Dora Davies

The genus Polystoma includes parasites with direct life cycles that involve a short-lived free-living, aquatic oncomiracidia, post-larvae infecting the gill chambers of tadpoles, and adults parasitizing the urinary bladder of adult anurans. Despite the high diversity of anurans in the South American sub-continent, less than 20 species of Polystoma have been reported to date, and, particularly, in Argentina, only five species have been described from adult frogs. The aim of this work was to describe and characterize taxonomically the specimens found parasitizing tadpoles and frogs living in a well in Chicoana, Salta province, Argentina. Parasites were observed under optical and scanning electron microscopy and characterized genotypically by sequencing ITS1 and COI fragments. Frogs and tadpoles were characterized by morphology and sequencing a partial fragment of the cytochrome B region, confirming that the hosts corresponded to Pleurodema borellii. Given their morphology and the strict specificity of Polystoma species for their hosts, the identity of the parasites was established as P. borellii. The morphology of oncomiracidia and post-larvae was described, expanding adults’ description with insights provided by COI and ITS1 molecular analysis. The present work summarizes a complete description of the life cycle, with the genetic characterization of Polystoma borellii in Salta, Argentina.

Auriculostoma is a genus of digenean (Trematoda) whose adults are parasites of Neotropical freshwater fishes. We describe Auriculostoma ocloya n. sp. using morphological and molecular tools, and we elucidated its life cycle, the first known of a species of this genus. The first intermediate host is the bivalve Pisidium ocloya, the second intermediate host is the amphipod Hyalella sp., and the definite hosts are siluriform fishes. The adult presents a single pair of muscular lobes on either side of the oral sucker with a broad base, stretching from ventrolateral to dorsolateral side, a structure also present in the rest of species of the genus. Nevertheless, the new species differs from all congeners by the combination of several traits, and mainly because on the dorsal side "free" ends of the lobes are absent because they are fused. This is the first study to provide sequence data on larval and adult stages of a species of Auriculostoma. Our phylogenetic analysis demonstrated its basal position among species of the genus. Therefore, integrative morphological, molecular, and life cycle data on other South American species of the genus, would contribute to reveal more patterns in the allocreadiid systematics.

We describe the alloglossiid trematode Magnivitellinum saltaensis n. sp., a parasite of the characiform fish Psalidodon endy, and its life cycle from Salta, northwest of Argentina. This is the first life cycle described for a species belonging to the genus Magnivitellinum. Cercariae emerged naturally from Biomphalaria tenagophila snails and infected experimentally exposed larvae of Diptera and Ephemeroptera as second intermediate hosts. These larvae in turn were exposed to commercially raised fish, and adults were recovered from characiform albino fish Gymnocorymbus ternetzi. Molecular analysis of natural and experimental adults showed the same genetic sequence for the partial region of 28S rDNA, thus confirming conspecificity. Comparison of these sequences with those published for M. simplex from Mexico showed 1.45% divergence, indicating that the specimens found in Salta belong to a different species, the third described of Magnivitellinum, in agreement with morphological data, geographical location, and host species composition. The new species is distinguished by its small body, vitelline follicles extending from the mid-level of the ventral sucker, Y-shaped excretory vesicle, and presence of papillae around the mouth.