The South American subcontinent supports one of the world's most diverse and commercially very important ichthyofauna. In this context, the study of South American fish parasites is of increased relevance in understanding their key roles in ecosystems, regulating the abundance or density of host populations, stabilizing food webs and structuring host communities. It is hard to estimate the number of fish parasites in South America. The number of fish species studied for parasites is still low (less than 10%), although the total number of host-parasite associations (HPAs) found in the present study was 3971. Monogeneans, with 835 species (1123 HPAs, 28.5%), and trematodes, with 662 species (1127 HPAs, 30.9%), are the more diverse groups. Data gathered from the literature are useful to roughly estimate species richness of helminths from South American fish, even though there are some associated problems: the reliability of information depends on accurate species identification; the lack of knowledge about life cycles; the increasing number of discoveries of cryptic species and the geographically biased number of studies. Therefore, the closest true estimations of species diversity and distribution will rely on further studies combining both molecular and morphological approaches with ecological data such as host specificity, geographical distribution and life-cycle data. Research on biodiversity of fish parasites in South America is influenced by problems such as funding, taxonomic impediments and dispersion of research groups. Increasing collaboration, interchange and research networks in the context of globalization will enable a promising future for fish parasitology in South America.

A new genus of dactylogyrid monogeneans (Ancyrocephalinae), Paracosmetocleithrum n. gen., is erected to accommodate P. trachydorasi n. sp. from Trachydoras paraguayensis (Siluriformes: Doradidae) in the Upper Paraná River basin, Brazil. The new genus differs from Neotropical dactylogyrids in the presence of a well-developed ornamentation in the middle portion of the ventral bar, and a sclerotized patch on the surface of the dorsal bar with an inconspicuous medial process that possesses two submedial projections arising from the tapered ends of this patch. In addition, Demidospermus rhinelepisi n. sp. is described from Rhinelepis aspera (Siluriformes: Loricariidae). The new species, which is the fifth species of the genus described from loricariids, can be differentiated from congeners by the possession of a sclerotized patch attached to the middle portion of the ventral bar, and by morphology of the accessory piece, which presents broad ends, tapering in the centre, rounded proximal end, distal end folding on both sides with folds extending to approximately ¾ of the accessory piece length. Molecular data on both new species are also provided and species composition of Demidospermus, recently revealed as polyphyletic by molecular studies including the present one, is discussed.

A checklist of records of aspidogastrean trematodes (Aspidogastrea) is provided on the basis of a comprehensive survey of the literature since 1826, when the first aspidogastrean species was reported, until December 2014. We list 61 species representing 13 genera within 4 families and 2 orders of aspidogastreans associated with 298 species of invertebrate and vertebrate hosts. The majority of records include bivalves (44% of the total number of host-parasite associations), whereas records from bony fishes represent 32% of host-parasite associations. The aspidogastreans have worldwide distribution, with the highest number of records in the Neartic Region for freshwater hosts and the North Atlantic Ocean for marine ones. The checklist includes a parasite-host list with data on host habitat, site of infection and distribution area of parasites, and a host-parasite list. A limited number of molecular studies on aspidogastreans does not allow us to unravel phylogenetic relationships within the Aspidogastrea.

An exhaustive literature search supplemented by a critical examination of records made it possible to present an annotated checklist of tapeworms (Cestoda) that, as adults or larvae (metacestodes), parasitize freshwater, brackish water and marine fishes, i.e. cartilaginous and bony fishes, in South America. The current knowledge of their species diversity, host associations and geographical distribution is reviewed. Taxonomic problems are discussed based on a critical evaluation of the literature and information on DNA sequences of individual taxa is provided to facilitate future taxonomic and phylogenetic studies. As expected, the current knowledge is quite uneven regarding the number of taxa and host-associations reported from the principal river basins and marine ecoregions. These differences may not only reflect the actual cestode richness but may also be due to the research effort that has been devoted to unravelling the diversity of these endoparasitic helminths in individual countries. A total of 297 valid species, 61 taxa identified to the generic level, in addition to unidentified cestodes, were recorded from 401 species of fish hosts. Among the recognized cestode orders, 13 have been recorded in South America, with the Onchoproteocephalidea displaying the highest species richness, representing c. 50% of all species diversity. The majority of records include teleost fish hosts (79%) that harbour larval and adult stages of cestodes, whereas stingrays (Myliobatiformes) exhibit the highest proportion of records (39%) among the elasmobranch hosts. Fish cestodes are ubiquitous in South America, being mostly recorded from the Warm Temperate Southeastern Pacific (WTSP; 31%) for marine hosts and the Amazon River basin (45%) for freshwater ones. The following problems were detected during the compilation of literary data: (i) unreliability of many records; (ii) poor taxonomic resolution, i.e. identification made only to the genus or even family level; (iii) doubtful host identification; Alves et al. / ZooKeys 650: 1-205 (2017) 2 and (iv) the absence of voucher specimens that would enable us to verify identification. It is thus strongly recommended to always deposit representative specimens in any type of studies, including faunal surveys and ecological studies. An analysis of the proportion of three basic types of studies, i.e. surveys, taxonomic and ecological papers, has shown a considerable increase of ecological studies over the last decade.

