The complete mitochondrial genome of 3 species of allocreadiids (Digenea, Allocreadiidae): characterization and phylogenetic position within the order Plagiorchiida.

Trematodes of the family Allocreadiidae are primarily found in the intestines of freshwater fishes around the world. The family includes 15 genera and c. 130 species. The last 2 decades have witnessed an increase in the genetic library of its species. Molecular data have been crucial for species delimitation and species description within Allocreadiidae and for understanding their evolutionary and biogeographical history and classification. Here, the mitogenomes of 3 species of allocreadiids were obtained using high throughput sequencing methods. Mitogenomes were compared with other members of the order Plagiorchiida to determine their molecular composition, gene rearrangement and phylogenetic interrelationships. The complete circular mitogenomes of Allocreadium lobatum, Creptotrematina aguirrepequenoi and Wallinia mexicana were 14 424, 13 769 and 13 924 bp long respectively, comprising 12 protein-coding genes, 22 transfer RNA genes, 2 ribosomal RNA genes and 2 non-coding regions. Gene arrangements were identical to other Xiphidiatan trematodes. Phylogenetic analyses using the mitogenomes revealed Allocreadiidae as a monophyletic group closely related to other members of the suborder Xiphidiata; A. lobatum was yielded as the sister taxon of C. aguirrepequenoi + W. mexicana. Our study increases the complete mitochondrial genome library of trematodes and strengthens our understanding of the phylogenetic relationships and classification of this parasite group.

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.

ERECTION OF BOTHRIOCESTUS N. GEN. (CESTODA: BOTHRIOCEPHALIDEA) AND REDESCRIPTION OF BOTHRIOCESTUS CUSPIDATUS (COOPER, 1917) (SYN. BOTHRIOCEPHALUS CUSPIDATUS) FROM WALLEYE, SANDER VITREUS, (PERCIFORMES: PERCIDAE) IN NORTH AMERICA.

Based on previous molecular phylogenetic analyses, Bothriocestus n. gen. is erected to accommodate bothriocephalid tapeworms that have an elongate scolex, a well-developed apical disc, and a narrow neck region, parasitize freshwater fishes in the Holarctic, and were previously placed in the polyphyletic genus Bothriocephalus Rudolphi, 1808 (Cestoda: Bothriocephalidea). Bothriocestus claviceps (Goeze, 1782) n. comb., a parasite of eels (Anguilla spp.) in the Holarctic region, is designated as the type species. Another species of the new genus, Bothriocestus cuspidatus (Cooper, 1917) (syn. Bothriocephalus cuspidatusCooper, 1917) is redescribed from type and voucher specimens, and new material from the type host, the walleye, Sander vitreus (Mitchill, 1818) (Perciformes: Percidae), in Manitoba and Ontario (where the type locality is located) (Canada) and in New York state and Wisconsin. Bothriocestus cuspidatus of S. vitreus is characterized primarily by the possession of a narrow, long strobila (total length up to 18 cm) composed of distinctly craspedote, trapezoidal proglottids, with primary, secondary, and tertiary proglottids differing in size, and by an arrow-shaped (=cuspidatus) scolex that is distinctly broader than the first proglottids, widest near the base in lateral view and gradually becoming broader toward the anterior end in dorsoventral view. A "dwarf" form of B. cuspidatus (total length of 9-27 mm) from Johnny darter, Etheostoma nigrum Rafinesque, 1820, and tessellated darter, Etheostoma olmstedi Storer, 1842 (both Percidae: Etheostominae), is also characterized morphologically in the present paper.

A NEW SPECIES OF BOTHRIOCEPHALUS (CESTODA: BOTHRIOCEPHALIDAE) FROM LEPOMIS SPP. (ACTINOPTERYGII: CENTRARCHIDAE) IN NORTH AMERICA.

