Taxonomy, systematics, and life cycle of digeneans (Platyhelminthes: Trematoda) infecting freshwater fishes

Abstract

This dissertation is structured in 7 chapters. In the dissertation, I described 4 new digenean species and redescribed 3 species belonging to 7 genera of 5 families, erected 1 new genus, resurrected and emended the diagnoses of 3 genera, and elucidated the life cycle of 3 species, using combined morphological and nucleotide sequence-based (internal transcribed spacer regions [ITS1 and ITS2] and 28S rDNA) evidence. The results of this dissertation are 7 papers that have been published, in press, or under reviewed in peer-reviewed scientific journals, including Journal of Parasitology, Systematic Parasitology, Comparative Parasitology, and Parasitology International. Posthovitellinum psiloterminae n. gen., n. sp. (Lissorchiidae) infects the intestine of Cyclocheilos enoplos (Bleeker, 1849) (Cypriniformes: Cyprinidae), a migratory riverine carp from the Mekong River (Dong Thap province, Vietnam). Posthovitellinum psiloterminae is a unique asymphylodorine by having 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. Pseudoparamacroderoides Gupta and Agrawal, 1968 (Macroderoididae) 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; symmetrical vitelline fields that extend posteriad to the middle of the post-testicular space and that remain separate anteriorly and posteriorly; and an excretory vesicle that is I-shaped and wholly post-ovarian, inter-testicular, or median to the posterior testis. Pseudoparamacroderoides dongthapensis n. sp. infects the intestine of a riverine catfish, Mystus mysticetus Roberts, (Siluriformes: Bagridae) in the Mekong River, Vietnam and differs from its congeners by having an elongate hindbody and an excretory vesicle that is approximately half as long as the body and that extends anteriad beyond the anterior testis. Plesiocreadium Winfield, 1929 (Macroderoididae) differs 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. Plesiocreadium typicum Winfield, 1929 infects 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). Plagioporus wataugaensis n. sp. (Opecoelidae) infects the intestine of the northern hogsucker, Hypentelium nigricans (Lesueur, 1817), and the white sucker, Catostomus commersonii (Lacepède, 1803), (both Cypriniformes: Catostomidae) in the eastern USA. Plagioporus wataugaensis has vitelline fields that are discontinuous at the level of the ventral sucker and follicles that surround the ceca and that span the midline dorsal to the testes and an excretory vesicle that is wholly post-testicular and short (6–9% of the body length). Proterometra wigglewomble n. sp. (Azygiidae) asexually reproduces in the compact elimia, Elimia showalteri (Lea, 1860) (Cerithioidea: Pleuroceridae) and matures in the esophagus of the blackbanded darter, Percina nigrofasciata (Agassiz, 1854) (Perciformes: Percidae) in Cahaba River, Alabama. Adults of the new species differ from congeners by having a small body and eggs having a wholly fimbriated surface that appears as a cilia-like brush border. Live naturallyshed cercariae of the new species differ from those of its congeners by having a strongly claviform tail stem bearing aspinose mammillae, a single furca, excretory pores that open on the posterior margin of the single furca, and few eggs in the cercarial distome. Naturally-shed cercariae of P. wigglewomble secrete a jelly-like adhesive that coats the surface of the furca and evidently facilitates attachment to the surface of glass, plastic, and snail shell and vigorously wiggle about once attached, as if mimicking the larva of a stream insect so as to lure the blackbanded darter to eat it. Adults of Leuceruthrus stephanocauda (Faust, 1921) Womble and Bullard, 2022 (Azygiidae) infect the stomach of spotted bass, Micropterus punctulatus (Rafinesque, 1819), green sunfish, Lepomis cyanellus Rafinesque, 1819, and longear sunfish, Lepomis megalotis (Rafinesque, 1820) from Chewacla Creek (Tallapoosa River, Alabama) and mottled sculpin, Cottus bairdii Girard, 1850 (juvenile) from Raccoon Creek (Chattooga River, Georgia) and differ from its congeners by having an elongated body and an asymmetrical vitellarium. The cercaria of L. stephanocauda sheds from yellow elimia, Elimia flava (Lea, 1862) (Cerithioidea: Pleuroceridae) in Chewacla Creek and Moores Mill Creek (Tallapoosa River) and Elimia caelatura georgiana (Lea, 1862) in Raccoon Creek. Naturally-shed cercariae of L. stephanocauda are unique by having bilateral, discontinuous fields of black tail stem pigmentation posterior to the withdrawn distome and along the margins of the paired furcae, prominent subtriangular spines on the anterior end of the tail stem anterior and posterior to the distome, and broadly rounded to lanceolate furcae that are longer than wide and that bear numerous marginal and submarginal protuberances. Transversotrema cf. patialense (Transversotrematidae) asexually reproduces in the redrimmed melania, Melanoides tuberculata (Müller, 1774) (Cerithioidea: Thiaridae) and matures beneath the scales of the zebrafish, Danio rerio (Hamilton, 1822) (Cypriniformes: Danionidae) within a spring-fed earthen pond aquaculture system (a private aquaculture facility) in the vicinity of Ruskin, Florida. The adult of T. cf. patialense has a body that is 1.8–2.2× wider than long, a ventral sucker that is 1.2–1.7× wider than the pharynx, and a primarily extra-cecal follicular vitellarium extending anteromediad nearly to the level of the eyespots. Cercariae actively swam once liberated from the crushed snails and had well-defined arm-like processes each bearing an adhesive pad, an elongate tail stem, oar-shaped furcae each marginated with a membranous, pleated fin fold, well-developed male and female genitalia, and lacked vitelline follicles. The redia had a broadly rounded anterior body end and a constricted, diminutive tail process at the posterior body end.