An updated checklist of leeches and oligochaetes (Annelida: Clitellata) that parasitize or prey upon wild North American amphibians and reptiles is presented: A total of 25 species grouped in 6 genera, 5 families, and 2 orders, are registered; these infect a total of 39 species of reptiles and 39 species of amphibians in the region. An illustrated identification key for the families and genera listed is proposed. Finally, a new record is made for Mexico: the leech Placobdella parasitica (Say, 1824) (Glossiphoniidae) parasitizing the Mesoamerican slider Trachemys venusta (Gray, 1856) (Emydidae) in the state of Tamaulipas.

Hedruris has a worldwide distribution, parasitizing lampreys, fishes, frogs, and lizards. In South America, 4 species have been reported on frogs (Hedruris heyeri, Hedruris juninensis, Hedruris moniezi, and Hedruris mucronifer), 3 on fishes (Hedruris basilichtensis, Hedruris orestiae, and Hedruris suttonae), and 1 on turtles (Hedruris dratini). We examined a frog (Pseudis minuta) found dead in the Pescado stream, Argentina, searching for parasites. A Hedruris sp. was found and subsequently subjected to integrative analyses. The 18S rDNA was sequenced, and specimens were examined using electron and optical microscopy. Genetic analysis grouped this nematode with H. dratini. Its morphology was similar to that species but differed in having bifid derid in frogs, compared to a simple deirid in turtles. This difference could result from various causes, such as host-parasite interaction or a teratological feature, or it could indicate high morphological variability. To resolve this, molecular analysis of all described Hedruris species is necessary, in addition to morphological studies. According to the prevalence and intensity of infection reported in the literature, the definitive host of H. dratini is likely the turtle. However, the nematode may use different hosts, or the frog may have ingested an amphipod harboring the parasite's intermediate stage. This is the first Hedruris parasite of frogs to be sequenced and represents, after H. mucronifer, the second report of the genus in anurans from Argentina.

Turtle acanthocephalans in the genus Neoechinorhynchus have complex life cycles and are thought to involve an ostracod intermediate host and a turtle definitive host. For Neoechinorhynchus emydis, an additional snail paratenic host is part of its life cycle. However, how snails become infected and whether other species of Neoechinorhynchus can be found in snails remains unclear. This study was conducted to understand the survival, development, and host use of 4 species of turtle acanthocephalans (Neoechinorhynchus chrysemydis, N. emydis, Neoechinorhynchus emyditoides, and Neoechinorhynchus pseudemydis) in their intermediate, paratenic, and definitive hosts. Using eggs recovered from adult acanthocephalans from naturally infected turtle hosts in Oklahoma, experimental infections were conducted in 2 species of ostracods and 1 species of freshwater snail. Ionomes also were generated for these acanthocephalans and their turtle definitive hosts to better understand resource competition. Upon ingestion by ostracods, eggs of all 4 species of acanthocephalans hatched in both ostracod species. However, no further acanthocephalan development occurred in Cypridopsis sp. ostracods, whereas all 4 acanthocephalan species grew and developed into infective juveniles over 28–32 days in Physocypria sp. ostracods. Of the 4 species of acanthocephalans, N. emydis grew faster early in ostracods and was the only species to survive and establish in snail hosts. This finding was supported by the observation of proboscis remnants in the feces of snails that ingested ostracods infected with N. chrysemydis, N. emyditoides, and N. pseudemydis. In contrast, when snails were exposed to eggs of all 4 acanthocephalan species, eggs were passed in the feces, resulting in no infections. The overall ionomic composition of adult acanthocephalans and their turtle hosts suggested that the hosts and parasites share host resources. However, specific elemental differences indicated that turtle acanthocephalans can accumulate heavy metals at concentrations higher than those in their hosts. Results of this study support previous field observations and hypotheses that (1) Physocypria sp. ostracods serve as intermediate hosts for N. chrysemydis, N. emydis, N. emyditoides, and N. pseudemydis; (2) N. emydis uses snail paratenic hosts, but snails are a non-viable route of transmission to turtles for N. chrysemydis, N. emyditoides, and N. pseudemydis; and (3) as adults, these 4 acanthocephalan species utilize their turtle definitive hosts similarly in terms of ionomic composition. This work challenges the traditional view of the acanthocephalan life cycle and sets the stage for future hypotheses.