Based on morphological and molecular data, a new species of tapeworm, Bothriocephalus kupermani n. sp., is described from pumpkinseed, Lepomis gibbosus (Linnaeus, 1758) (type host), and green sunfish, L. cyanellus Rafinesque, 1819 (Actinopterygii: Centrarchidae) in the United States. The new species differs from its North American congeners mainly in the shape of its scolex, which is almost rectangular in dorsoventral and lateral views (nearly parallel margins in the bothrial region), with shallow, wide bothria, and by an extensive field of vitelline follicles that are also variably present, albeit more sparsely, medially in the cortex of the ovarian and uterine areas. This tapeworm appears to be typically associated with Lepomis sunfishes. Examination of museum specimens of Bothriocephalus species from Lepomis spp. indicates that the tapeworm also parasitizes bluegill, Lepomis macrochirus, longear sunfish, Lepomis megalotis, and that previous records of Bothriocephalus cuspidatus and Bothriocephalus claviceps in these fishes are of the new species, B. kupermani.

A young parasite in an old fish host: A new genus for proteocephalid tapeworms (Cestoda) of bowfin (Amia calva) (Holostei: Amiiformes), and a revised list of its cestodes.

A new genus, Laruella n. gen., is proposed for the proteocephalid cestode L. perplexa (La Rue, 1911) n. comb. (syn. Proteocephalus perplexus La Rue, 1911), a parasite of a 'living fossil', the bowfin (Amia calva), in North America. The new genus is differentiated from other proteocephalid genera by having a massive four-lobed scolex without an apical organ and bearing suckers possessing tear-shaped sphincters on their inner rim, vitelline follicles forming L-shaped lateral fields, with the vitellarium turned inwards (medially) ventrally alongside the posterior margin of the ovary, a ring-like vaginal sphincter situated at a considerable distance from the genital atrium, and ellipsoid eggs resembling those of bothriocephalid and diphyllobothriid tapeworms, except for the absence of an operculum. Phylogenetic relationships of the new genus are not resolved, but it belongs to the so-called Neotropical clade of the Proteocephalidae, which is composed mainly of Neotropical tapeworms of siluriforms and other teleosts, but also Nearctic and Palaearctic species of Ophiotaenia La Rue, 1911 from snakes and amphibians. A morphologically similar species, Proteocephalus ambloplitis (Leidy, 1887) from bass (Micropterus spp.) in North America, is provisionally retained in Proteocephalus Weinland, 1858 because its relationships to L. perplexa are not yet clear. The former species differs from L. perplexa by the presence of a large apical organ, large, elongate vaginal sphincter situated near the genital atrium, vitelline follicles limited to lateral longitudinal fields, strongly coiled vas deferens within the cirrus sac, and a convoluted vaginal canal anterior to the ovarian isthmus. Laruella perplexa reportedly has a s broad spectrum of hosts but most are likely postcyclic or accidental hosts. A list of cestode parasites reported from bowfin is provided; it includes eight species and three taxa not identified to the species level. However, only three adult cestodes, L. perplexa and two species of Haplobothrium Cooper, 1914, are typical tapeworm parasites of bowfin, but previous molecular studies indicate possible existence of a putative new species in bowfin.

Host-Specific Parasites Reveal the History and Biogeographical Contacts of Their Hosts: The Monogenea of Nearctic Cyprinoid Fishes.

Host-specific parasites exhibit close co-evolutionary associations with their hosts. In the case of fragmented/disjunct host distribution, host-specific parasites may reflect the biogeographical history of regions and/or the role played by contacts of hosts. The present study was focused on Dactylogyrus (Monogenea) species almost exclusively parasitizing cyprinoid fishes. We investigated the phylogenetic relationships between Dactylogyrus parasites of Nearctic cyprinoids (Leuciscidae) and Dactylogyrus parasites of Palearctic cyprinoids and used Dactylogyrus phylogeny to explore the biogeography of fish hosts in Europe and North America. Phylogenetic analyses revealed that two Nearctic clades of Dactylogyrus spp. have different origins. Historical contacts between European and North American leuciscids were accompanied by the host switching of Dactylogyrus species. In the Nearctic region, Dactylogyrus parasites also colonized non-leuciscid fishes. Dactylogyrus spp. of three Nearctic leuciscid clades were included in the phylogenetic reconstruction; only Dactylogyrus spp. of the Plagopterinae had a common origin. Dactylogyrus species did not reflect the phylogenetic relationships among leuciscid clades, suggesting that past co-diversification was overshadowed by colonization events mediated by paleogeographic and climatological changes and extensive drainage reorganization. Host-specific monogeneans serve as a supplementary tool to reveal the historical biogeographical contacts between freshwater fish from the North America and Europe and also contemporary contacts of leuciscids in North America.

