Resurrection and emendation of Pseudoparamacroderoides Gupta & Agrawal, 1968 (Digenea: Macroderoididae), description of a new species from Vietnam, and comments on the systematics of macroderoidid genera.

We herein resurrect and emend Pseudoparamacroderoides Gupta & Agrawal, 1968 (Digenea: Macroderoididae) and describe a new species, Pseudoparamacroderoides dongthapensis n. sp., from adult specimens infecting the intestine of a riverine catfish, Mystus mysticetus Roberts, (Siluriformes: Bagridae) in the Mekong River, Vietnam. Pseudoparamacroderoides (Pseudoparamacroderoides seenghali Gupta & Agrawal, 1968 [type species]; Pseudoparamacroderoides vittati Kakaji, 1969 [= Ps. vittatusi]; Pseudoparamacroderoides raychaudhurii Agarwal & Kumar, 1983; and Pseudoparamacroderoides keni Agarwal & Agarwal, 1984) differs from other macroderoidid genera by having the combination of a subspherical oral sucker that lacks distinctly-enlarged circumoral spines; caeca that extend posteriad beyond the testes without forming a cyclocoel; testes that are approximately ≤1/3 maximum body width in diameter; a cirrus sac that is claviform, slightly dorsal to and predominantly lateral to the ventral sucker (cirrus sac partially dorsolateral to dextral or sinistral margin of ventral sucker); symmetrical vitelline fields that extend posteriad to the middle of the post-testicular space (not restricted to the inter-gonadal space) and that remain separate (not confluent) anteriorly and posteriorly; and an excretory vesicle that is I-shaped (with or without anterior swelling) and wholly post-ovarian, inter-testicular, or median to the posterior testis. Pseudoparamacroderoides dongthapensis n. sp. differs from its congeners by having an elongate hindbody (>2× forebody length) and an excretory vesicle that is approximately half as long as the body and that extends anteriad beyond the anterior testis. This is the first record of a species of Pseudoparamacroderoides from beyond the Indian sub-continent, from M. mysticetus, and from the Mekong River or from Vietnam. A diagnostic key to macroderoidid genera and a key to Pseudoparamacroderoides spp. are provided.

White spot syndrome virus in decapods from Mississippi Sound, USA, and susceptibility of Palaemonetes pugio and Uca panacea to a Chinese isolate.

The presence and quantity of white spot syndrome virus (WSSV) was surveyed using TaqMan real-time PCR to assess the extent of the virus in Mississippi Sound, USA. A total of 3577 wild decapods comprising 11 species was collected between November 2012 and August 2015: WSSV was present in 10 of the 11 species. Prevalence ranged from 5.1% in Uca rapax to 38.8% in U. spinicarpa. Viral load ranged from 1.8 to 7.3 log10 copies of WSSV µg-1 total DNA. Two Gulf species, Palaemonetes pugio and U. panacea, were injected with a series of doses of a virulent WSSV isolate from China to determine relative susceptibility and virulence because continuing translocation of highly pathogenic isolates of WSSV poses risk to native species. Survival was 0-65% for P. pugio and 5-60% for U. panacea. Median survival time was lower for P. pugio than U. panacea at all doses. Mean (±SD) lethal load was 9.0 ± 8.9 log copies of WSSV µg-1 total DNA in P. pugio and 8.2 ± 8.3 in U. panacea. Mean viral load in survivors was higher in U. panacea than in P. pugio (5.8 ± 6.1 vs. 3.2 ± 3.0 log copies of WSSV µg-1 total DNA); mean viral load was lower in wild individuals of those species (2.9 ± 3.2 for P. pugio and 4.9 ± 5.0 for U. panacea). U. panacea is potentially more tolerant of WSSV than P. pugio and may serve as an important reservoir host in the community.

White spot syndrome virus (WSSV) in cultured juvenile blue crabs Callinectes sapidus: oral versus injection exposure, and feeding frequency effects.