Proteocephalid tapeworms are the dominant group of endoparasites in siluriform catfishes in South America, but their interrelationships and actual diversity remain poorly understood. Molecular prospecting of proteocephalids found in pimelodid and other catfishes, especially in Pimelodus spp., along with thorough morphological evaluation, revealed high species diversity of these parasites. Using newly obtained sequences of the partial large subunit nuclear ribosomal RNA (lsrDNA) and complete mitochondrial cytochrome c oxidase subunit I (COI), phylogenetic relationships of the cestodes of Pimelodus catfishes were assessed and a new genus, Pseudoendorchis gen. n., proposed to accommodate P. auchenipteri comb. n. (type species; formerly Endorchis auchenipteri), P. cristata sp. n. from Pimelodella cristata (Heptapteridae), P. felipei sp. n. from Pimelodus fur, P. souzalimae sp. n. from Pimelodus maculatus and another three putative new species. Members of the new genus can be readily distinguished from all known Neotropical proteocephalids by having a large Mehlis’ gland, representing at least 18% of proglottid width, and the vagina always anterior to the cirrus‐sac. Moreover, all phylogenetic, species discovery and validation analyses support validity of Pseudoendorchis. Combining the lsrDNA + COI sequence data appeared to provide the best resolution in phylogenetic analyses, which may be useful to reduce the uncertainty of the interrelationships among Neotropical proteocephalids.

Physaloptera tupinambae n. sp. (Nematoda: Physalopteridae) collected from the stomach of 1 Tupinambis merianae (Squamata: Teiidae) male lizard is described. Physaloptera tupinambae, which belongs to the didelphys group, is the only species in the genus that exhibits a bipartite internal tooth and in which the excretory pore is anterior to the deirids. The new species can be differentiated from the other congeners mainly based on the number and pattern of caudal papillae and the length and shape of spicules. Physaloptera murisbrasiliensis and Physaloptera clausa orientalis are the only physalopterids with the same number of caudal papillae as for P. tupinambae, but they differ from the new species mainly in length and shape of spicules. Based on morphological analysis, the speciation process among Physaloptera probably occurred via host capture, and P. tupinambae occupies an intermediate phylogenetic position in the genus. Most likely, the new parasite was acquired by the lizard through ingestion of an intermediate host. Finally, Physaloptera calotisi, Physaloptera funambuli, Physaloptera guptae, Physaloptera indica, Physaloptera johnsoni, Physaloptera kherai, and Physaloptera thaparus are moved to Abbreviata.

Physaloptera bainae n. sp. (Nematoda: Physalopteridae) from stomach of the large "tegú" lizard Salvator merianae (Squamata: Teiidae), collected in an ecological park that is part of the Atlantic Rainforest biome in Juiz de Fora, Minas Gerais, Brazil, is described. The new species which has females with didelphic uterus, is the only species of the genus exhibiting external teeth in the form of 4 spines that are organized in a cross-shaped pattern at the anterior apical end, with 2 minute adcloacal papillae on the anterior part of cloacal aperture in males and a large cuticular expansion at the anterior end of females. Moreover, P. bainae n. sp. can be differentiated from the other congeners by the combination of other features, e.g., number (23) and pattern of caudal papillae, spicule size (left 554-600; right 589-617) and vulval position (on the first third of body), and because the specimens are particularly large and robust. Physaloptera monodens is considered a junior synonym of P. obtusissima. In addition, a key to Physaloptera species parasitizing reptiles from Brazil is provided.

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