LOOP-MEDIATED ISOTHERMAL AMPLIFICATION (LAMP) ASSAY FOR DETECTION OF ASIAN FISH TAPEWORM, SCHYZOCOTYLE ACHEILOGNATHI (YAMAGUTI, 1934) [SYN. BOTHRIOCEPHALUS ACHEILOGNATHI].

The Asian fish tapeworm (Schyzocotyle acheilognathi syn. Bothriocephalus acheilognathi) (AFT) is an invasive parasite that can infect many species of fish, although most hosts are primarily members of Cyprinidae. Pathogenicity has most often been reported in aquaculture settings in fry and fingerling stages of carp (Cyprinus spp.). More recently, it has been shown to cause growth retardation in the endangered bonytail chub (Gila elegans) and found to be widespread in populations of endangered humpback chub (Gila cypha) in the Colorado River, Grand Canyon, Arizona. AFT spreads most often through the transport of infected fish, particularly baitfish. Despite its harmful potential, there is no efficient or accurate ante mortem test to detect AFT in water or fish samples before transport. Herein, we report on the development of a sensitive and specific loop-mediated isothermal amplification (LAMP) assay to detect the parasite in under 30 min from laboratory prepared samples. Six LAMP primers were designed to amplify a variable region of the 18S ribosomal RNA gene in AFT with the detection and quantification of DNA on a real-time fluorometer. The limit of detection was 1 × 101 copies/µl of DNA extracted from as few as 2 AFT eggs. Future application of our assay would be a low-cost test to rapidly and accurately detect AFT DNA from environmental samples on-site so that preventive actions can be taken to halt the spread of the AFT through the movement of infected fish.

Molecular evidence of three closely related species of Biacetabulum Hunter, 1927 (Cestoda: Caryophyllidea): a case of recent speciation in different fish hosts (Catostomidae)?

Monozoic tapeworms (Caryophyllidea) are dominant components of parasite communities of suckers (Catostomidae) in North America, with Biacetabulum Hunter, 1927 representing one of the more species-rich genera. Molecular (28S rDNA) and morphological (including scanning electron microscopy and histology) evaluation of newly collected tapeworms from different fish hosts revealed the existence of four similar (and three closely related) species of Biacetabulum. These four species differ from their congeners by having a long body (up to 48 mm long) with a very long, slender neck (its length represents ≥30% of total body length), a large, globular scolex with a prominent central acetabulum-like loculus on the dorsal and ventral sides, two pairs of shallow lateral loculi and a distinct, slightly convex apical disc, and a cirrus-sac that is situated between the anterior arms of the ovarian wings. Taken together, the morphological and molecular data and the host associations of these species provide evidence of their host specificity. Biacetabulum isaureae n. sp. occurs in notch clip redhorse, Moxostoma collapsum, in South Carolina (USA), B. longicollum n. sp. in silver redhorse, Moxostoma anisurum (type host), and golden redhorse, M. erythrurum, in Manitoba (Canada) and West Virginia (USA), B. overstreeti n. sp. in a spotted sucker, Minytrema melanops, in Mississippi, and B. hypentelii n. sp. in northern hogsucker, Hypentelium nigricans, in Tennessee (USA). The new species differ from each other in the number of postovarian vitelline follicles, the posterior extent of preovarian vitelline follicles and relative size of the cirrus sac.

The Proteocephalus species-aggregate (Cestoda) in cyprinoids, pike, eel, smelt and cavefish of the Nearctic region (North America): diversity, host associations and distribution.