The range of hosts a parasite can successfully occupy is partially determined by the niche breadth, that is, the set of environmental conditions necessary to maintain a stable population. Niche breadth is often quantified using host specificity, which encompasses the number of host species a parasite can exploit and the parasite's distribution among its hosts. Parasites with a wider niche breadth can potentially occupy more host species and are often more evenly distributed among hosts than parasites with a narrower niche breadth. However, parasites interact with potential hosts within the context of a geographic locality and the set of environmental characteristics associated with it. The extent to which environmental filters associated with host individuals and the geographic context explain variation in occupancy of parasites, and the extent to which variation in occupancy is associated with host range and specificity, is poorly understood. Using data from small mammals and ectoparasites in Vermont, I used a multiscale, multispecies occupancy model (MSOM) to (1) estimate ectoparasite occupancy at 10 geographic sites and on individual hosts within each site, (2) quantify the variation in occupancy explained by the site and host levels of the model using Bayesian R², and (3) evaluate associations between explained variation and host range of ectoparasites. For ectoparasites collected from at least 4 different host species, I calculated structural specificity to determine the distribution of these parasites across the hosts, and β-specificity to evaluate changes in host use across habitats. Host range was significantly associated with host-level Bayesian R²: generalist parasites had more variation in occupancy explained by host-level covariates than specialist parasites. This result may be explained by differences in structural specificity: many generalists disproportionally occurred on a single-host species, suggesting that host characteristics act as habitat filters for these parasites. There were no significant associations between site-level Bayesian R² and host specificity. However, some generalists demonstrated high β-specificity, suggesting these parasites may “switch” hosts, depending on host availability. These results highlight that the terms specialist and generalist are context dependent and may not accurately describe the niche breadth of parasite taxa. Understanding variation in host specificity as it pertains to potential habitat filters may be important for predicting which parasites can bypass host filters and “jump” to a novel host, which has implications for the surveillance and management of vector-borne diseases.

The Cyathocotylidae Mühling, 1896 is a small but broadly distributed family of digeneans parasitic in a wide range of vertebrate definitive hosts, from fish to mammals. Despite existing taxonomic questions, only a few studies have generated DNA sequence data from cyathocotylids, and only a single publication included sequence data from a cyathocotylid parasitic in snakes. Four genera are known to infect snakes: Gogatea Lutz, 1935, Szidatia Dubois, 1938, Mesostephanoides Dubois, 1951, and Serpentostephanus Sudarikov, 1961. Members of these genera were known from only Asia and Africa. In the present study, we describe 2 new species of Gogatea from snakes in Australia and 1 from Vietnam. The new species from Vietnam described herein is the first member of the genus that lacks a ventral sucker. We used partial sequences of the nuclear large ribosomal subunit (28S) and mitochondrial cytochrome c oxidase subunit I (COI) genes to explore phylogenetic relationships among cyathocotylids and species differentiation. In addition, this is the first report of a cyathocotylid from snakes in Australia, thus posing interesting questions regarding the dispersal and historical biogeography of these parasites. Cyathocotylid genera from snakes have a long, convoluted taxonomic history. The genera Gogatea, Mesostephanoides, and Szidatia were distinguished from each other based on very small morphological differences. Therefore, the validity of Szidatia and Mesostephanoides was often questioned in the literature. Based on the detailed morphological analysis of our freshly collected high-quality specimens and comparison with published information, we synonymize Mesostephanoides and Szidatia with Gogatea.

Hepatozoon sp. stages were detected in histological sections of the muscles of 11 of 25 bobcats (Lynx rufus). Parasites were detected from the myocardium of 11, tongues of 4, and limb muscles of 5 of these animals, which had been hunted in Mississippi in 2017. The intensity of infection was highest in the heart. Only asexual stages (meronts) were detected. Three types of meronts (types 1, 2, and 3) were detected, based on structure and mode of division. Additionally, individual zoites were found in leukocytes in the blood vessels of the myocardium, but the stage was not identified. Based on genomic DNA characterized from paraffin-embedded myocardium sections from 1 bobcat using 18S rRNA gene, the Hepatozoon species from the bobcat was related to but distinct from other Hepatozoon spp. of felids. This is the first description of the development of Hepatozoon in the muscles of bobcats. A new name, Hepatozoon rufi, is proposed for this parasite in bobcats.

