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In this study, the structure of metazoan endoparasites infracommunities and component community in Erythrolamprus poecilogyrus caesius (Cope, 1862) (Serpentes: Dipsadidae) is presented. From 21 specimens (15 females; 6 males) collected between February 2017 and March 2022 at Ingeniero Juárez, Formosa, Argentina, 90.5% of individuals surveyed (n= 19) were infected with at least one species of metazoan endoparasite. Nine hundred sixty specimens were collected (117 adults; 843 larvae), from 11 taxa. Kalicephalus appendiculatus (Nematoda), Raillietiella furcocerca (Pentastomida), Ophiotaenia joanae, Catadiscus uruguayensis, Opisthogonimus lecithonotus (Platyhelminthes) were found as adults. Larvae identified were Oligacanthorhynchus sp. (Acanthocephala), Physaloptera sp. (Nematoda), Strigea spp. and Alaria sp. (Digenea). Digenea was the richest group (S= 6). Adults were collected in intestines, trachea and esophagus, while larvae were found in mesenteries and body cavity. Ophiotaenia joanae was the most prevalent species (38.1%) and K. appendiculatus had the highest mean abundance (3.7). Considering larvae, Strigea spp. were dominant and Oligacanthorhynchus sp. was subdominant. Between pairs of metazoans, positive and negative covariations were obtained. In general, intensity of metazoan taxa had positive correlation to host weight and body condition but had negative relationships with snout-vent length. Mean infracommunity richness (including larvae and adults) was 4.35 ± 1.27 taxa/host. Richness and diversity were higher in larval infracommunities than those composed by adults. This is the first ecological study of endoparasites in snakes from Argentina. New reports to parasite biodiversity in Dry Chaco were added, also, information about habitat use, diet, and position in trophic webs of host was generated.

Purpose Cosmocercids are common nematodes that parasitize the digestive tract and lungs of amphibians and reptiles around the world. They are commonly found in leptodactylid and bufonid anurans in South America, primarily in Brazil and Argentina. This paper describes a new species of genus Cosmocerca based on specimens collected in a microhylid from the Dry Chaco ecoregion. Methods A total of 18 specimens of Elachistocleis haroi were collected in October 2011 in Chaco province and in December 2021 and March 2022 in Formosa province, Argentina, both areas of the Dry Chaco ecoregion. The morphology of the nematodes was studied in detail using light microscopy and scanning electron microscopy. Results One hundred and fifty-one nematodes were collected from the large intestines of E. haroi. Based on the morphology of the caudal papillae (rosette papillae and plectanes), the presence of two spicules and the absence of caudal alae in males, and the presence of two prodelphic ovaries in females, these specimens were allocated to the genus Cosmocerca . However, they presented unique characteristics that differentiate them from all known species. Cosmocerca wichiorum sp. nov. is similar to C. archeyi , C. australis , C. sardiniae , C. zugi , and C. leytensis by having four pairs of plectanes, but can be easily distinguished from all of them by the type, number, and arrangement of the precloacal (non-plectanes), adcloacal and postcloacal papillae, by the length of the spicules and by its different zoogeographical distribution. Conclusion This is the 14th species of the genus Cosmocerca described in South America and the first one for the microhylid E. haroi from the Dry Chaco ecoregion.

This article presents a checklist of metazoan parasites of snakes from Argentina, along with a comprehensive review of the relevant literature published between 1922 and June 2023, covering various aspects of interest. We compiled 34 species of metazoan endoparasites from 28 studies. The subclass Digenea showed the highest number of species (n = 22 species), followed by the phylum Nematoda (n = 8 species), and the subclass Pentastomida (n = 3 species and 1 taxa inquirenda). Dipsadidae was the family of snakes with the most species examined for metazoan endoparasites (n = 20 species). In contrast, Viperidae had the largest number of specimens surveyed (n = 343). Of 23 provinces, 15 (65.2%) presented at least one report of metazoan endoparasites in snakes. The northeastern provinces showed the highest richness of metazoan endoparasites and host diversity. Many articles focused on taxonomy, but studies on parasite ecology were not found. Although taxonomic accuracy was high in most reports, some records were correctly deposited in zoological collections or geo-referenced. This is the first attempt to include all groups of metazoan endoparasites of snakes from Argentina in a single checklist in the last century.

