Integrative Taxonomy Reveals a Panmictic Population of Henneguya longisporoplasma n. sp. (Cnidaria: Myxozoa) in the Amazon Basin.

PURPOSE: Henneguya Thélohan, 1892 is one of the most species-rich genera of myxosporean parasites and infects fish around the world. The present study describes a new species infecting the gill filaments, fins, and kidneys of Plagioscion squamosissimus (Heckel, 1840), an economically important freshwater fish distributed in watersheds in the north of South America. METHODS: A total of 108 P. squamosissimus specimens were examined from three geographic localities in the Amazon basin: the Lago Grande do Curuai, a marginal lake of the Amazon River; the Tapajós River, in the state of Pará; and the Solimões River, in the state of Amazonas, Brazil. The analyses were based on the myxospore morphology, ribosomal DNA sequencing, phylogeny, prevalence, and geographic distribution of the host and its parasite. RESULTS: Parasite prevalences were 50% in both the Tapajós and Solimões rivers, and 35.4% in the Lago Grande do Curuai. In terms of the site of infection, the prevalence total was 23.1% in the gill filament, 29.6% in the fins, and 1.8% in the kidney. Regarding gender, the prevalence was 59.5% for males, 32.5% for females, and 21.7% for undetermined sex. The specimens found here were both morphologically and molecularly identical regardless of the infected organ and geographic locality, but distinct from all other Henneguya species, revealing that the parasite reported represents a novel species named Henneguya longisporoplasma n. sp. Despite the sampling being carried out in three different geographic localities of the Amazon basin, no population-level genetic variation was observed, even in the typically more variable ITS-1 region, revealing a panmictic population of H. longisporoplasma n. sp. in this large watershed. Maximum likelihood and Bayesian analyses showed the novel Henneguya clustered as a sister branch of the subclade formed of Henneguya that infect fish belonging to the family Cichlidae. CONCLUSIONS: A novel Henneguya species was identified parasitizing P. squamosissimus. The parasite presented wide geographic distribution in the Amazon basin and genetic analyses showed it as revealing a panmictic population.

The Phylogenetic Position of the Enigmatic, Polypodium hydriforme (Cnidaria, Polypodiozoa): Insights from Mitochondrial Genomes.

Polypodium hydriforme is an enigmatic parasite that belongs to the phylum Cnidaria. Its taxonomic position has been debated: whereas it was previously suggested to be part of Medusozoa, recent phylogenomic analyses based on nuclear genes support the view that P. hydriforme and Myxozoa form a clade called Endocnidozoa. Medusozoans have linear mitochondrial (mt) chromosomes, whereas myxozoans, as most metazoan species, have circular chromosomes. In this work, we determined the structure of the mt genome of P. hydriforme, using Illumina and Oxford Nanopore Technologies reads, and showed that it is circular. This suggests that P. hydriforme is not nested within Medusozoa, as this would entail linearization followed by recirculation. Instead, our results support the view that P. hydriforme is a sister clade to Myxozoa, and mt linearization in the lineage leading to medusozoans occurred after the divergence of Myxozoa + P. hydriforme. Detailed analyses of the assembled P. hydriforme mt genome show that: (1) it is encoded on a single circular chromosome with an estimated size of ∼93,000 base pairs, making it one of the largest metazoan mt genomes; (2) around 78% of the genome encompasses a noncoding region composed of several repeat types; (3) similar to Myxozoa, no mt tRNAs were identified; (4) the codon TGA is a stop codon and does not encode for tryptophan as in other cnidarians; (5) similar to myxozoan mt genomes, it is extremely fast evolving.

Expanding the geographic distribution of the freshwater parasite Ceratomyxa (Cnidaria: Myxozoa) with vermiform-type plasmodia.

Although species of the genus Ceratomyxa Thélohan, 1892 mostly parasitize marine fish around the world, a surprising diversity of the genus has recently been reported from Amazonian freshwater fish. In this study, we report a freshwater Ceratomyxa species parasitizing Hemiodus orthonops (Hemiodontidae) from the Paraná River (La Plata Basin) in a watershed flowing into the southern part of South America, which expands the geographic distribution of this fish parasite in the freshwater resources of the continent. We applied a combination of morphological, small subunit ribosomal DNA (SSU rDNA), and phylogenetic analyses, and vermiform-shaped plasmodia endowed with motility were found swimming in the bile of the fish. The characteristics of the plasmodia and myxospores of the Ceratomyxa species found in the Paraná River resembled those of Ceratomyxa fonsecai, a parasite of the congeneric host Hemiodus unimaculatus from the Tocantins River basin in northern Brazil. Due to the close morphological and morphometric resemblances and the impossibility of genetic comparison, the parasite found in H. orthonops from the Paraná River was designated as Ceratomyxa cf. fonsecai, and the definition of its taxonomic status was left for further study. Maximum likelihood and Bayesian analyses showed Ceratomyxa cf. fonsecai clustering within a well-supported clade, together with other Amazonian freshwater ceratomyxids. The present study suggests that shifts of the complex host/parasite between marine and freshwater environments were facilitated by marine incursions into South America in the Early Miocene.

Synopsis of the species of Myxobolus (Cnidaria, Myxozoa, Myxosporea) described between 2014 and 2020.

A synopsis of the species of Myxobolus Bütschli, 1882 (Cnidaria, Myxosporea, Myxobolidae) described from 2014 up till now is presented. It includes 122 nominal species described all over the world. For each of the species, the most relevant morphological and morphometric data, as well as data are provided related to the location in the host, type host and type locality. The GenBank accession numbers are provided whenever possible, and the spores were redrawn based on the original descriptions. The bibliography includes all the papers containing the species descriptions.

Taxonomy and 18S rDNA-based phylogeny of Henneguya multiradiatus n. sp. (Cnidaria: Myxobolidae) a parasite of Brochis multiradiatus from Peruvian Amazon.

A new myxozoan species belonging to the genus Henneguya was isolated from the serous membrane of the visceral cavity of the hognosed catfish Brochis multiradiatus from Peruvian Amazon. Whitish plasmodia, macroscopically visible, were found in four of the thirty examined fishes. Mature myxospores were ellipsoidal in shape in frontal view and had a total length of 44.5 ± 0.6 µm (43.9-45.1), spore body measured 18.7 ± 0.9 µm (16.8-19.6) in length, 7.1 ± 0.2 µm (6.6-7.4) in width and 5.5 ± 0.3 µm (4.9-5.6) in thickness. The two polar capsules were elongated and equal in size, measuring 9.1 ± 0.1 µm (8.8-9.4) in length and 1.7 ± 0.1 µm (1.6-1.8) in width, occupying half of the myxospore body. Polar tubules coiled in 10-11 turns perpendicular to the long axis of the polar capsule. The caudal appendage was not bifurcated and measured 25.8 ± 0.6 µm (24.7-26.5) in length. The sequencing of the 18S rDNA gene resulted in 1400 bp and this sequence did not match any of the myxozoans available in GenBank. Phylogenetic analysis placed the new species in a well-supported subclade of Henneguya spp. infecting callichthyid fishes, with Henneguya loretoensis being the closest species. This study is the first description of a myxozoan species, Henneguya multiradiatus n. sp. from a fish of the genus Brochis.