A New Species of ThelohanellusKudo, 1933 (Myxozoa: Bivalvulida) Infecting Skeletal Muscle of Blacktail Shiner, Cyprinella venusta Girard, 1856 (Cypriniformes: Cyprinidae) in the Chattahoochee River Basin, Georgia

A NEW SPECIES OF THELOHANELLUS (CNIDARIA: MYXOSPOREA: MYXOBOLIDAE) FROM THE GILL OF QUILLBACK, CARPIODES CYPRINUS (CYPRINIFORMES: CATOSTOMIDAE), FROM THE ARKANSAS RIVER DRAINAGE OF OKLAHOMA

During May 2022 and again in March 2023, 5 quillbacks, Carpiodes cyprinus, were collected from the Verdigris River, Wagoner County, Oklahoma (n = 1), and the Black River, Lawrence County, Arkansas (n = 4), and their gill, gallbladder, fins, integument, musculature, and other major organs were macroscopically examined for myxozoans. Gill lamellae from the single quillback from the Verdigris River was infected with a new myxozoan, Thelohanellus oklahomaensis n. sp. Qualitative and quantitative morphological data were obtained from fresh and formalin-fixed preserved myxospores, and molecular data consisted of a 1,767 base pair sequence of the partial small subunit (SSU) ribosomal RNA gene. Phylogenetic analysis grouped T. oklahomaensis n. sp. with myxozoans known to infect North American catostomids and Eurasian cyprinids. Histological examination localized plasmodia to an intralamellar developmental site and revealed a possible vestige of a second polar capsule. Although plasmodia markedly expanded lamellae, there were no associated epithelial or inflammatory changes. Thelohanellus oklahomaensis n. sp. is the only member of the genus known to infect the gills of C. cyprinus.

A new species of Ellipsomyxa Køie, 2003 (Bivalvulida) infecting the gall bladder of Pangasius macronema Bleeker (Siluriformes: Pangasiidae) from the Mekong River Delta, Vietnam

During a parasitological survey of freshwater fishes in the Mekong River Delta, Vietnam, disporic plasmodia containing myxospores morphologically consistent with Ellipsomyxa Køie, 2003 (Bivalvulida) were observed infecting the gall bladder of Pangasius macronema Bleeker (Siluriformes: Pangasiidae). Herein, we use morphology and small subunit ribosomal DNA (SSU rDNA, 18S) sequence data to describe Ellipsomyxa intravesica Ksepka & Bullard n. sp. and relate it to other myxozoans. The new species resembles Ellipsomyxa adlardi Whipps & Font, 2013, which infects the naked goby, Gobiosoma bosc (Lacepede) (Gobiiformes: Gobiidae) in Lake Pontchartrain, Louisiana, but differs from it by having a longer myxospore (mean = 13.3; range = 12.0-15.0 vs. 12.4; 11.3-14.4) and shorter polar capsules (3.7; 3.0-4.0 vs. 4.3; 3.9-4.9). The 18S phylogenetic analysis recovered the sequence of the new species sister to those ascribed to Ellipsomyxa ariusi Chandran, Zacharia, Sathianandan & Sanil, 2020 and Ellipsomyxa sp. (MK561979); both of which infect the gall bladder of the threadfin sea catfish, Arius arius (Hamilton) (Siluriformes: Ariidiae) from the southwest coast of India. Consistent with previous phylogenetic analyses of Ellipsomyxa spp., Ellipsomyxa was recovered as monophyletic. The new species is the first species of Ellipsomyxa reported from a freshwater fish in Asia and the first myxozoan reported from P. macronema.