The efficacy of oral versus injection exposure and the effect of feeding frequency on the transmission of white spot syndrome virus (WSSV) in cultured juvenile blue crabs Callinectes sapidus were investigated. Crabs in Group 1 (G-1, n = 48) were exposed once orally to 100 mg of WSSV-infected shrimp tissue mg-1 of body weight (BW). The oral inoculum contained 2.6 × 109 WSSV genome copies mg-1 tissue. Group 2 (G-2, n = 46) received the same dosage once weekly for 5 wk. Group 3 (G-3, n = 12) was injected with 0.01 ml (2.6 × 107 genome copies 0.01 ml-1) WSSV inoculum g-1 BW. Group 4 (G-4, n = 12) was injected with 0.01 ml WSSV-negative shrimp serum and saline mixture g-1 BW. Dead and moribund animals were frozen at -80°C. After 37 d, all remaining crabs were frozen. Genomic DNA from gill tissue was evaluated for the presence and quantity of WSSV using TaqMan real-time PCR. All G-3 animals died and tested positive. No G-4 animals died or tested positive. In the fed groups, WSSV prevalence was approximately 16%, but viral load was higher and survival was lower in G-2 compared to G-1. Injected animals carried a higher viral load than fed animals, and dead animals had higher viral loads than live animals. Blue crab juveniles are susceptible to WSSV, but oral exposure does not efficiently transmit WSSV in juvenile blue crabs. Some animals can die from WSSV if repeatedly exposed.

Trematode diversity in freshwater fishes of the Globe II: 'New World'.

We provide a summary overview of the diversity of trematode parasites in freshwater fishes of the 'New World', i.e. the Americas, with emphasis on adult forms. The trematode fauna of three regions, South America, Middle America, and USA and Canada (North America north of Mexico), are considered separately. In total, 462 trematode species have been reported as adults from the Americas. The proportion of host species examined for parasites varies widely across the Americas, from a high of 45% in the Mexican region of Middle America to less than 5% in South America. North and South America share no adult species, and one exclusively freshwater genus, Creptotrema Travassos, Artigas & Pereira, 1928 in the Allocreadiidae Looss, 1902 is the most widely distributed. Metacercariae of strigeiforms maturing in fish-eating birds (e.g. species of the Diplostomidae Poirier, 1886) are common and widely distributed. The review also highlights the paucity of known life-cycles. The foreseeable future of diversity studies belongs to integrative approaches and the application of molecular ecological methods. While opportunistic sampling will remain important in describing and cataloguing the trematode fauna, a better understanding of trematode diversity and biology will also depend on strategic sampling throughout the Americas.

An additional genus and two additional species of Forticulcitinae (Digenea: Haploporidae).

Forticulcita platana sp. n. and Forticulcita apiensis sp. n. are described from Mugil liza Valenciennes in Argentina, and from Mugil cephalus Linnaeus in Salt Springs, Florida, USA, respectively. Supplemental material relating to the hermaphroditic sac of Forticulcita gibsoni Blasco-Costa, Montero, Balbuena, Raga et Kostadinova, 2009 is provided from a specimen isolated from M. cephalus off Crete, Greece. Forticulcita platana can be distinguished from all species of Forticulcita Overstreet, 1982 except F. gibsoni, based on possessing small pads or gland cells along the hermaphroditic duct. It can be differentiated from that species in possessing a hermaphroditic sac that is one and a half to two times longer than wide rather than one that is approximately three times longer than wide, longer eggs (44-52 µm rather than 34-44 µm long) and a shorter post-testicular space (< 45% of the body length). Forticulcita apiensis can be differentiated from the other species of Forticulcita in possessing a testis that is shorter than or equal to the pharynx rather than one that is longer than the pharynx. Xiha gen. n. is erected for Dicrogaster fastigatus Thatcher et Sparks, 1958 as Xiha fastigata (Thatcher et Sparks, 1958) comb. n., and we tentatively consider Dicrogaster fragilis Fernández Bargiela, 1987 to be Xiha fragilis (Fernández Bargiela, 1987) comb. n. The new genus fits within the concept of Forticulcitinae Blasco-Costa, Balbuena, Kostadinova et Olson, 2009 in having a vitellarium comprised of a single elongate to subspherical mass. Xiha can be differentiated from Forticulcita in having spines lining the hermaphroditic duct, or intromittent organ. A Bayesian inference analysis of partial 28S rDNA sequences of the two New World species of Forticulcita, Xiha fastigata and previously published haploporids places Xiha fastigata within the Forticulcitinae and sister to Forticulcita. Amended diagnoses for the subfamily and for Dicrogaster Looss, 1902 are provided.