This is the first review of the nematode parasites of amphibians from Dry Chaco (DC) and Humid Chaco (HC) ecoregions of South America, covering aspects related to their systematics, distribution, host range and ecology, including their life cycles. Of approximately 100 species of amphibians that inhabit these ecoregions, the nematode parasites of 32 species are known. The parasite species consisted of 51 taxa: 27 in HC and 18 in DC. The family Cosmocercidae alone included 18 species. Aplectana hylambatis and Cosmocerca podicipinus showed the widest geographical and host distribution. Leptodactylus bufonius and Rhinella major presented a high number of nematode parasites. The species richness of nematodes was related to the host body sizes and to the strategy to obtain prey. The mean species richness was higher in terrestrial amphibians with intermediate characteristics in the generalist–specialist spectrum in terms of diet, and in amphibians with intermediate characteristics between actively foraging and the “sit-and-wait” approach in terms of searching for prey. The patterns of similarity among amphibian species showed groups linking with their habitats. Nematodes usually have direct life cycles with the infectious form entering the host passively or actively. However, many amphibians are also involved in heteroxenous cycles that develop in the aquatic environment.

Cruzia Travassos, 1917 is a diverse genus of nematode parasites in amphibians, reptiles, and mammals. During a parasitological survey, specimens of Cruzia were found in the intestine of the lizards Ameiva ameiva (Linnaeus) and Teius teyou (Daudin) (Squamata: Teiidae) at the Chaco region, Formosa province, Argentina. A comparative analysis revealed that these nematodes represent a new species, named as Cruzia toba n. sp. The new species can be distinguished from the congeners based on the combination of the following features: presence 12–14 teeth per row in the pharynx, equatorial vulva in females, and number and arrangement of caudal papillae in males (11 pairs: 3 precloacal, 3 paracloacal, 5 postcloacal; plus a precloacal minute unpaired papilla). Cruzia toba n. sp. is closely related to C. lauroi Vieira, Gonçalves, Lima, Sousa, and Muniz-Pereira, 2020 a likewise parasite of lizards, regarding the length of spicules and the presence of an unpaired papilla in males, but differs from it in the position of the vulva, the size of the gubernaculum and in the number and arrangement of caudal papillae. This is the first report of a representative of Kathlaniidae parasitizing A. ameiva and T. teyou , and the first Cruzia infecting lizards from Argentina. The morphological affinities among species of Cruzia are mostly random, not allowing a morphological grouping of these parasites in relation to their host taxa, or geographic origin. Thus, the speciation process in Cruzia most likely occurred via host capture.

The present study describes the diversity of helminth parasites of Rhinella major (Anura: Bufonidae) in relation to their body size in 4 subhumid vs. semiarid sampling sites from the Argentine Chaco region. Helminths were found in 81% of the specimens examined (n = 85). Fifteen species (13 in subhumid and 7 in semiarid areas) of helminth parasites were found, and most of them were nematodes. Parasites were found in all the examined organs, with highest prevalence and intensity in the digestive tract. Parasite transmission to the toad host occurs by skin penetration or oral ingestion. Maximum helminth richness ranged between 2 and 4 species per infected toad. The most abundant species was Aplectana hylambatis. Body size of the host was the main factor in determining parasite richness. The helminth parasite fauna was rather different in hosts from subhumid vs. semiarid sites, but the dominant (Aplectana hylambatis) and codominant species (Cylindrotaenia sp. and Rhabdias elegans) were the same. Mean species richness and mean species diversity of helminths were significantly different between the zones. These results suggest that the amount of rainfall and associated humidity affects the distribution and development of the parasite fauna of this toad.