A NEW SPECIES OF HENNEGUYA THÉLOHAN, 1892 (CNIDARIA: BIVALVULIDA: MYXOBOLIDAE) INFECTING THE SUBMUCOSA OF THE INTESTINE AND PYLORIC CECA OF RED DRUM, SCIAENOPS OCELLATUS (LINNAEUS) (PERCIFORMES: SCIAENIDAE) FROM COASTAL ALABAMA

A new species of Henneguya Thélohan, 1892 (Bivalvulida: Myxobolidae) is described from the submucosa of the intestine and pyloric ceca of red drum (Sciaenops ocellatus [Linnaeus, 1766] [Perciformes: Sciaenidae]) from the Gulf of Mexico off Gulf Shores, Alabama. Henneguya albomaculata n. sp. differs from all congeners by the combination of myxospore dimensions, polar tubule coil count, the presence of an iodinophilic vacuole in the sporoplasm, and small-subunit ribosomal deoxyribonucleic acid (SSU rDNA) sequence. A phylogenetic analysis of the SSU rDNA recovered H. albomaculata sister to Henneguya cynosioniDykova, de Buron, Roumillat, and Fiala, 2011 in a clade composed of 11 species of Henneguya and 1 species of Myxobolus Bütschli, 1882 (Bivalvulida: Myxobolidae) that collectively infect fishes in marine or estuarine systems. Histologic sections of infected intestine and pyloric ceca revealed plasmodia of H. albomaculata n. sp. developing in the loose connective tissue of the submucosa. The new species comprises the second species of Henneguya reported from red drum.

A new Myxobolus (Cnidaria: Myxosporea: Myxobolidae) from the gills of the southern striped shiner, Luxilus chrysocephalus isolepis (Cypriniformes: Leuciscidae), from southwestern Arkansas, USA

The southern striped shiner, Luxilus chrysocephalus isolepis (Hubbs & Brown) is a relatively large minnow belonging to the true minnow family Leuciscidae Bonaparte. Between May 2020 and January 2022, 55 L. c. isolepis were collected from watersheds in Montgomery (n = 6), Polk (n = 17) and Sevier (n = 32) counties, Arkansas, USA, and their gills, gallbladders, urinary bladders, fins, integument, other major organs, and musculature were examined for myxozoans. Gills of 11 (34%) individual southern striped shiners from Sevier County were infected with a new myxozoan, Myxobolus carlhubbsi n. sp. A qualitative and quantitative morphological description was based on formalin-fixed preserved myxospores, and molecular data consisted of a 1,970 base pair sequence of the partial small subunit rRNA gene from ethanol-preserved specimens. Histologically, plasmodia filled and expanded interlamellar troughs. Hyperplastic epithelial and goblet cells filled interlamellar troughs adjacent to plasmodia, but inflammatory response was limited to scattered lymphocytes. Phylogenetic analysis revealed that M. carlhubbsi n. sp. is a member of a clade of species with pyriform myxospores parasitizing North American Pogonichthyinae Girard and North American and Eurasian Leuciscinae Bonaparte. This is the first report of a myxozoan from L. c. isolepis. This article was registered in the Official Register of Zoological Nomenclature (ZooBank) as urn:lsid:zoobank.org:pub:D10D71C2-2C75-4A1C-80ED-B98FF36CB509.

A NEW SPECIES OF MYXOBOLUS (CNIDARIA: MYXOSPOREA: MYXOBOLIDAE) FROM THE GILLS OF CREEK CHUB, SEMOTILUS ATROMACULATUS (CYPRINIFORMES: LEUCISCIDAE: PLAGIOPTERINAE), FROM THE OUACHITA DRAINAGE OF ARKANSAS

During October and November 2021, 33 creek chubs, Semotilus atromaculatus, were collected from 3 sites in Polk County, Arkansas (Ouachita River drainage), and their gills, gallbladder, fins, integument, musculature, and other major organs were examined for myxozoans. The gills of 9 (27%) were infected with a new myxozoan, Myxobolus fountainae n. sp. Qualitative and quantitative morphological data were from fresh and formalin-fixed preserved spores, while molecular data consisted of a 1918 base pair sequence of the partial small subunit ribosomal RNA gene. Phylogenetic analysis grouped M. fountainae n. sp. with the other leuciscid-infecting myxobolids from North America and within a larger clade of European myxozoans. In addition, histological information is provided on the infection. A previous record of Myxobolus muelleriBütschli, 1882, from the gills and ureters of S. atromaculatus is considered invalid and represents an unknown species. Myxobolus fountainae n. sp. is the only named myxozoan known to infect the gill filaments of S. atromaculatus, whereas Myxobolus pendula (Guilford, 1967) infects the gill arches.

