Demonstrating the value and importance of combining DNA barcodes and discriminant morphological characters for polystome taxonomy (Platyhelminthes, Monogenea)

Revision of the systematics of the Polystomoidinae (Platyhelminthes, Monogenea, Polystomatidae) with redefinition of Polystomoides Ward, 1917 and Uteropolystomoides Tinsley, 2017

Polystomatids are platyhelminth parasites that infect mainly amphibians and freshwater turtles. For more than seven decades, chelonian polystomes were classified into three genera according to the number of hamuli, i.e. absent for Neopolystoma, one pair for Polystomoidella and two pairs for Polystomoides. Following re-examination of morphological characters, seven new genera were erected the past six years, namely Apaloneotrema, Aussietrema, Fornixtrema, Manotrema, Pleurodirotrema, Uropolystomoides and Uteropolystomoides. However, the polyphyly of Neopolystoma and Polystomoides on the one hand, and the nested position of Uteropolystomoides within a clade encompassing all Neopolystoma and Polystomoides spp. on the other, still raised questions about the validity of these genera. We therefore re-examined several types, paratypes and voucher specimens, and investigated the molecular phylogeny of polystomes sampled from the oral cavity of North American turtles to re-evaluate their systematic status. We show that all Polystomoides Ward, 1917, sensu Du Preez et al., 2022, Neopolystoma Price, 1939, sensu Du Preez et al., 2022 and Uteropolystomoides Tinsley, 2017 species, display vaginae that are peripheral and extend well beyond the intestine. We thus reassign all species of the clade to Polystomoides and propose nine new combinations; however, although Uteropolystomoides is nested within this clade, based on its unique morphological features, we propose to keep it as a valid taxon. Polystomoides as redefined herein groups all polystome species infecting either the oral cavity or the urinary bladder of cryptodires, with peripheral vaginae and with or without two pairs of small hamuli. Uteropolystomoides nelsoni (Du Preez & Van Rooyen 2015), originally described from Pseudemys nelsoni Carr is now regarded as Uteropolystomoides multifalx (Stunkard, 1924) n. comb. infecting three distinct Pseudemys species of North America.

Classification of pleurodire polystomes (Platyhelminthes, Monogenea, Polystomatidae) revisited with the description of two new genera from the Australian and Neotropical Realms

Polystomatids are platyhelminth parasites that infect mostly amphibian and chelonian hosts. Polystomatid of testudines were, for more than seven decades, classified in the three genera – Neopolystoma Price, 1939, Polystomoides Ward, 1917 and Polystomoidella Price, 1939. The genus delimitation was primarily based on the absence of hamuli in Neopolystoma, the presence of one pair of hamuli in Polystomoidella, and two pairs in Polystomoides. From 2016 to 2020, five new genera were erected - namely Uropolystomoides Tinsley and Tinsley, 2016, Uteropolystomoides Tinsley, 2017, Apaloneotrema Du Preez and Verneau, 2020, Aussietrema Du Preez and Verneau, 2020 and Fornixtrema Du Preez and Verneau, 2020. The generic diagnosis was based not only on the size and shape of morphological characters such as hamulus 1, uterus and eggs, but also on the site of infestation (i.e. urinary bladder, oral cavity or conjunctival sacs). Despite large advancements in polystome classification over the last decade, Neopolystoma was still polyphyletic with some species nested within Polystomoides and others being closely related to the Australian Aussietrema. Regarding the distribution of freshwater turtles of the two suborders Pleurodira (Southern continents) and Cryptodira (distributed worldwide except in Australia), one may wonder whether Australian chelonian polystomes of the genus Neopolystoma may have diverged from species infecting other pleurodires of South America. In the present study based on the analysis of several species selected among all genera, we reveal striking morphological differences within polystomes infecting pleurodiran turtles, which herein led to the proposal of two new chelonian polystome genera, Pleurodirotrema n. g. and Manotrema n. g. Pleurodirotrema n. g. is characterized by the absence of hamuli, presence of latero-ventral vaginae and includes species that infect either the oral region or the urinary bladder of Australian hosts of the Pleurodira. Manotrema n. g. is characterized by the presence of small hamuli, latero-ventral vaginae, deep incisions between suckers, a low genital spine number (<10) and includes species that infect the oral region of South American Pleurodira.

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Two new polystome genera are described from chelonian hosts.

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They differ from all other chelonian polystomes in that they only infect pleurodire turtles from the Australian and Neotropical Realms.

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Describing these two genera resolves a polyphyletic clade as pointed out by Heritier and others.

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Solid morphological characters are supported by molecular evidence for Pleurodirotrema.

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Haptor and suckers for Manotrema are unique among chelonian polystomes.

