf of Mexico.

Achorovermis testisinuosus gen. et sp. n. (Digenea: Aporocotylidae) infects the heart of the smalltooth sawfish, Pristis pectinata Latham (Rhinopristiformes: Pristidae), in the eastern Gulf of Mexico. Specimens of the new genus, along with the other blood flukes that infect batoids are similar by having an inverse U-shaped intestine and a curving testis as well as by lacking tegumental spines. The new genus differs from all of the other blood flukes infecting batoids by having an elongate body (>50 × longer than wide), a testis having >100 curves, and an ovary wholly anterior to the uterus. It differs from Ogawaia glaucostegi Cutmore, Cribb et Yong, 2018, the only other blood fluke infecting a rhinopristiform, by having a body that is >50 × (vs <30 ×) longer than wide, a testis that is >75 × (vs <40 ×) longer than wide and has >100 (vs <70) curves, an ovary wholly anterior to (vs lateral and dorsal to) the seminal vesicle, a uterus wholly posterior to (vs overlapping and lateral to both) the testis and ovary, and a sinuous (vs convoluted) uterus. The new species joins a small group of chondrichthyan blood flukes that lack tegumental spines: O. glaucostegi, Orchispirium heterovitellatum Madhavi et Rao, 1970, Myliobaticola richardheardi Bullard et Jensen, 2008, Electrovermis zappum Warren et Bullard, 2019. Blood flukes infecting batoids are further unique by having a curving testis. That is, the blood flukes infecting species within Selachii are morphologically distinct from those infecting species within the Batoidea (excluding Gymnurahemecus bulbosus Warren et Bullard, 2019). Based on the morphological similarity, we suspect that the new species shares a recent common ancestor with O. glaucostegi. The discovery of the new species brings the total number of chondrichthyan blood flukes to 11 species assigned to nine genera.

First elucidation of a blood fluke (Electrovermis zappum n. gen., n. sp.) life cycle including a chondrichthyan or bivalve.

We describe a new fish blood fluke (Digenea: Aporocotylidae: Electrovermis zappum n. gen., n. sp.) and its life cycle in the intertidal zone adjacent to Mobile Bay (north-central Gulf of Mexico). This is the first elucidated aporocotylid life cycle that includes a chondrichthyan definitive host or a bivalve intermediate host. The new species undergoes asexual reproduction within the gonad of the variable coquina clam before maturing in the heart of the lesser electric ray. These adults and cercariae had identical 28S, 18S, and ITS2 nucleotide sequences. The new genus is similar to Ogawaia Cutmor et al., 2018 by having an inverse U-shaped intestine, a looping testis, and a uterus having distinct ascending and descending segments. It differs by having a body that is ≥ 30 × longer than wide, a testis with >30 curves, an obvious cirrus sac enveloping an extremely elongate cirrus, an ovary anterior to the seminal vesicle, and a post-gonadal uterus. The new species further differs from the type species of Ogawaia (Ogawaia glaucostegi Cutmore et al., 2018) by having a massive seminal vesicle (>10% of body length), a cirrus sac enveloping an extremely elongate cirrus, and a slightly sinuous uterus. Histology confirmed gametogenesis in an infected coquina clam but no discernible cellular response to infection was observed. We also i) characterize a second morphologically and genetically distinct cercaria (perhaps representing an innominate chondrichthyan aporocotylid) infecting the green jackknife clam in Mississippi Sound (north-central Gulf of Mexico), ii) compare all known aporocotylid cercariae infecting estuarine and marine mollusks and polychaetes and iii) provide a key to identify those cercariae. A phylogenetic analysis including nucleotide sequences from adult and cercarial specimens of the newly collected fish blood flukes further supports the notion that chondrichthyan aporocotylids are monophyletic and use bivalves as the first intermediate host; perhaps unlike any other blood fluke lineage.

New Genus and Species of Turtle Blood Fluke (Platyhelminthes: Digenea: Schistosomatoidea) Infecting Six-Tubercled Amazon River Turtles, Podocnemis sextuberculata (Pleurodira: Podocnemididae) from the Amazon River Basin (Peru).