Morphological and molecular studies on two myxosporean infections of cyprinid fishes: Thelohanellus pyriformis from tench and Thelohanellus cf. fuhrmanni from nase

During surveys on myxosporean parasites of Lake Balaton and River Danube fishes, two Thelohanellus spp. were found on tench (Tinca tinca) and on common nase (Chondrostoma nasus). They were identified as Thelohanellus pyriformis and Thelohanellus cf. fuhrmanni, respectively. Myxospores of T. pyriformis from tench were collected from arteria branchialis afferens of gill filaments. The mature myxospores of this species were pyriform in shape and 19 ± 0.6l (18–19.5) long, 8.2 ± 0.54 (7.5–9) wide, 7.3 ± 0.25 (7–7.5) thick containing polar tubules with 9–10 turns. The plasmodia of Thelohanellus cf. fuhrmanni were collected from under the skin of snout of the common nase. The myxospores were pyriform, 16.3 ± 0.39l (15.5–16.5) long, 6.5 ± 0.55 (6.3–7) wide, 6.3 ± 0.53 (5.8–7) thick containing polar tubules with 6 turns. Small subunit ribosomal DNA sequences of both Thelohanellus species differed from other known myxozoans. The myxospores morphology, histopathology and ssrDNA sequences supported a diagnosis of T. pyriformis from tench and T. cf. fuhrmanni from common nase.

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Two Thelohanellus spp. were redescribed from cyprinid fishes.

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Thelohanellus pyriformis was recorded and described from the type host tench (Tinca tinca).

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Thelohanellus cf. fuhrmanni was found in an atypical host, common nase (Chondrostoma nasus).

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The morphology of both Thelohanellus species was supported by histology and ssrDNA sequence data.

Two new species of Myxobolus (Myxozoa: Myxobolidae) infecting the gill and scales of the smallmouth bass, Micropterus dolomieu (Centrarchiformes: Centrarchidae) in the French Broad River Basin, North Carolina

Two new species of Myxobolus Bütschli, 1882 (Bivalvulida: Myxobolidae) are described from the gill and scales of smallmouth bass (Micropterus dolomieu Lacepède, 1802 [Centrarchiformes: Centrarchidae]) from the Watauga River, French Broad River Basin, North Carolina, United States. Myxobolus intralamina n. sp. infects the lumen of the lamellar arterioles and Myxobolus infrabractea n. sp. infects the inner surface of the scale. They differ from all congeners by a combination of myxospore dimensions, polar tubule coil count, and the presence or absence of an iodinophilic vacuole in the sporoplasm and an intercapsular process. A phylogenetic analysis of the small subunit ribosomal DNA (SSU rDNA) recovered M. intralamina n. sp. sister to Myxobolus lepomis and Myxobolus branchiarum and M. infrabractea n. sp. sister to Myxobolus micropterii in a clade composed of five Myxobolus spp. infecting centrarchids and Henneguya spp. (Myxobolidae) infecting percids. Histological sections of infected gill revealed intra-lamellar plasmodia of M. intralamina n. sp. within the lumen of the lamellar arterioles and plasmodia of M. infrabractea n. sp. developing beneath the scales. These new species comprise the first species of Myxobolus reported from a black bass (Micropterus Lacepède, 1802) in the Southeast United States.