Prosthenystera oonastica n. sp. (Digenea: Callodistomidae) from ictalurid catfishes in southeastern United States and molecular evidence differentiating species in the genus across Americas.

Prosthenhystera oonastica n. sp. is described as a cryptic species from the gall bladder of three ictalurid catfishes, Ictalurus punctatus (Rafinesque), Ictalurus furcatus (Valenciennes), and Pylodictis olivaris (Rafinesque), in rivers in the southeastern United States. The species was originally named by Wilmer A. Rogers in 1979 but never formally described. Material used for the description consists of two specimens of Roger's original material and ten new specimens. We found no significant morphological features that are useful for discriminating between the new species and its closest relative Prosthenhystera obesa (Diesing, 1850) Travassos, 1922 that occurs in the gall bladders of freshwater characiform, perciform and siluriform fishes, ranging from South America to southern Mexico. However, we found substantial differences in the large subunit ribosomal DNA (partial 28S rRNA gene) between the two species justifying the naming of the new species. Prosthenhystera oonastica n. sp. is readily differentiated from Prosthenhystera caballeroi Jiménez-Guzmán, 1973 that occurs in the gall bladders of characid fishes in Central America and Mexico, by having a relatively straight or bent rather than highly convoluted oesophagus, a relatively smaller ovary, smaller and less coalesced vitelline follicles, narrower caeca and smaller eggs. Comparison of ribosomal DNA (partial ITS1, 5.8S, ITS2, and partial 28S gene) between P. oonastica n. sp. and P. caballeroi revealed large differences between the two species. Phylogenetic analysis based on partial 28S rRNA gene sequences from the three studied species of Prosthenhystera Travassos, 1922 and related digenean taxa revealed a closer relationship between P. oonastica n. sp. and P. obesa than either has had with P. caballeroi.

Levisunguis subaequalis n. g., n. sp., a tongue worm (Pentastomida: Porocephalida: Sebekidae) infecting softshell turtles, Apalone spp. (Testudines: Trionychidae) in the southeastern United States.

A new tongue worm (Pentastomida) belonging to the Sebekidae Sambon, 1922 (Porocephaloidea Sambon, 1922) is described based on exemplars collected from softshell terrapins Apalone spinifera aspera (Agassiz) and Apalone ferox (Schneider) in the southeastern United States; a new genus is erected to accommodate the new species. The new species belongs in the Sebekidae because adults possess four simple hooks arranged in a trapezoid pattern on the ventral surface of the cephalothorax, a mouth opening between the anterior and posterior pairs of hooks, a terminal anus, an elongated uterus with preanal uterine pore, and a Y-shaped seminal vesicle. Nymphs possess geminate hooks, and the new species has an aquatic life-cycle in which nymphs become encapsulated in the body cavity of a freshwater fish and mature in the lungs of a terrapin. The new genus is distinct from other genera in the Sebekidae primarily by differences in hook morphology and the fact that representatives use a terrapin as a definitive host. Nymphs infecting fish and presumed to be the new species matured as postlarval juveniles conspecific with the new species when they were fed to the eastern mud turtle, Kinosternon subrubrum (Lacépède). Nymphs of the new species are anatomically similar to but larger than nymphs of Sebekia mississippiensis Overstreet, Self & Vliet, 1985 found in the mesentery of fishes captured in Florida, U.S.A. Adults of the new species differ from those of S. mississippiensis based on hook features, chloride cell pore pattern on annuli, body size, and use of a turtle rather than crocodilian definitive host. The new species is the third North American member of the Sebekidae.

Phylogenetic relationships of the Gorgoderidae (Platyhelminthes: Trematoda), including the proposal of a new subfamily (Degeneriinae n. subfam.).

Phylogenetic analyses of a range of gorgoderid trematodes based on ITS2 and partial 28S rDNA data lead us to propose the Degeneriinae n. subfam. for the genus Degeneria in recognition of its phylogenetic isolation and distinctive morphology and biology. The current concepts of the subfamilies Anaporrhutinae and Gorgoderinae were supported. Within the Gorgoderinae, the large genus Phyllodistomum is shown to be paraphyletic relative to Pseudophyllodistomum and Xystretrum. Notably, the clade of marine Phyllodistomum does not form a clade with the other marine genus, Xystretrum. Distinct clades within the Gorgoderinae correspond variously to identity of first intermediate host, form of cercaria and their marine or freshwater habitat. We are not yet in a position to propose separate genera for these clades.