Tapeworms (Cestoda) of the Proteocephalus-species aggregate from cyprinoids, pike, eel, smelt and cavefish in the Nearctic region (North America) are reviewed, based on a critical examination of newly collected and museum specimens. For some species neither new nor museum specimens were available and only literature data were used for these taxa. Two species occur in North American cyprinoids: (i) Nearctic Proteocephalus buplanensis Mayes, 1976 in Semotilus atromaculatus (Mitchill) in the upper Mississippi River and Hudson Bay drainage basins, and (ii) Holarctic P. torulosus (Batsch, 1786) (syns. P. ptychocheilus Faust, 1919; P. cobraeformis Haderlie, 1953; and Ophiotaenia critica Mpoame & Landers, 1981, new synonym), which occurs in Ptychocheilus spp. and other leuciscids in the western part of North America. Proteocephalus pinguis La Rue, 1911 is a specific parasite of pike (Esox spp.), which is briefly redescribed here to establish its diagnostic morphological characteristics because the original description was based on a mixture of at least two species. In addition to P. pinguis, pike serve as postyclic hosts of several species of the Proteocephalus-aggregate typical of other fish, such as bass, perch and whitefish, namely P. fluviatilis Bangham, 1925, P. pearsei La Rue, 1919 and P. longicollis (Zeder, 1800). Cavefish (Amblyopsidae) in North America harbour two endemic species, P. chologasteri Whittaker & Hill, 1968 from Chologaster agassizii Putman and P. poulsoni Whittaker & Zober, 1978 from Amblyopsis spelaea DeKay, which have never been found since their original description and their validity should be confirmed based on new collections and molecular data. Two other species of the Proteocephalus-aggregate, P. macrocephalus (Creplin, 1825), a parasite of eels (Anguilla spp.), and P. tetrastomus (Rudolphi, 1810) from smelt (Osmeridae), have circumboreal (Holarctic) distribution. Molecular data are available only for three of the seven species treated herein, but they do not form a monophyletic group.

Ex Uno Plures? Morphotype and Lineage Diversity of Bothriocephalus (Cestoda: Bothriocephalidea) in North American Freshwater Fishes.

Morphological and molecular evaluation of tapeworms of the genus Bothriocephalus Rudolphi, 1808 (Cestoda: Bothriocephalidea), based on newly collected and uniformly fixed worms from freshwater fishes in Canada and the United States has revealed unexpected diversity. With a combination of selected morphological features and 4 molecular markers (18S rDNA V8 region, ITS1, ITS2, and COI gene sequences), the following morphotypes and lineages of the Bothriocephalus cuspidatus Cooper, 1917 complex were identified, several of which are specific to their respective fish definitive hosts and may represent separate species: B. cuspidatus sensu stricto from walleye, Sander vitreus (type host), which likely includes a miniature morphotype from Johnny darter, Etheostoma nigrum (both Percidae); Bothriocephalus morphotype from pumpkinseed, Lepomis gibbosus (Centrarchidae); and Bothriocephalus morphotype from rock bass, Ambloplites rupestris (Centrarchidae). The Bothriocephalus morphotype from goldeye, Hiodon alosoides (Hiodontidae), may also represent a separate lineage (possibly Bothriocephalus texomensisSelf, 1954) but requires additional studies. A morphotype from smallmouth bass, Micropterus dolomieu, based on a single specimen, is morphologically and genetically very similar to the morphotype from rock bass. Morphological study of the scolex and strobila of heat-killed and fixed specimens has revealed consistent differences, often subtle, that allowed us to differentiate between these morphotypes.

The Proteocephalus species-aggregate (Cestoda) in sticklebacks (Gasterosteidae) of the Nearctic Region, including description of a new species from brook stickleback, Culaea inconstans.