Nine species of Hemirhamphiculus Bychowsky and Nagibina, 1969 (Dactylogyridae) were recorded from 6 beloniform fishes during a survey of the monogenoids infecting these fishes in the Gulf of Mexico off Florida from September 2017 through December 2020. Five new species were collected, illustrated, and described: Hemirhamphiculus acarips n. sp., Hemirhamphiculus longiclathra n. sp., and Hemirhamphiculus lucernula n. sp. all from Strongylura notata (Poey) and Hemirhamphiculus bilobatus n. sp. and Hemirhamphiculus litus n. sp. both from Strongylura timucu (Walbaum). Four previously described species were transferred to Hemirhamphiculus: Hemirhamphiculus tylosuri (MacCallum, 1917) n. comb. [formerly Ancyrocephalus tylosuri (MacCallum, 1917) Johnston and Tiegs, 1922]; Hemirhamphiculus parvus (Linton, 1940) n. comb. (formerly Ancyrocephalus parvus Linton, 1940); Hemirhamphiculus cornutus (Williams and Rogers, 1972) n. comb. (formerly Ancyrocephalus cornutus Williams and Rogers, 1972); and Hemirhamphiculus trullae (Williams, 1980) n. comb. (formerly Ancyrocephalus trullae Williams, 1980). The occurrence of He. trullae on Hyporhamphus meeki represents a new host record for the parasite. Three Indo-Pacific species of Dactylogyridae were transferred to Hemirhamphiculus: Pseudohaliotrematoides recurvatus Yamaguti, 1968, as Hemirhamphiculus recurvatus (Yamaguti, 1968) n. comb.; Tylosuricola haikouensis Zhang, 2001, as Hemirhamphiculus haikouensis (Zhang, 2001) n. comb.; and Xenentocleidus xenentodoni (Jain, 1961) Tripathi, Agrawal, and Pandey, 2007, as Hemirhamphiculus xenentodoni (Jain, 1959) n. comb. Xenentocleidus Tripathi, Agrawal, and Pandey, 2007, was synonymized with Hemirhamphiculus as its junior subjective synonym. Bychowskymonogenea Caballero and Bravo Hollis, 1972, and Bychowskymonogenea sogandaresi Caballero and Bravo Hollis, 1972, were placed as junior subjective synonyms of Hemirhamphiculus and He. tylosuri, respectively, and the Bychowskymonogeninae Caballero and Bravo Hollis, 1972, was rejected as a valid subfamily of the Dactylogyridae.

Cospeciation has been observed multiple times between parasites and their hosts. Here we compare the phylogeny of 2 different groups of chewing lice (Phthiraptera), one known for being host specific (Amblycera: Myrsidea) and one known for including many generalist species (Ischnocera: Brueelia-complex, specifically Guimaraesiella and Priceiella) with that of their songbird hosts (Passeriformes), which are participants in mixed-species feeding flocks in South China. Using event- (Jane) and distance-based (ParaFit) analyses we found that both groups of lice have phylogenies that are more similar than by chance to those of their hosts. However, more cospeciation and host-switching events were inferred for the Myrsidea data set, whereas more duplication events and losses were inferred for the Brueelia-complex data set. Even though these louse groups are found on roughly the same host species, the differences in sorting events may be linked to the different modes of dispersal. Whereas both groups transfer by direct contact, phoresy is recorded only in lice belonging to the Brueelia-complex.

During August 2021 and again in July 2022 and July 2023, 4 freckled madtoms, Noturus nocturnus, were collected from a creek in Columbia County, Arkansas (Ouachita River drainage), and their gills, gallbladder, fins, integument, musculature, and other major organs were examined for myxozoans. The gallbladder of 1 (25%) was infected with apparently novel myxozoans. Qualitative and quantitative morphological data were from preserved formalin-fixed myxospores. Molecular data include 2,059 bp (for a Myxidium sp.) and 951 bp (for an unobserved Myxozoa sp.) sequences of the partial small subunit (SSU) ribosomal RNA gene. Phylogenetic analysis placed the Myxidium sp. among a clade of myxozoans that infect fish from the southern portion of North America. These represent the first myxozoans reported from the gallbladder of madtoms.