Hirudinella ventricosa (Pallas, 1774) Baird, 1853 represents a species complex based on ribosomal DNA.

Digeneans in the genus Hirudinella de Blainville, 1828 (Hirudinellidae) from three species of pelagic fishes, Acanthocybium solandri (Cuvier), Makaira nigricans Lacépède and Thunnus albacares (Bonnaterre), and one benthic fish, Mulloidichthys martinicus (Cuvier), from the Gulf of Mexico are investigated using comparison of ribosomal DNA. Four species are identified based on molecular differences: Hirudinella ventricosa (Pallas, 1774) Baird, 1853 from A. solandri, Hirudinella ahi Yamaguti, 1970 from T. albacares, and two unidentified but distinct species of Hirudinella, herein referred to as Hirudinella sp. A (from both M. nigricans and M. martinicus) and Hirudinella sp. B from M. nigricans. Additionally, H. ahi, based tentatively on morphological identification, is reported from Thunnus thynnus (Linnaeus). This represents the first record of a hirudinellid from M. martinicus and the first record of H. ahi from T. thynnus. A phylogeny of some Hemiurata Skrjabin & Guschanskaja, 1954 using partial fragments of the 28S rDNA sequences is consistent with earlier phylogenies and the position of the Hirudinellidae Dollfus, 1932 is well-supported as a derived group most closely related to the Syncoeliidae Looss, 1899.

MOLECULAR CHARACTERIZATION OF SPOROCYSTS AND CERCARIAE (DIGENEA: BUCEPHALIDAE) INFECTING THE EASTERN OYSTER CRASSOSTREA VIRGINICA FROM VIRGINIA.

The identity of a larval bucephalid infecting the eastern oyster, Crassostrea virginica (Gmelin, 1791), from a tidal river in Virginia is investigated using ribosomal deoxyribonucleic acid (rDNA). The internal transcribed spacer (ITS1, 5.8S, ITS2) region and a portion of the 28S rDNA were isolated from genomic DNA from sporocysts containing cercariae and compared with sequences from GenBank and from our previous collections of possibly related bucephalids. The studied larval bucephalid was 100% identical at the ITS1, 5.8S, and partial 28S rDNA sequences with Prosorhynchoides paralichthydis (Corkum, 1961) Curran and Overstreet, 2009; however, it differed from P. paralichthydis by 6 bases plus 3 deletions in the ITS2 region. This level of variation at the ITS2 region has been demonstrated among some Indo-Pacific species of Prosorhynchoides Dollfus, 1929, suggesting that the larval bucephalid represents an unidentified or innominate species of Prosorhynchoides that is closely related to P. paralichthydis.

ENCYCLOBREPHUS BREVIVITELLUS N. SP. (DIGENEA: PLAGIORCHIOIDEA, INCERTAE SEDIS) INFECTING THE MEKONG SNAIL-EATING TURTLE, MALAYEMYS SUBTRIJUGA, IN THE MEKONG RIVER, VIETNAM, WITH PHYLOGENETIC ANALYSES BASED ON RDNA.

A new digenean species belonging in EncyclobrephusSinha, 1949 is described, and the generic diagnosis is amended to accommodate variation in several features of the new species. Worms were collected from the intestines of 2 specimens of the Mekong snail-eating turtle, Malayemys subtrijuga (Schlegel and Müller, 1845). Permanent whole-mounted worms were studied using light microscopy, and ribosomal DNA (rDNA) sequences were generated from 3 worms. We investigated the phylogenetic relationship of the new species among some digenea using separate Bayesian inference analyses, 1 based on the 28S rDNA gene and rooted using a species from the Monorchioidea Odhner, 1911, and a second based on the internal transcribed spacer 1 region rooted by a species in the Microphalloidea Ward, 1901. Prior to the analyses, Encyclobrephus was classified in the Encyclometridae Mehra, 1931. Previous studies using rDNA from the type species for the family, Encyclometra colubrimurorum (Rudolphi, 1819) Baylis and Cannon, 1924, have demonstrated that En. colubrimurorum is closely related to species of Polylekithum Arnold, 1934 in the Gorgoderoidea Looss, 1901. Nevertheless, phylograms from both analyses indicated that the new species of Encyclobrephus belongs in the Plagiorchioidea Lühe, 1901, related to species in the families Cephalogonimidae Looss, 1899, Plagiorchiidae Lühe, 1901, Reniferidae Pratt, 1902, and Telorchiidae Looss, 1899. The present results suggest that Encyclobrephus is not closely related to En. colubrimurorum. Familial classification of Encyclobrephus is contingent on molecular data availability for the type species but it should be removed from the Encyclometridae and classified as incertae sedis within the Plagiorchioidea. Encyclometridae belongs in the Gorgoderoidea, not the Plagiorchioidea.