A survey of the species of the Proteocephalus-aggregate from sticklebacks (Actinopterygii: Gasterosteidae) is provided. The occurrence of three species in North America is confirmed: (i) Proteocephalus filicollis (Rudolphi, 1802), which has been reported from the three-spined stickleback, Gasterosteus aculeatus Linnaeus, in the northeastern part of North America (Newfoundland); (ii) Proteocephalus pugetensis Hoff et Hoff, 1929 occurs also in G. aculeatus, but in northwestern North America (British Columbia and Washington); and (iii) Proteocephalus culaeae sp. n., which is described from the brook stickleback, Culaea inconstans (Kirtland), in Manitoba (Canada). Another species, Proteocephalus ambiguus (Dujardin, 1845), a specific parasite of the nine-spined stickleback, Pungitius pungitius (Linnaeus), and type species of the genus, has also been found in North America (Alberta, Canada), but its vouchers are in poor condition and cannot be reliable assigned to this species. Both species reported from three-spined stickleback differ from each other by the shape of the scolex (rounded in P. filicollis versus continuously tapered towards the anterior extremity in P. pugetensis) and the apical sucker (widely oval to subspherical in frontal view in P. filicollis versus flattened in P. pugetensis). Proteocephalus culaeae sp. n. is characterised by a short body composed of a few, continuously widened proglottids, a short scolex narrower than the strobila and devoid of an apical sucker, a short, pyriform cirrus sac, no vaginal sphincter, and few testes. A key to species of the Proteocephalus-aggregate from sticklebacks is provided.

Tapeworms (Cestoda) of Ictalurid Catfishes (Siluriformes) in North America: Redescription of Type Species of Two Genera and Proposal of Essexiellinae n. Subfam.

Ictalurid catfishes (Siluriformes) in North America harbor proteocephalid tapeworms of the subfamily Corallobothriinae. Type species of 2 of 3 genera of these tapeworms from ictalurids are redescribed, based on museum and newly collected material. Essexiella fimbriata (Essex, 1928) is typified mainly by a wide, umbrella-shaped scolex with a metascolex formed by numerous folds of tissue, anteriorly directed suckers without sphincters, vitellarium bent inwards posteriorly, "flower-shaped" uterus (with anterior, lateral, and posterior diverticula), and a conspicuously pre-equatorial genital atrium. Verified host records of this cestode are only from 3 species of Ictalurus Rafinesque, 1820. Megathylacoides giganteum (Essex, 1928), which seems to be specific to the channel catfish (Ictalurus punctatus), possesses a globular scolex, with a weakly developed metascolex formed by tissue folds posterior to the suckers, anterolaterally directed suckers with large semilunar sphincters, proglottids that are widest at the level of the genital atrium at the anterior third of the proglottid, and uterine diverticula that do not reach the vitelline follicles laterally. A new subfamily, Essexiellinae Scholz and Barcák, is proposed to accommodate species of EssexiellaScholz, de Chambrier, Mariaux and Kuchta, 2011 (type genus), MegathylacoidesJones, Kerley and Sneed, 1956, and CorallotaeniaFreze, 1965 from ictalurid catfishes in the Nearctic Region. These tapeworms possess a metascolex, medullary genital organs, uterus lined with numerous chromophilic cells, pre-equatorial genital atrium, and uterine development of type 2. The new subfamily was monophyletic in all molecular phylogenetic analyses, being most closely related to 3 Neotropical proteocephalids from the redtail catfish, Phractocephalus hemioliopterus (Bloch and Schneider, 1801), but distant from all remaining proteocephalid tapeworms from freshwater fishes in North America.

Odds ratios and hurdle models: a long-term analysis of parasite infection patterns in endangered young-of-the-year suckers from Upper Klamath Lake, Oregon, USA.