This is the first record of the nematode parasite Schulzia travassosi (Trichostrongylina, Molineidae) in two Argentinean amphibians, Leptodactylus bufonius and Rhinella major , collected in two localities of the Chaco region, Las Lomitas (Formosa Province) and Taco Pozo (Chaco Province). The species was observed using light and scanning electron microscopy (SEM) and compared with previous studies of Paraguayan specimens. Regarding metric characters, the measurements found in Argentinean specimens generally did not differ from those of Paraguayan specimens; some differences were observed in the total length of males and females (some longer and some shorter than Paraguayan specimens), length of the oesophagus (in almost all specimens shorter than in Paraguayan ones) and position of the vulva (nearer to posterior end in Argentinean specimens). The branches and sphincter of ovejector are slightly longer than in Paraguayan female specimens. In males, ray 4 is almost the same length as rays 2, 3 and 5, 6. Cephalic end, cephalic vesicle, synlophe and vulvar depression were viewed under SEM. Schulzia melanostictusi Chopra, Shing and Kumar, 1986 is reassigned as Oswaldocruzia melanostictusi (Chopra, Shing and Kumar, 1986) nov. comb.

A total of 36 adult individuals of Leptodactylus latinasus were collected near the city of Corrientes, Province of Corrientes in Argentina. The main goals of this study were: (1) to determine the helminth parasite fauna of L. latinasus; (2) to determine the richness and diversity of parasites at the component and infracommunity levels; (3) to analyze the relationships between helminth, frog body size and sex, and (4) to identify and examine species affinity of helminth communities. The helminth component community of this frog’s population consisted of 17 species. The predominant groups of parasites were the trematodes (adults: Glypthelmins repandum, Catadiscus inopinatus and Haematoloechus longiplexus; larvae: Travtrema aff. stenocotyle, Bursotrema aff. tetracotyloides, Styphlodora sp., unknown opisthogonimid species, Petasiger sp. and unknown strigeid species), followed by the nematodes (Cosmocerca podicipinus, C. parva, C. rara, C. cruzi, Schrankiana schranki and Aplectana hylambatis); other groups of parasites were represented by only one species (unknown larval cestode species and Centrorhynchus sp.). All parasite helminth species showed an aggregated pattern of distribution. The most infected organs were kidneys, small intestine, large intestine and pharyngeal zone. The host body size was important in determining the parasites abundance of G. repandum. At the level of component community G. repandum was the species with highest prevalence of infection and Bursotrema aff. tetracotyloides was the dominant species. Helminth species showed four significant pairs of covariation and two significant pairs of association in the infracommunities of Leptodactylus latinasus.

Here, we describe a new kathlaniid nematode, Falcaustra sanjuanensis sp. nov., from the large intestine of Odontophrynus cf. barrioi (Anura: Cycloramphidae), from San Juan Province, Argentina. The new species belongs to the Falcaustra group that possesses a pseudosucker. It resembles F. andrias in the distribution pattern of caudal papillae (six precloacal, four adcloacal, 12 postcloacal, one unpaired median anterior to the cloaca) but differs from F. andrias in the following characters: the longer size of males and females (11.17–13.45 mm and 10.1–15.5 mm, respectively); the longer size and form of the gubernaculum (0.17–0.23 mm, triangular form); the arrangement of postcloacal papillae (three pairs on the ventral side, two pairs on the lateral side, one pair on the subventral side) and unpaired papilla anterior to the cloaca located on the protuberance. The species description is based on light microscopy and scanning electron microscopy (SEM). Falcaustra sanjuanensis sp. nov. represents the 12th Neotropical species assigned to the genus. Also, we added a key to Neotropical species of Falcaustra .

Neocosmocercella fisherae n. sp. is the first nematode species found parasitising Phyllomedusa bicolor from the Brazilian Amazon Region. The new species has a triangular oral opening, with bi-lobed lips, and is distinguished from N. bakeri (triangular oral opening with simple lips), and from N. paraguayensis (hexagonal oral opening with bi-lobed lips). Additionally, the new species has ciliated cephalic papillae, which are absent in the other species of the genus. The reduced uterine sac and the presence of a single egg in the uterus in females are the main morphological characters that differentiate the new species from its congeners N. bakeri (8–10 eggs) and N. paraguayensis (10 eggs, based on the allotype). Additionally, the new species differs from the other two species of the genus by morphometric characters such as the size of spicules and gubernaculum in males and the vagina in females. Until now, phyllomedusid anurans are the only known hosts for the nematodes of this genus. The present work describes the third species of the genus and the first species of nematode parasitising P. bicolor.