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In this study, we compared the efficacy of geometric morphometric techniques, including outlines and landmark-based approaches, to support the differentiation of Trichodina bellottii from three co-occurring killifish species. Both methods were able to differentiate trichodinids from different host species. However, discriminat analyses and MANOVA results based on landmarks had greater accuracy possibly because these analyses only provide information on certain points defined by the researcher, while the analyses based on outlines take into account points with less taxonomic information.

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Trichodina centrostrigeata Basson, Van As et Paperna, 1983 from Oreochromis mossambicus (Peters) and O. niloticus (Linnaeus) from different host populations from Argentina, Mexico and South Africa was reviewed. Although T. centrostrigeata has a distinct denticle structure that makes morphological taxonomic inferences uncomplicated, variation of the denticles within and among individuals and populations were still observed. While traditional taxonomy of mobilines is heavily reliant on morphometrics, and recently even more so on molecular analysis, this paper proposes the use of geometric morphometry, specifically elliptical Fourier analysis, to address morphological conflicts that arise when comparing different populations. By applying this technique, combined with traditional taxonomy, it was found that T. centrostrigeata in this study can be grouped into two separate morphotypes, the first (type a) from aquaculture farms in Argentina and Mexico and the second (type b) from a natural habitat in Glen Alpine Dam, South Africa. This study supports the validity of geometric morphometry as an additional technique to distinguish not only between species but also evolutionary plasticity of the same species from different localities and habitats.

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The finding of Pomphorhynchus sphaericus in new localities from La Plata River allowed the reevaluation of the species using a taxonomic integrative approach. The newly found specimens in Pimelodus maculatus from Samborombon Bay differ from P. sphaericus by the roots of hooks 1-6 which not form a wide sheet split into 2 apophysis, the slender, separated and equatorial testicles, the position of the cement glands, the shape of the proboscis, the shape and length of lemnisci, and the eggs size. Despite the notorious observed morphological differences, the COI mtDNA analysis confirmed that Pomphorhynchus individuals are the same conspecific, and showed that there is a high phenotypical plasticity in this species. Pomphorhynchus sphaericus is the first South American species analyzed to a DNA level (COI mtDNA, ITS, and 18S rDNA genes). The molecular analysis relates P. sphaericus to P. bulbocolli and P. purhepechus.

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Tilapia is the common name for a wide spectrum of cichlid fishes usually selected for aquaculture activities. However, some aspects of the natural history of these fishes, such as the diversity of certain ectoparasitic protistan groups remain understudied. In order to understand the diversity of ciliates of the family Trichodinidae parasitizing tilapia around the world, a database with all available accounts was assembled. This information, along with records derived from our own recent research, allowed us to generate a checklist containing all the records for tilapia-Trichodinidae associations. The checklist is presented as a host-parasite list containing 44 nominal taxa from 29 countries on four continents, and it also presents the first data from Argentina, where tilapia culture is still an incipient, but growing activity. The observed high species richness of trichodinids is probably derived from a set of specific taxa for tilapia, along with an important component of species acquired from the new environments where tilapia have been introduced. Data presented here could be used along with existing information of metazoan parasites to build a general view about diseases that affect tilapia.

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This study reports a new Trichodinidae, Trichodina bellottii n. sp., parasitizing the pearly fish Austrolebias bellottii from Buenos Aires, Argentina. Its small subunit ribosomal ribonucleic acid (SSU rDNA) was sequenced for the first time. Based on the results from morphological identification, SSU rDNA sequencing, and Elliptical Fourier analysis, the new species was identified and compared with similar species. Phylogenetic analysis revealed that the genetic distances among the new species and similar species reached interspecific levels, furthermore, the phylogenetic study also validated the identification of T. bellottii n. sp. and its placement in the genus Trichodina. To be able to quantitatively describe the differences in shapes with similar species, this study used the elliptic Fourier analysis by first time in this genus.