We used odds ratios and a hurdle model to analyze parasite co-infections over 25 years on >20,000 young-of-the year of endangered Shortnose and Lost River Suckers. Host ecologies differed as did parasite infections. Shortnose Suckers were more likely to be caught inshore and 3-5 times more likely to have Bolbophorus spp. and Contracaecum sp. infections, and Lost River Suckers were more likely to be caught offshore and approximately three times more likely to have Lernaea cyprinacea infections. An observed peak shift seems likely to be due to a lower host size limit for Bolbophorus spp. (13.6 mm) compared with L. cyprinacea (23.4 mm). The large data set allowed us to generate strong hypotheses: (i) that a major marsh restoration project had unintended consequences that resulted in an increase in infections; (ii) that co-infection with Bolbophorus spp. increased the odds of infection by L. cyprinacea and Contracaecum sp.; (iii) that significant declines in the odds of infection over approximately 25 days were due to parasite-induced host mortality; (iv) that the fish's small size relative to L. cyprinacea and Contracaecum sp. might be directly lethal; (v) that the absence of L. cyprinacea infections in the early 1990s was associated with good year-class production of the suckers; and (vi) that parasites might increase the odds of vagrancy from the nursery ground.

Scolex morphology of monozoic tapeworms (Caryophyllidea) from the Nearctic Region: taxonomic and evolutionary implications.

A comparative study of the scoleces of monozoic tapeworms (Cestoda: Caryophyllidea), parasites of catostomid and cyprinid fishes (Teleostei: Cypriniformes) in the Nearctic Region, was carried out using light and scanning electron microscopy. Scoleces of 22 genera of North American caryophyllideans were characterised and their importance for taxonomy, classification and phylogenetic studies was critically reviewed. Nearctic genera exhibit a much higher variation in the shape and form of scoleces compared with taxa in other biogeographical regions. The following basic scolex types can be recognised in Nearctic caryophyllideans: monobothriate (Promonobothrium Mackiewicz, 1968), loculotruncate (Promonobothrium, Dieffluvium Williams, 1978), bothrioloculodiscate (Archigetes Leuckart, 1878, Janiszewskella Mackiewicz et Deutsch, 1976, Penarchigetes Mackiewicz, 1969, Pseudoglaridacris Oros, Uhrovic et Scholz, 2018), fixomegabothriate (Capingens Hunter, 1927), bulbate and bulboacuminate (Atractolytocestus Anthony, 1958), cuneiloculate (Hypocaryophyllaeus Hunter, 1927, Rowardleus Mackiewicz et Deutsch, 1976, Spartoides Hunter, 1929), biacetabulate, bulboloculate, bothrioloculodiscate (Biacetabulum Hunter, 1927), tholate (Hunterella Mackiewicz et McCrae, 1962), cuneifimbriate (Khawia Hsü, 1935), cuneiform (Calentinella Mackiewicz, 1974, Caryophyllaeides Nybelin, 1922, Edlintonia Mackiewicz, 1970), hastate (Pseudolytocestus Hunter, 1929), loculotholate (Bialovarium Fischthal, 1953, Pliovitellaria Fischthal, 1951), and cuneiformoloculate (Glaridacris Cooper, 1920, Isoglaridacris Mackiewicz, 1965). The same type of scolex may be shared by species of different genera or families and species of the same genus can have a scolex of conspicuously different morphology, e.g. in Promonobothrium. Scolex morphology may be therefore of limited use in generic designation.

Amended diagnosis, validity and relationships of the genus Acrolichanus Ward, 1917 (Digenea: Allocreadiidae) based on the 28S rRNA gene, and observations on its lineage diversity.

Adult specimens of the allocreadiid trematode Acrolichanus auriculatus (Wedl, 1858) were collected from Acipenser schrenckii Brandt from the River Amur and Amur Estuary, Acipenser ruthenus L. from the Rivers Irtysh and Oka (Asian and European parts of Russia, respectively), and Acipenser fulvescens Rafinesque from Lake Winnebago, Wisconsin, USA, and used for phylogenetic analyses based on 28S rDNA sequence data. The results supported the monophyly of Acrolichanus populations from both continents and a clear separation of A. auriculatus from other allocreadiid taxa, thus supporting the validity of the genus Acrolichanus Ward, 1917. This study formally reestablishes the genus Acrolichanus. Species of this genus differ from other allocreadiids by the following combination of morphological features: triangular mouth opening with rounded posterior corners, simple ventral, dorsolateral and dorsomedian muscular lobes on the oral sucker, stout cirrus-sac, pars prostatica with dorsal pocket, and massive cirrus with conspicuous triradiate lumen when invaginated. Specimens of the trematode from North America and the Rivers Irtysh and Oka were more closely related to each other than to the specimens from River Amur and Amur Estuary. This reflects the evolutionary divergence among sturgeons into Pacific and Atlantic clades. The phylogenetic analyses also confirmed the paraphyly of the genus Crepidostomum Braun, 1900.

