Maria Naiane Martins de Carvalho

Anacanthorus is one of the most diverse genera of monopisthocotyl parasites associated with Neotropical Characiformes, particularly serrasalmid fishes. This study aimed to inventory the monopisthocotyl parasites of serrasalmid fish from the Lower São Francisco River, northeastern Brazil. Twenty-nine specimens of Pygocentrus nattereri were collected, and their parasites were examined using standard morphological methods. Our results allowed the description of Anacanthorus penedensis n. sp., supported by morphological and molecular data, and the assessment of its phylogenetic relationships within the Dactylogyridae using partial 28S rDNA sequences. Additionally, previously described monopisthocotyls are reported, including Anacanthorus reginae , Amphithecium falcatum , and Enallothecium aegidatum , whereas Rhinoxenus sp. was identified to the genus level and another dactylogyrid remained unidentified. Anacanthorus penedensis n. sp. can be distinguished from its congeners by having an accessory piece comprising two distinct expansions: a submedial expansion extending to the distal region and a conspicuous laminar subterminal expansion originating from one of the margins of the shaft, with a hooked acute tip, as well as by the relative lengths of the male copulatory organ and the accessory piece. Phylogenetic analyses of 28S rDNA sequences, based on maximum likelihood and Bayesian inference, placed the new species within the genus Anacanthorus and supported the monophyly of the group based on the dataset used in the present study. These findings reinforce the need for future integrative taxonomic studies that combine complementary lines of evidence for species delimitation and suggest the diversity of Anacanthorus remains underestimated.

Based on morphological and molecular data, we describe a new species of Diaphorocleidus parasitizing the nasal cavities of Tetragonopterus argenteus from the Lima Campos weir, municipality of Icó, state of Ceará, Brazil. Diaphorocleidus radius n. sp. resembles other congeners in the morphology of the accessory piece, all by having a bifurcated accessory piece (pincer-shaped), composed of two subunits articulated. However, the new species can be easily distinguished from all congeners by the morphology of the sclerotized structures of the haptor (ventral anchor with well-developed superficial root, ornamented deep root, recurved blade, elongated and lightning-shaped tip; and ventral bar robust, plate-shaped, truncated in lateral ends). Phylogenetic analyses of LSU rDNA and COI mtDNA sequences, conducted using Bayesian Inference and Maximum Likelihood, placed Diaphorocleidus radius n. sp. within Diaphorocleidus , grouping it with species parasitizing acestrorhamphid hosts. Genetic distances between Diaphorocleidus radius n. sp. and other congeneric species such as D. armillatus and D. forficata showed clear differentiation. Both molecular markers support the distinctiveness of Diaphorocleidus radius n. sp., consistent with its recognition as a new taxon.

Leporinus piau is a freshwater fish belonging to the family Anostomidae, popularly known as "piau" in Brazil. This species has wide distribution in Brazilian northeast basins and presents an economic and sporting fishing importance. The present study aims to inventory the parasitofauna of L. piau of a freshwater ecosystem of Caatinga domain (Brazil). A total of 598 parasite specimens were recovered from nine parasitized hosts, belonging to four taxonomic groups: one Myxozoa (Henneguya sp.); four Monogenea (Dactylogyridae gen. sp., Jainus sp., Urocleidoides sp. 1 and Urocleidoides sp. 2); one Nematoda (Procamallanus (Spirocamallanus) inopinatus) and two Copepoda (Ergasilus sp. and Gamispatulus schizodontis). Previous studies reported five parasitic associations in L. piau: two nematodes (P. (S.) inopinatus and Procamallanus (Spirocamallanus) saofrancicencis) and three crustaceans (Argulus sp., Brasergasilus sp. and Ergasilus sp.). For the first time, this study records myxozoan and monogeneans parasitizing the host L. piau. The present study stands out the importance of the knowledge of the parasite biodiversity of freshwater fish in neotropics, reporting new occurrences and parasitic association for ichthyofauna of the Caatinga domain.

The present study is the first report of Spiroxys larvae parasitizing stomach and intestine of three fish species in stream of Caatinga domain, Northeast, Brazil. A total of 120 fish specimens, 40 of Astyanax bimaculatus, 40 of Hoplias malabaricus, and 40 of Hoplosternum littorale were examined for nematodes. A total of 633 specimens of Spiroxys larvae were recovered for the three fish species: 227 in A. bimaculatus (prevalence (%) = 48; mean abundance = 5.78 ± 1.78 (range = 0-70); and mean intensity = 11.95 ± 2.7 (range = 2-70)), 176 in H. malabaricus (prevalence (%) = 42.5; mean abundance = 4.40 ± 1.55 (range = 0-53); and mean intensity = 10.35 ± 2.38 (range = 2-53)) and 230 in H. littorale (prevalence (%) = 42.5; mean abundance = 5.75 ± 1.98 (range = 0-52); and mean intensity = 13.53 ± 3.04 (range = 1-52)). This study expands the range of the geographic distribution of nematodes of the genus Spiroxys and increase the list of hosts, as well as contributing to the knowledge of fish parasites biodiversity in Caatinga domain.