New data on Henneguya postexilis Minchew, 1977, a parasite of channel catfish Ictalurus punctatus, with notes on resolution of molecular markers for myxozoan phylogeny

Previous morphological and histological data are supplemented with molecular and ultrastructural data for a Henneguya sp. isolated from farm-raised channel catfish Ictalurus punctatus in Mississippi, USA. Myxospores were cryptic, encapsulated within a thin layer of epithelium in the gill lamellae with spore measurements consistent with the original description of Henneguya postexilis Minchew, 1977. Myxospores were 42.7-49.1 µm in total length with spore bodies 12.1-17.2 × 3.6-4.8 × 2.9-3 µm. Polar capsules were of unequal length, with the longer capsule being 4.4-6.7 × 1.1-1.6 µm and the shorter capsule being 4.4-6.4 × 1.1-1.6 µm. Polar tubules had 6-8 turns. Caudal processes were 25.7-38.1 µm in length. Spores were encapsulated in a thin layer of epithelium in the gill lamellae. Molecular data from the most commonly used markers for myxozoan identification and phylogeny, partial 18S small subunit ribosomal gene (SSU), partial 28S large subunit ribosomal gene (LSU), and elongation factor 2 (EF2) were generated for H. postexilis. Additionally, novel data for LSU and EF2 were generated for archived myxozoan specimens from farm-raised catfish (H. mississippiensis, H. ictaluri, H. exilis, H. adiposa, H. sutherlandi, H. bulbosus, Unicauda fimbrethilae), as well as archived specimens from wild fish (H. laseeae [from Pylodictis olivaris], Hennegoides flockae [from Aphredoderus sayanus], Myxobolus cloutmani [from Cycleptus elongatus]. These include the first EF2 sequence data for the genera Hennegoides and Unicauda. Phylogenetic analyses using these data placed H. postexilis in well supported clades with other ictalurid-infecting Henneguya species. Phylogenetic signal assessments on these analyses suggest that while SSU provided the greatest phylogenetic signal, LSU yielded comparable signal, supporting previous work implying this region may be underutilised in reconstructing myxobolid phylogenies.

Two new species of Myxobolus Bütschli, 1882 (Cnidaria: Bivalvulida: Myxobolidae) infecting the gill of the black redhorse, Moxostoma duquesnei (Lesueur) (Cypriniformes: Catostomidae) in the Little Tennessee River Basin, North Carolina

Two new species of Myxobolus Bütschli, 1882 (Bivalvulida: Myxobolidae) are described from the gill of the black redhorse (Moxostoma duquesnei [Leueur][Cypriniformes: Catostomidae]) from the Little Tennessee River Basin, North Carolina, United States. Myxobolus branchiofilum n. sp. infects lumen of the lamellar arterioles and Myxobolus branchiopecten n. sp. infects the bone and cartilage at the tip of the gill rakers. They differ from all congeners by a combination of myxospore dimensions and the presence or absence of an iodinophilic vacuole in the sporoplasm, mucous envelope, intercapsular process, and sutural markings. A phylogenetic analysis of the small subunit ribosomal DNA recovered M. branchiopectin sister to Myxobolus sp. (AF378343) in a clade composed of 6 species of Myxobolus, which infect predominately cypriniform intermediate hosts. Myxobolus branchiofilum was recovered sister to Myxobolus ictiobus Rosser, Griffin, Quiniou, Alberson, Woodyard, Mischker, Greenway, Wise & Pote, 2016 in a clade composed of 8 species of Myxobolus, which predominately infect catostomid intermediate hosts. Histological sections of infected gill revealed intra-lamellar plasmodia of M. branchiofilum in the lumen of the lamellar arterioles and foci of M. branchiopecten developing in the bone and cartilage of the gill raker tip. These are the first myxozoans reported from the black redhorse. Given that these two new species are morphologically congeneric but recovered in distantly related clades, we discuss the persistent issue of myxobolid genera paraphyly/polyphyly.