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.

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.

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.

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.

The rise and fall of the ancient northern pike master sex-determining gene.

The understanding of the evolution of variable sex determination mechanisms across taxa requires comparative studies among closely related species. Following the fate of a known master sex-determining gene, we traced the evolution of sex determination in an entire teleost order (Esociformes). We discovered that the northern pike (Esox lucius) master sex-determining gene originated from a 65 to 90 million-year-old gene duplication event and that it remained sex linked on undifferentiated sex chromosomes for at least 56 million years in multiple species. We identified several independent species- or population-specific sex determination transitions, including a recent loss of a Y chromosome. These findings highlight the diversity of evolutionary fates of master sex-determining genes and the importance of population demographic history in sex determination studies. We hypothesize that occasional sex reversals and genetic bottlenecks provide a non-adaptive explanation for sex determination transitions.

Phylogenetic Affinities of Uvulifer Spp. (Digenea: Diplostomidae) in the Americas with Description of Two New Species from Peruvian Amazon.

Uvulifer Yamaguti, 1934, is a genus of diplostomoidean digeneans that parasitizes kingfishers worldwide. Species have a Neascus-type metacercaria that encysts in or on fish intermediate hosts, often causing black spot disease. Only 3 prior studies published DNA sequence data for Uvulifer species with only 1 including a single named species (Uvulifer spinatus López-Jiménez, Pérez-Ponce de León, & García-Varela, 2018). Herein we describe 2 new species of Uvulifer from the green-and-rufous kingfisher, Chloroceryle inda (Linnaeus), collected in Peru ( Uvulifer batesi n. sp. and Uvulifer pequenae n. sp.). Both new species are readily differentiated from their New World congeners by a combination of morphological characters including distribution of vitelline follicles and prosoma:opisthosoma length ratios. In addition, we used newly generated nuclear 28S rRNA and mitochondrial COI gene sequence data to differentiate among species and examine phylogenetic affinities of Uvulifer. This includes the 2 new species and Uvulifer ambloplitis (Hughes, 1927), as well as Uvulifer elongatus Dubois, 1988 , Uvulifer prosocotyle (Lutz, 1928), and Uvulifer weberi Dubois, 1985 , none of which have been part of prior molecular phylogenetic studies. Our data on Uvulifer revealed 0.1-2.2% interspecific divergence in 28S sequences and 9.3-15.3% in COI sequences. Our 28S phylogeny revealed at least 6 well-supported clades within the genus. In contrast, the branch topology in the COI phylogenetic tree was overall less supported, indicating that although COI sequences are a great tool for species differentiation, they should be used with caution for phylogenetic inference at higher taxonomic levels. Our 28S phylogeny did not reveal any clear patterns of host association between Uvulifer and particular species of kingfishers; however, it identified 2 well-supported clades uniting Uvulifer species from distant geographical locations and more than 1 biogeographic realm, indicating at least 2 independent dispersal events in the evolutionary history of the New World Uvulifer. Our results clearly demonstrate that the diversity of Uvulifer in the New World has been underestimated.

Two New Species of Saccocoelioides (Digenea: Haploporidae) with Phylogenetic Analysis of the Family, Including Species of Saccocoelioides from North, Middle, and South America.

