Trematodes infecting fishes and reptiles in North America, South America, and Africa: taxonomy and natural history of Caballerotrematidae, Echinochasmidae, Diplodiscidae, and Cryptogonimidae

Abstract

Parasites comprise both the most species-rich and the most undiscovered and undescribed species to science. Parasite habitat (often hidden within their host), and the scarcity of taxonomic expertise are factors contributing to the lack of knowledge of parasite diversity. The Digenea (Platyhelminthes: Trematoda) is the most speciose group of metazoan parasites. Although there are many exceptions, digeneans generally have a complex three-host life cycle, the first host being a mollusk (asexual reproduction), the second a wide variety of invertebrate and vertebrates (ingested by the final host), and the final “definitive” host being a vertebrate (sexual reproduction). The objective of this thesis was to assess digenean diversity in fishes and reptiles from North America, South America, and Africa. The thesis contains the description of a new genus, three new species, supplemental description of two species, and the elucidation of two life cycles. The digeneans described herein were collected from a diverse group of hosts and environments including: an electric eel (Gymnotidae), a bonytongue fish (Arapaimidae), a southern frog (Leptodactylidae) and a coral snake (Elapidae) from the Amazon River Basin in Colombia; a crocodile (Crocodylidae) and an alligator (Alligatoridae) from Namibia and United States, respectively. Each chapter details the taxonomic identity and phylogenetic position of the collected digeneans. Chapter 1 provides a supplemental description of Caballerotrema annulatum (Diesing, 1850) Ostrowski de Núñez and Sattmann, 2002 (Echinostomatoidea: Caballerotrematidae) infecting the intestine of an electric eel, Electrophorus cf. varii from the Yahuarcaca Lake System in Leticia, Amazonas, Colombia. We provided the first nucleotide information for a species of Caballerotrema Prudhoe, 1960 tethered to a morphologically identified specimen deposited in a lending museum. Chapter 2 propose and describe a new genus and species of Caballerotrematidae: Alobophora sandrae Cajiao-Mora and Bullard, 2024 collected from the intestine of Arapaima gigas sensu lato (Osteoglossiformes: Arapaimidae) from the Amazon River near Leticia, Amazonas, Colombia. We reassigned C. annulatum to the new genus as Alobophora annulata (Diesing, 1850) Cajiao-Mora and Bullard, 2024. We also provided a supplemental description and the first nucleotide information for Caballerotrema brasiliense, the type species of the genus, and a dichotomous key for the family. Chapter 3 provides a supplemental description of the type species of Stephanoprora Odhner, 1902: Stephanoprora ornata Odhner, 1902 (Echinostomatoidea: Echinochasmidae), collected from the intestine of a Nile crocodile, Crocodylus niloticus Laurenti, 1768 (Crocodylidae), from Namibia, with the first nucleotide information for the species. The new morphological and nucleotide information suggested Stephanoprora as monotypic, therefore, we emended Mesorchis, previously synonymized with Stephanoprora, to accommodate 25 species. Chapter 4 describes Catadiscus marielaosornae Cajiao-Mora and Bullard, 2025 (Diplodiscidae) collected from the intestine of a Peters’ thin-toed frog, Leptodactylus petersii (Steindachner, 1864) (Leptodactylidae) from the Yahuarcaca Lake System in Leticia, Amazonas, Colombia. The report is the first to describe a digenean infecting a Peters’ thin-toed frog, and the first to report any parasite infecting any Leptodactylus frog from Colombia. Chapter 5 describes Acanthostomum yahuarcaquense Cajiao-Mora and Bullard, 2025 (Cryptogonimidae) collected from the intestine of an aquatic coral snake, Micrurus surinamensis (Cuvier, 1817) (Elapidae) from the Yahuarcaca Lake System in Leticia, Amazonas, Colombia. We discuss the implications of using unidentifiable sequences (nonugens: no morphological description, no voucher, no photo) deposited in GenBank, and the use of excessively short nucleotide sequences to test phylogenetic relationships. The report is the first to record a parasite infecting a coral snake (Micrurus spp.) in Colombia. Chapter 6 describes identical life cycles of two sympatric and closely related cryptogonimids that were previously regarded as junior subjective synonyms: Proctocaecum diploporum (Stunkard, 1931) Baugh, 1957 and Proctocaecum coronarium (Cobbold, 1861) Brooks, 1980. Both species share the same first intermediate host, the cockscomb hydrobe, Littoridinops monroensis (Frauenfeld, 1863) (Gastropoda: Cochliopidae); are encysted within the scales of seven sympatric saltmarsh fishes (second intermediate host), often found infecting the same scale; and mature in the intestine of the same definitive host, the American alligator, Alligator mississippiensis (Daudin, 1802) (Alligatoridae). This is the first complete and naturally occurring life cycle of a reptile-infecting cryptogonimid, and the first nucleotide information for a species of Proctocaecum. We taxonomically reassess both P. diploporum and P. coronarium and designate a neotype for P. coronarium.