A NEW SPECIES OF MYXOBOLUS (CNIDARIA: MYXOSPOREA: MYXOBOLIDAE) FROM THE BLUE SUCKER, CYCLEPTUS ELONGATUS (LESUEUR) (CYPRINIFORMES: CATOSTOMIDAE: CYCLEPTINAE), FROM ARKANSAS

During 9-10 February 2018 and 21-22 February 2020, 7 adult Blue Suckers, Cycleptus elongatus, were collected by hoop nets from the Red River, Little River County (n = 3), and the Black River, Lawrence County (n = 4), Arkansas, and their gills, gallbladders, fins, integument, other major organs, and musculature were examined for myxozoans. All 7 (100%) were infected with an unknown species of gill-infecting Myxobolus sp. Twenty formalin-fixed plasmodia (cysts) of Myxobolus cloutmani n. sp. were elliptoidal, 407 μm long × 270 μm wide. Formalin-fixed myxospores were orbicular to broadly elliptoidal, 8.7 μm long × 7.8 μm wide. Two polar capsules were pyriform and subequal in size, extending over halfway in the myxospore. The larger polar capsule was 5.5 μm long × 3.1 μm wide, while the shorter was 5.1 × 2.9 μm. A coiled polar filament possessed 5 or 6 coils. The myxospore was 3.7 μm thick in sutural view, with a distinct sutural ridge. Qualitative and quantitative morphological data were from formalin-fixed as well as ethanol-preserved spores, while molecular data consisted of a 2,010 base pair sequence of the partial 18S ribosomal RNA gene and a 2,502 base pair sequence of the partial 28S ribosomal RNA gene. Phylogenetic analysis grouped M. cloutmani n. sp. with the other catostomid-infecting myxobolids. This is the first myxozoan reported from C. elongatus.

A new species of Myxobolus Bütschli, 1882 (Bivalvulida: Myxobolidae) infecting stratum spongiosum of the imperiled sicklefin redhorse, Moxostoma sp. (Cypriniformes: Catostomidae) from the Little Tennessee River, North Carolina, USA

The sicklefin redhorse, Moxostoma sp. (Cypriniformes: Catostomidae), is an innominate imperiled catostomid endemic to the Hiwassee and Little Tennessee river basins, which has been restricted to a few tributaries of these systems by impoundments. During collections to propagate sicklefin redhorse for reintroduction, a myxozoan, described herein, was observed infecting sicklefin redhorse in the Little Tennessee River Basin, North Carolina. Myxobolus naylori Ksepka et Bullard sp. n. infects the stratum spongiosum covering the scales of sicklefin redhorse. Myxospores of the new species differ from all congeners by the combination of having a mucous envelope, intercapsular process, and sutural markings as well as lacking an iodinophilic vacuole in the sporoplasm. A phylogenetic analysis of the 18S rDNA gene recovered the new species in a polytomy with Myxobolus marumotoi Li et Sato, 2014 and a clade comprised of species of Myxobolus Bütschli, 1882; Thelohanellus Kudo, 1933, and Dicauda Hoffman et Walker, 1973. Histological sections of infected sicklefin redhorse skin revealed myxospores within a plasmodium in the stratum spongiosum dorsal to scales, encapsulated in collagen fibres, and associated with focal erosion of scales directly beneath the plasmodium; in some instances, the scale was perforated by the plasmodium. The specificity of the new species to sicklefin redhorse may make it a useful biological tag to differentiate sicklefin redhorse from morphologically similar species. The new species is the first parasite reported from sicklefin redhorse, a species of concern to the United States Fish and Wildlife Service. No species of Myxobolus has been reported from species of Moxostoma in the Southeast United States. As it was observed that Myxobolus minutus Rosser, Griffin, Quiniou, Alberson, Woodyard, Mischker, Greenway, Wise et Pote, 2016 is a primary junior homonym of Myxobolus minutus Nemeczek, 1911, we propose the replacement name Myxobolus diminutus (Rosser, Griffin, Quiniou, Alberson, Woodyard, Mischker, Greenway, Wise et Pote, 2016).