Two cryptic species of haploporid digeneans belonging in Saccocoelioides are described from Costa Rica: one from a poeciliid fish, Poecilia gillii, and the other from a characid fish, Astyanax aeneus. Traditional morphological features are examined and found to be largely inefficient for differentiating among the new species and 20 New World congeners. Comparison of ribosomal DNA sequences among the 2 new species, 2 North American, 4 Middle American, and 3 South American species of Saccocoelioides, including the type-species Saccocoelioides nanii from Argentina and Saccocoelioides sogandaresi from Texas, is effective in differentiating among these species. A Bayesian inference analysis is conducted using a concatenated alignment of the same 2 ribosomal gene regions from 35 species belonging in the Haploporoidea and rooted by the atractotrematid Isorchis anomalus. The analysis provides stronger support for a close relationship between species in Saccocoelioides and Intromugil; thus, Intromugil is transferred from the Waretrematinae to the Chalcinotrematinae. Additionally, interrelationships among 11 species of Saccocoelioides are resolved and reveal a distinct genetic rift suggesting the presence of 2 distinct lineages within the genus, 1 containing the type-species and the other containing a group of species that more closely resemble other genera in the subfamily. Taxonomy of Saccocoelioides is discussed, and observations made during the present study justify taking several taxonomic actions: new combinations are proposed for Saccocoelioides tilapiae n. comb., formerly in the now-defunct Culuwiya, and Saccocoelioides ruedasueltensis n. comb., formerly in Chalcinotrema; Saccocoelioides guaporense nomen novem is proposed for Lecithobotrioides elongatus; Saccocoelioides papernai is considered a junior subjective synonym of Saccocoelioides overstreeti; Saccocoelioides godoyi is considered a junior subjective synonym of Saccocoelioides szidati; Saccocoelioides magnorchis and Saccocoelioides saccodontis are considered species inquirendae; and Saccocoelioides adelae is considered a nomen nudum. Four new hosts are reported for Saccocoelioides cichlidorum: Amphilophus lyonsi, Amatitlania nigrofasciatus, Amatitlania septemfasciatus, and Hypsophrys nicaraguensis. Molecular data call into question some existing species identifications in Saccocoelioides and reveal that molecular tools combined with traditional taxonomy are required for accurately identifying species in the genus. Twenty-two species of Saccocoelioides are formally accepted, but it is noted that as new molecular data become available, some of these species may be transferred to other genera in the subfamily.

On the systematics of some marine haploporids (Trematoda) with the description of a new species of Megasolena Linton, 1910.

Megasolena mikra sp. nov. is described from the queen angelfish, Holacanthus ciliaris (Linnaeus), off Florida, USA. The new species can be differentiated from all other species of Megasolena Linton, 1910 except Megasolena littoralis Muñoz, George-Nascimento, and Bray, 2017 in possessing testes that are smaller in diameter than the ovary. The new species can be differentiated from M. littoralis in lacking tegumental spines and possessing oral sucker papillae. Molecular data are provided for two species each of Cadenatella Dollfus, 1946, Hapladena Linton, 1910, and Megasolena Linton, 1910. Bayesian inference analysis of concatenated internal transcribed spacer region-2 (ITS2) and partial 28S rDNA sequences of 50 haploporoids revealed 1) a monophyletic Atractotrematidae Yamaguti, 1939 sister to the rest of the haploporoids tested; 2) a paraphyletic Megasoleninae Manter, 1935 - if Hapladena is included; and 3) a monophyletic Cadenatellinae Gibson and Bray, 1982 sister to the 'mugilid' haploporids. The 'mugilid' haploporids formed a monophyletic clade consisting of the subfamilies Chalcinotrematinae Overstreet and Curran, 2005, Forticulcitinae Blasco-Costa, Balbuena, Kostadinova, and Olson, 2009, Haploporinae Nicoll, 1914, and Waretrematinae Srivastava, 1937. Based on our analysis we restrict the Megasoleninae to include Megasolena, Vitellibaculum Montgomery, 1957, and Metamegasolena Yamaguti, 1970, all of which have species with two testes. To accommodate the former megasolenine taxa with a single testis, we erect the Hapladeninae subf. nov. for species in Hapladena and tentatively, Myodera Montgomery, 1957. Our results further support that haploporoids had a common marine ancestor with two testes, and that members of the Haploporoidea Nicoll, 1914 underwent diversification following a shift from a primarily marine life history with eupercarian hosts to a more euryhaline one with diadromous hosts (namely mullet).