The Proteocephalus Species-Aggregate in Freshwater Centrarchid and Percid Fishes of the Nearctic Region (North America).

In the present paper, species of the Proteocephalus-aggregate de Chambrier, Zehnder, Vaucher, and Mariaux, 2004 (Cestoda: Proteocephalidae) reported from centrarchid and percid fishes in North America are reviewed, and their taxonomic status is critically assessed based on a study of type specimens and new material from Canada and the United States. The following 3 species, supposedly strictly specific to their fish definitive hosts, are recognized as valid: (1) Proteocephalus fluviatilis Bangham, 1925 (new synonyms Proteocephalus osburni Bangham, 1925 and Proteocephalus microcephalus Haderlie, 1953 ; Proteocephalus 'robustus' nomen nudum) from the smallmouth and largemouth bass, Micropterus dolomieu (Lacépède) (type host) and Micropterus salmoides (Lacépède) (both Centrarchidae); (2) Proteocephalus luciopercae Wardle, 1932 (new synonym Proteocephalus stizostethi Hunter and Bangham, 1933 ) from the walleye, Sander vitreus (Mitchill) (type host), and sauger, Sander canadensis (Griffith et Smith) (Percidae); and (3) Proteocephalus pearsei La Rue, 1919 , a parasite of the yellow perch, Perca flavescens Mitchill (Percidae). All species are illustrated based on new, properly heat-fixed material. Scanning electron micrographs of the scoleces of percid tapeworms P. luciopercae and P. pearsei, as well as the bass tapeworms P. fluviatilis and Proteocephalus ambloplitis ( Leidy, 1887 ), the latter of which does not belong to this Proteocephalus-aggregate, are provided for the first time together with a simple key to species identification of proteocephalids from centrarchiform and perciform teleost fishes.

Life Cycle of the Trout Cecal Nematode, Truttaedacnitis truttae (Nematoda: Cucullanidae): Experimental and Field Observations.

Truttaedacnitis truttae is a cucullanid nematode of primarily salmonine fishes. Brown trout (Salmo trutta) in Europe reportedly become parasitized by ingesting lampreys (Lampetra planeri) carrying infective larvae. However, our field and laboratory observations suggested that North American specimens of T. truttae have an alternative life cycle. High abundances and potential impact of T. truttae in rainbow trout, Oncorhynchus mykiss, in the Colorado River drainage in Grand Canyon, where there are no lampreys, prompted a study on the transmission dynamics of this nematode. Eggs of T. truttae, collected from live gravid females, were incubated in the laboratory. Snails, Physa gyrina and Lymnaea sp., were exposed to T. truttae larvae 3-4 wk later. Active larvae of T. truttae were observed penetrating the intestinal wall of exposed snails, and worm larvae were found in the visceral tissues when examined 1 wk after exposure. Larvae in snails showed little growth and development 2 wk later and corresponded to L3 larvae. Infected snails were fed to hatchery-reared juvenile rainbow trout. Developing stages were subsequently found in the mucosal lining and lumen of trout intestines. Adult male and female (gravid) worms were found in the ceca of trout examined 5-6 mo after consuming infected snails. Larvae found in pepsin/trypsin digests and mucosal scrapings from wild, naturally infected, trout corroborate laboratory findings. Screening of Physa sp. and gammarids collected from Colorado River, Grand Canyon, for natural infections with T. truttae using the ITS1 rDNA marker gave positive results. Truttaedacnitis truttae is the second species, after Truttaedacnitis clitellarius of lake sturgeon, capable of using a snail first intermediate/paratenic host and is similar to several other cucullanids in having a histotropic phase of development in the definitive fish host.