Herein we describe a new species of turtle blood fluke (TBF) and propose a new genus to accommodate it, Pitiutrema revelae n. gen., n. sp. This blood fluke infects the heart of six-tubercled Amazon River turtles (Podocnemis sextuberculata [Cornalia, 1849] [Pleurodira: Podocnemididae]) in the headwaters of the Amazon River near Iquitos, Peru. It resembles the other 2 described species of South American freshwater TBFs (Atamatam amazoniensis Bullard and Roberts, 2019, and Paratamatam iquitosiensis Bullard and Roberts, 2019) by having a dorsoventrally flattened and ovoid body, an oral sucker with anteroventral spines, 2 inter-cecal testes arranged in a column, inter-gonadal terminal genitalia, an inter-cecal and post-ovarian Laurer's canal pore, and a Y-shaped excretory bladder. It differs from all other nominal TBFs by having the combination of an aspinose body that lacks mammillae, a tapered (not broadly rounded) posterior body end, a ventral sucker, slightly M-shaped or inverse U-shaped ceca, a deeply-lobed (dendritic) ovary, a transverse uterus, and a dispersed vitellarium. The new genus is further unique among TBF genera by having an anterior to posterior sequence of ventral sucker, anterior testis, ovary, cirrus sac (lateral to posterior half of ovary), and posterior testis. The phylogenetic results and placement of the new taxon (1) were both predicted by our morphological diagnosis and comparisons with related taxa, (2) further indicated monophyly of the nominal South American freshwater TBFs, (3) reaffirmed the marine derived lineage identity of the nominal South American freshwater TBFs, and (4) highlighted that the single cercarial sequence (TBF sp. W-810) from an ampullariid in Brazil does not share a recent common ancestor with any of the nominal South American freshwater TBFs. The new species is the eighth TBF reported from a side-necked turtle (Pleurodira), the first TBF from a member of Podocnemididae, and the third freshwater TBF from South America.

Pathobiology and first report of larval nematodes (Ascaridomorpha sp.) infecting freshwater mussels (Villosa nebulosa, Unionidae), including an inventory of nematode infections in freshwater and marine bivalves.

Little information is available on host-parasite relationships between bivalves and larval nematodes. Herein, we describe nematode larvae (likely stage 2) in the infraorder Ascaridomorpha infecting the foot, intestine, and mantle of a freshwater mussel (Alabama rainbow, Villosa nebulosa [Conrad, 1834]) and detail histopathological changes to infected tissues. A total of 43 live mussels from the South Fork of Terrapin Creek, Alabama, were collected between 2010 and 2014, with 14 sectioned for histopathology and 29 dissected. Of the 14 sectioned mussels, 5 appeared to be uninfected, and 7, 1, and 1 had histozoic infections observed in the foot and intestine, intestine only, and mantle edge and foot, respectively. Twenty-three of 29 (79%) of the mussels dissected were infected by live nematodes, and mean nematode abundance was 8.3 (CL = 5.23-13), with 2 mussels infected with >100 nematodes each. Thus, with a total of 32 of the 43 collected mussels observed with nematodes, overall infection prevalence was 74.4% (CL = 0.594-0.855). The 18S rDNA of this nematode was 99% similar to that of several ascaridids (species of Kathlaniidae Lane, 1914 and Quimperiidae Baylis, 1930) that mature in aquatic/semi-aquatic vertebrates; the recovered 18S phylogenetic tree indicated this nematode from V. nebulosa shares a recent common ancestor with Ichthyobronema hamulatum (Ascaridomorpha: Quimperiidae; GenBank Accession Number KY476351). Pathological changes to tissue associated with these infections comprised focal tissue damage, but a cellular response was not evident. The Alabama rainbow possibly represents an intermediate or paratenic host. Given these results, the nematode is likely not pathogenic under normal stream conditions; however, high intensity infections in the foot could inhibit pedal extension and retraction; which would have demonstrable health consequences to a freshwater mussel. Based on our review of the bivalve mollusc parasite literature, a collective biodiversity of 61 nematodes reportedly exhibit some degree of symbiosis (from commensal to parasitic) with 21 bivalves (28 nematode spp. from 17 marine bivalve spp.; 33 nematode spp. from 4 freshwater bivalve spp.); only four records exist of putatively parasitic nematodes from Unionida. The present study represents the first description of a nematode species that invades the tissues of a Unionidae species.

Neotropical Turtle Blood Flukes: Two New Genera and Species from the Amazon River Basin with a Key to Genera and Comments on a Marine-Derived Parasite Lineage in South America.

Two new genera and species of freshwater turtle blood flukes (TBFs) are described herein based on specimens infecting the nephritic and mesenteric blood vessels of "matamatas" (a side-necked turtle, Chelus fimbriata [Schneider, 1783] [Pleurodira: Chelidae]) from the Amazon River Basin, Peru. These taxa comprise the first-named species and the first-proposed genera of freshwater TBFs from the continent of South America. A new comparison of all TBF genera produced 6 morphologically diagnosed groups that are discussed in light of previous TBF classification schemes and a novel phylogenetic hypothesis based on the nuclear large subunit ribosomal DNA (28S). Considering external and internal anatomical features, species of the new genera (Atamatam Bullard and Roberts n. gen., Paratamatam Bullard and Roberts n. gen.) are most similar to each other and are together most similar to those of several marine TBF genera. The 28S phylogenetic analysis supported the monophyly of all 6 morphologically diagnosed groups of genera. Most notably, the freshwater TBFs of South America comprise a derived group nested within the clade that includes the paraphyletic marine TBFs. Not surprisingly in light of morphology, another marine TBF lineage (Neospirorchis Price, 1934) clustered with the freshwater TBFs of Baracktrema Roberts, Platt, and Bullard, 2016 and Unicaecum Stunkard, 1925. Our results, including an ancestral state reconstruction, indicated that (1) freshwater TBFs have colonized marine turtles twice independently and that (2) the South American freshwater TBFs comprise a marine-derived lineage. This is the first evidence that TBFs have twice independently transitioned from a marine to freshwater definitive host. Marine incursion is considered as a possible mechanism affecting the natural history of marine-derived freshwater TBFs in South America. A dichotomous key to accepted TBF genera is provided.