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In this paper, we describe two new species of Syndesmis living in Pseudechinus magellanicus in the Southwest Atlantic Ocean. The new species have a long stylet in the male reproductive system, which is different from that of the known species of the genus. Specimens of Syndesmis selknami n. sp. have a ∼220-µm-long stylet (∼1/3 of the body length, 0.69 mm). This ratio is unique because only four species (Syndesmis echinorum, Syndesmis rubida, Syndesmis inconspicua and Syndesmis echiniacuti) have similar stylet lengths but are larger in body sizes (3-5 mm). Specimens of Syndesmis aonikenki n. sp. have a ∼148-µm-long stylet (∼1/10 of the body length, 1.11 mm). Syndesmis pallida has a similar ratio but the uterus is located posteriorly, and the filament glands are very small and located in the posterior region of the body. These are the first flatworms reported parasitizing Pseudechinus magellanicus.

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Myxosporean Myxobolus saladensis sp. nov. in the gills of Mugil liza Valenciennes, 1836 from Samborombón Bay was described by light and electron microscopy studies. Spores were pyriform and binucleated, measuring 10.63±0.36 µm (n=20) long, 9.24±0.50 µm (n=20) wide and 4.13±0.36 µm (n=20) thick, included in polysporic cyst-like plasmodia. Elongated pyriform polar capsules were of equal size (3.84±0.27 µm long and 2.30±0.12 µm wide). The sporoplasm contained some sporoplasmosomes. Each PC contained a polar filament with 4-5 coils obliquely arranged in relation to the polar capsules axis. The PC wall was composed of two layers of different electron densities. Based on the morphological and ultrastructure differences of the spore to those of previously described species of Myxobolus, we describe a new species, Myxobolus saladensis sp. nov.

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ABSTRACT Myxosporean Myxobolus saladensis sp. nov. in the gills of Mugil liza Valenciennes, 1836 from Samborombón Bay was described by light and electron microscopy studies. Spores were pyriform and binucleated, measuring 10.63±0.36 µm (n=20) long, 9.24±0.50 µm (n=20) wide and 4.13±0.36 µm (n=20) thick, included in polysporic cyst-like plasmodia. Elongated pyriform polar capsules were of equal size (3.84±0.27 µm long and 2.30±0.12 µm wide). The sporoplasm contained some sporoplasmosomes. Each PC contained a polar filament with 4-5 coils obliquely arranged in relation to the polar capsules axis. The PC wall was composed of two layers of different electron densities. Based on the morphological and ultrastructure differences of the spore to those of previously described species of Myxobolus, we describe a new species, Myxobolus saladensis sp. nov.

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Myxosporean Myxobolus saladensis sp. nov. in the gills of Mugil liza Valenciennes, 1836 from Samborombón Bay was described by light and electron microscopy studies. Spores were pyriform and binucleated, measuring 10.63±0.36 µm (n=20) long, 9.24±0.50 µm (n=20) wide and 4.13±0.36 µm (n=20) thick, included in polysporic cyst-like plasmodia. Elongated pyriform polar capsules were of equal size (3.84±0.27 µm long and 2.30±0.12 µm wide). The sporoplasm contained some sporoplasmosomes. Each PC contained a polar filament with 4-5 coils obliquely arranged in relation to the polar capsules axis. The PC wall was composed of two layers of different electron densities. Based on the morphological and ultrastructure differences of the spore to those of previously described species of Myxobolus, we describe a new species, Myxobolus saladensis sp. nov.(AU)

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During surveys of parasites of the whitemouth croaker Micropogonias furnieri (Desmarest) and the mullet Mugil platanus Günther from Samborombón Bay, Argentina, Trichodina puytoraci, T. lepsii, T. jadranica, T. murmanica, Diparitella simplex and Trichodina scalensis sp. n. were morphologically studied. Taxonomic and morphometric data for these trichodinids based on dry silver nitrate-impregnated specimens are presented. This study is the first formal report of these trichodinids from the southwest Atlantic Ocean, and the description of a new species from M. platanus.

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Ligophorus saladensis n. sp. (Monogenea: Dactylogyridae) is described from the gills of the grey mullet Mugil platanus Günther collected in Samborombón Bay, Argentina. The new species differs from L. mugilinus Euzet & Suriano, 1977, L. mediterraneus Sarabeev, Balbuena & Euzet, 2005 and L. huitermpe Fernandez, 1987 by the morphology of the accessory piece of the male copulatory organ and mean values derived from measurements of the sclerotised hard-parts. This is the second report of monogeneans on M. platanus in the Southwestern Atlantic Ocean region and the first description of a species of Ligophorus Euzet & Suriano, 1977 from M. platanus. Some aspects of the speciation and host-specificity of Ligophorus spp. are discussed.

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