A New Species of Synbranchiella (Cestoda: Proteocephalidae) from the Mountain Mullet ( Dajaus monticola) in Costa Rica.

A new species of the recently erected genus of proteocephalid cestodes, Synbranchiella Arredondo, Alves and Gil de Pertierra, 2017 , is described based on specimens found in the mountain mullet, Dajaus monticola (Bancroft, 1834), from Costa Rica. The new species is placed in Synbranchiella because of the cortical position of the genital organs (typical of the former subfamily Monticelliinae); a robust scolex (lacking a metascolex) having a dome-shaped apex and biloculate suckers (lacking free posterior margins); vitelline follicles in 2 narrow lateral bands; a vagina always anterior to the cirrus-sac; and a genital pore that is markedly pre-equatorial, i.e., close to the anterior margin of proglottids. The new species, Synbranchiella megacirrus, differs from the type and only other species of the genus, Synbranchiella mabelae Arredondo, Alves and Gil de Pertierra, 2017 , that infects the marbled swamp eel, Synbranchus marmoratus Bloch, 1795, in Argentina by the absence of preporal vitelline follicles (present in S. mabelae); a well-developed, large, elongate vaginal sphincter (small and ring-like in S. mabelae); and a large cirrus-sac relative to the proglottid size (cirrus-sac length is on average 48% of the proglottid width in S. megacirrus vs. 31% in the latter species). This is the first adult tapeworm reported from mountain mullet and the first record of the genus outside of South America, thereby greatly extending the range of distribution of species of Synbranchiella.

Phylogenetic Relationships of Spiruromorph Nematodes (Spirurina: Spiruromorpha) In North American Freshwater Fishes.

Nematodes are common in the parasite communities of North American freshwater fishes, and the majority of them belong to 1 conventional order, Spirurida Chitwood, 1933. Within the Spirurida, the superfamilies Habronematoidea Chitwood and Wehr, 1932 and Thelazioidea Sobolev, 1949 have undergone considerable diversification. The dominant families of these 2 superfamilies, Cystidicolidae Skrjabin 1946 and Rhabdochonidae Railliet, 1916, respectively, are particularly common, widely distributed, and diverse, especially in North America, yet their phylogenetic relationships remain largely unexplored. In this study, we use near complete sequences of the 18S rRNA genes ( SSU rDNA) from species in 6 genera ( Capillospirura Skrjabin, 1924, Cystidicola Fischer, 1798, Salmonema Moravec, Santos and Brasil-Sato, 2008, Rhabdochona Railliet, 1916, Spinitectus Fourment, 1883, and a putative new cystidicolid in mooneyes, Hiodontidae), along with a species of Hedruris Nitzsch, 1812 from newts as a surrogate for the fish parasite Hedruris tiara VanCleave and Mueller, 1932, to explore their phylogenetic relationships. These sequences, together with available sequences from a range of other nematodes, including fish nematodes in other groups (Camallanoidea and 'Seuratoidea'), were analyzed using Bayesian inference and maximum likelihood. The results from both analyses indicate, for the first time, support for the close relationships of the sturgeon parasite Capillospirura with Ascarophis van Beneden, 1871 and Cystidicola; the relationship of the cystidicolid from Hiodontidae with Salmonema of salmonid fishes; the monophyly of the 2 dominant spiruridan genera of fishes, Rhabdochona and Spinitectus; and for previous relationships among Nearctic Spinitectus spp. The results also indicate a closer relationship of Rhabdochona and Spinitectus than is suggested by their conventional classification and reject the monophyly of Habronematoidea, Thelazioidea, and Cystidicolidae. Hedruridae appears to be an early branching lineage of spirurins. Finally, the pattern of association between the fish parasites in this study and their hosts indicates, with few exceptions, ecologically driven diversification events involving host shifting not related to the phylogenetic relationships of their hosts.