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Cystacanths of the polymorphid acanthocephalan Corynosoma evae Zdzitowiecki, 1984 were examined and redescribed based on newly collected material from teleost fishes from coastal waters of the Galindez Island (Argentine Islands, West Antarctica). Detailed morphological data, measurements and photomicrographs, including scanning electron microscopy images, are presented. Our morphological and morphometrical analyses confirmed the validity of C. evae; however, three key characteristics of taxonomic importance (i.e., the number of rows of hooks on the proboscis, and the number and arrangement of genital spines in males) showed significant morphological variability. In addition, a genital spine in the posterior body end of a female is reported for the first time. This study provides the first sequences of the small and large subunits nuclear ribosomal RNA genes (SSU and LSU) and the mitochondrial cytochrome c oxidase subunit 1 (cox1) for C. evae. Maximum likelihood and Bayesian inference analyses of the SSU + LSU + cox1 and the cox1 datasets placed C. evae as a sister lineage to a clade formed by C. validum Van Cleave, 1953 and C. villosum Van Cleave, 1953, although with low support. In contrast, the position of C. evae in the phylogenetic analysis of the SSU + LSU dataset remained unresolved. Finally, C. arctocephali Zdzitowiecki, 1984 from pinnipeds from the subantarctic and Antarctic regions is considered as a valid species.

We described two novel myxozoan parasite species Ceratomyxa argentina n. sp. and Ceratomyxa raneyae n. sp. from the gall bladder of Raneya brasiliensis (Kaup) from the Patagonian coast of Argentina. Both species can be distinguished from other ceratomyxids by myxospore and polar capsule (nematocyst) morphology and morphometry, fish host and geographic locality. Phylogenetic reconstruction using ssrDNA gene sequences showed that the two new species are placed in a long-branching ceratomyxid clade which also include Ceratomyxa appendiculata Thelohan, 1892, Ceratomyxa anko Freeman, Yokoyama and Ogawa, 2008, Ceratomyxa pantherini Gunter, Burger and Adlard, 2010 and Pseudoalataspora kovalevae Kalavati, MacKenzie, Collins, Hemmingsen and Brickle, 2013. This study documents additional biodiversity of marine myxozoans in the South Atlantic, a region still largely unexplored for this group of parasitic cnidarians.

Adult specimens of Corynosoma australe Johnston, 1937 were recorded from the intestines of California sea lions, Zalophus californianus (Lesson), from Baja California Peninsula, Mexico, whereas larval forms were collected from two fish species on the Argentinian coast. Adult specimens of C. australe were morphologically characterized by having a cylindrical proboscis with 18–20 rows of 12–14 hooks per row and a cylindrical trunk expanded anteriorly into a disk with tiny, triangular spines spreading almost to three quarters of the hind-trunk in males and to the posterior body end in females. The aim of this study was to explore the genetic diversity and systematic position of C. australe distributed in the Americas. Newly generated sequences of the mitochondrial cytochrome c oxidase subunit 1 (cox 1) gene were compared with sequences available from GenBank. Phylogenetic analyses performed with the cox 1 dataset using maximum likelihood and Bayesian inference showed that the 11 new sequences of C. australe recovered from the California sea lion in northern Mexico plus the six sequences from Argentinian seashores formed a clade with other sequences of specimens previously identified as C. australe. The intraspecific genetic divergence among the isolates was very low, ranging from 1 to 1.7%, and in combination with the phylogenetic trees confirmed that the isolates belonged to the same species. The cox 1 haplotype network inferred with 27 sequences revealed 18 haplotypes divided into two clusters clearly separated from each other by 5 substitutions. The first cluster corresponded to specimens from the Northern Hemisphere (United States of America and Mexico), and the second corresponded to specimens from the Southern Hemisphere (Argentina and Brazil). The current evidence suggests that C. australe has an amphitemperate distribution and is associated mainly with otariids with secondary and independent colonization events to other mammals and the Magellanic penguin in the Southern Hemisphere.

Pseudocorynosoma tepehuanesi n. sp., is described from the intestine of the ruddy duck Oxyura jamaicensis Gmelin, 1789 from single locality from northern Mexico. The new species is mainly distinguished morphologically from the other five described species of Pseudocorynosoma from the Americas (P. constrictum, type species, P. peposacae, P. anatarium, P. enrietti and P. iheringi) associated with waterfowl species by possessing a proboscis with 15 longitudinal rows with 7–8 hooks each, a trunk expanded anteriorly and by having smaller lemniscus. Partial sequences of the mitochondrial gene cytochrome c oxidase subunit I (cox 1) and the large subunit (LSU) of ribosomal DNA including the domains D2 + D3 were used independently to corroborate the morphological distinction between the new species and other two congeneric species (P. constrictum and P. anatarium) from North America. The genetic divergence estimated among the new species and the other two species ranged from 15 to 18% for cox 1 and from 3.2 to 4% for LSU. The cox 1 alignment shows 24 sequences from P. anatarium with abnormalities, which were defined as pseudogenes due the presence of insertions, deletions and premature stop codons. Maximum likelihood and Bayesian inference analyses with each data set showed that the acanthocephalans from ruddy duck represent an independent clade with strong bootstrap support and posterior probabilities. The phylogenetic tree inferred with cox 1 gene placed all the pseudogenes from P. anatarium in single clade suggesting that those genes arose after speciation process within genus Pseudocorynosoma. The morphological evidence, plus the monophyly in both phylogenetic analyses indicate that the acanthocephalans collected from intestine of the ruddy duck from northern Mexico represent a new species. Fil: García Varela, Martín. Universidad Nacional Autónoma de México; México Fil: Hernández Orts, Jesús Servando. Universidad Nacional del Comahue. Instituto de Biología Marina y Pesquera Almirante Storni; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Pinacho Pinacho, Carlos D.. Universidad Nacional Autónoma de México; México. Universidad de la Sierra Sur; México