First Record of A Species of Mermithidae Braun, 1883 Infecting a Decapod, Palaemon paludosus (Palaemonidae).

The hemocoel of 26 of 30 (86%) eastern grass shrimps, Palaemon paludosus (Gibbes, 1850) (Decapoda: Palaemonidae), captured during June 2017 from several freshwater lakes near Leesburg and Lake Kissimmee, Florida, was infected by juveniles of a nematode species (Mermithidae sp.). Some infected eastern grass shrimps were preserved whole for histopathology, whereas others were dissected to excise parasitic juvenile nematodes, and still others were kept alive in glass aquaria such that post-parasitic (emerged) juvenile nematodes could be opportunistically observed alive and ultimately preserved. Parasitic and post-parasitic juvenile nematodes had cuticle cross-fibers, cephalic papillae, cup-shaped amphids, a horn-shaped vagina, a trophosome, and a caudal appendage, which collectively diagnosed them as Mermithidae sp. They differed from those of nematomorphs (Nematomorpha) by lacking 4 giant cells anteriorly, tegumental bristles, scale or plate-like areoles, a bifurcate or trifurcate posterior end, and an anus. A phylogenetic analysis of the small subunit rDNA (18S) that included all of the available mermithid sequences corresponding to morphologically diagnosed specimens recovered Mermithidae sp. within the clade of mermithids and sister to Ovomermis sinensis Chen, Jian, and Ren, 1991 . This is the first record of a mermithid infection in a decapod and first report of a mermithid infection in an aquatic crustacean from North America (another mermithid infects a terrestrial isopod there). The high prevalence of infection and the multiple geographic localities harboring infected eastern grass shrimps indicated that these infections were not spurious. Because no other decapod is confirmed as a mermithid host, we suspect that these specimens likely represent a new species with a life cycle worth studying, since none for a mermithid involving a decapod nor a crustacean has been elucidated to date. We also provide a table of all mermithid and nematomorph infections in crustaceans.

Gymnurahemecus bulbosus gen. et sp. nov. (Digenea: Aporocotylidae) infecting smooth butterfly rays, Gymnura micrura (Myliobatiformes: Gymnuridae) in the northern Gulf of Mexico, with a taxonomic key and further evidence for monophyly of chondrichthyan blood flukes.

Gymnurahemecus bulbosus gen. et sp. nov. infects the heart of smooth butterfly rays, Gymnura micrura in the Gulf of Mexico. Gymnurahemecus differs from all other accepted aporocotylid genera by having one column of C-shaped lateral tegumental spines, a medial oesophageal bulb anterior to a diverticulate region of the oesophagus, inverse U-shaped intestinal caeca, a non-looped testis, an oviducal ampulla, a Laurer's canal, and a post-caecal common genital pore. The new species, the shark blood flukes (Selachohemecus spp. and Hyperandrotrema spp.), and the chimaera blood fluke Chimaerohemecus trondheimensis are unique by having C-shaped lateral tegumental spines. Selachohemecus spp. and the new species have a single column of lateral tegumental spines, whereas Hyperandrotrema spp. and C. trondheimensis have 2-7 columns of lateral tegumental spines. The new species differs from Selachohemecus spp. most notably by having an inverse U-shaped intestine. The other ray blood flukes (Orchispirium heterovitellatum, Myliobaticola richardheardi, and Ogawaia glaucostegi) differ from the new species by lacking lateral tegumental spines, a medial oesophageal bulb, and a Laurer's canal and by having a looped testis. Phylogenetic analysis using large subunit ribosomal DNA (28S) indicated that the new species is sister to the clade that includes the other sequenced adult blood fluke (O. glaucostegi), which infects a ray in Australia. These results agree with and extend previous morphology- and nucleotide-based phylogenetic assertions that the blood flukes of early-branching jawed craniates (Chondrichthyes) are monophyletic and phylogenetically separated from the blood flukes of later-branching ray-finned fishes (Actinopterygii: Euteleostei).