Under the radar: co-introduced monogeneans (Polyopisthocotylea: Gastrocotylinea) of the invasive fish Scomberomorus commerson in the Mediterranean Sea

The Levant Basin is in many ways the world's most invaded marine ecosystem owing to the existence of the man-made Suez Canal. The invasion of free-living organisms through this pathway is increasingly documented and monitored in the past two decades, and their ecological impact recognized. Nonetheless, while tremendous scientific effort is invested in documenting introduced fishes, co-introduction events of these fishes and their parasites have drawn relatively little interest. In our research, we examined the presence of gill parasites (Monogenea) on the invasive narrow barred Spanish mackerel Scomberomorus commerson which has been known in the Mediterranean Sea for 80 years. The gills of S. commerson supported numerous, relatively large monogeneans (Monogenea: Gastrocotylinea), reaching prevalence levels of 100% with a mean intensity of ~ 80 worms per host. Using an integrated molecular and morphological approach, four gastrocotylinean species were identified: Gotocotyla acanthura, Cathucotyle cathuaui, Pricea multae, and Pseudothoracocotyla ovalis. Two species, C. cathuaui and P. ovalis, are reported here for the first time from the Mediterranean. Sequences of the 28S rRNA gene of G. acanthura from native hosts, Pomatomus saltatrix and Trachinotus ovatus, differed from individuals collected from S. commerson by 1.8%. We therefore suggest that the taxonomic status and distribution of G. acanthura should be revisited, and we recommend an integrated approach as essential to accurately detect co-introductions.

Polystoma luohetong n. sp. (Monogenea: Polystomatidae) from Rana chaochiaoensis Liu (Amphibia: Ranidae) in China

Polystoma chaochiaoensis from the urinary bladder of the chaochiao frog Rana chaochiaoensis Liu was briefly described in a symposium abstract and presented at the Third Symposium on Parasitology of China in 1990. Types were not assigned and the original specimens collected are no longer available. The morphological description was incomplete and no illustrations were provided. We consider Polystoma chaochiaoensis a nomen nudum and provide a full description for the species and assign types. Based on morphological characteristics and molecular data of partial 18S rDNA sequences, we describe this species as Polystoma luohetong n. sp. Out of 578 frogs examined, 16 male and 38 female frogs were infected (prevalence 9.3%; mean intensity 1.02). Polystoma luohetong n. sp. is distinguished from all other Polystoma species by the presense of a prominent crest on the hamulus as well as by the shape and size of marginal hooklets and the intestinal arrangement. Furthermore, the phylogentic analysis based on the 18S rRNA gene shows Polystoma luohetong n. sp. well nested within the Ploystoma clade and as a sister taxon to Polystoma integerrimum.

Indopolystoma n. gen. (Monogenea, Polystomatidae) with the description of three new species and reassignment of eight known Polystoma species from Asian frogs (Anura, Rhacophoridae)

The polystomes (Monogenea, Polystomatidae) radiated across semi-aquatic tetrapods including all three amphibian orders, freshwater turtles and the hippopotamus. Prior to this study, phylogenetic analyses revealed that the most diverse and widespread genus, Polystoma, was not monophyletic; a lineage comprising four undescribed species from the bladder of Zhangixalus spp. (Rhacophoridae) in Asia occupied a deep phylogenetic position. Regarding vicariance biogeography and molecular dating, the origin of this lineage is correlated with the breakup of Gondwanaland in the Mesozoic period. Based on a Bayesian analysis of four concatenated genes (18S, 28S, COI and 12S) and morphological evidence, one new genus, Indopolystoma n. gen., and three new species, sampled in Japan and China, are described here: Indopolystoma viridi n. sp. from Z. viridis of Japan, Indopolystoma elongatum n. sp. from Z. arboreus of Japan, and Indopolystoma parvum n. sp. from Z. omeimontis of China. Indopolystoma is unique amongst polystome genera infecting anurans by possessing a small haptor relative to the body size, posteriormost marginal hooklet C1 much bigger than hooklets C2–C8 with conspicuous broad blade and guard and a pair of hamuli lacking a deep notch. Eight species of Asian Polystoma, all from rhacophorids, are transferred as Indopolystoma carvirostris (Fan, Li & He, 2008) n. comb., I. hakgalense (Crusz & Ching, 1975) n. comb., I. indicum (Diengdoh & Tandon, 1991) n. comb., I. leucomystax (Zhang & Long, 1987) n. comb., I. mutus (Meng, Song & Ding, 2010) n. comb., I. pingbianensis (Fan, Wang & Li, 2004) n. comb., I. rhacophori (Yamaguti, 1936) n. comb., and I. zuoi (Shen, Wang & Fan, 2013) n. comb.

Two new species of Acanthocotyle Monticelli, 1888 (Monogenea: Acanthocotylidae), parasites of two deep-sea skates (Elasmobranchii: Rajiformes) in the South-East Pacific

Background

Parasites of deep-sea fishes from the South-East Pacific (SPO) are poorly known. Of c.1030 species of fish found in this area, 100–150 inhabit the deep-sea (deeper than 200 m). Only six articles concerning metazoan parasites of fish from deep-waters of SOP are known, and nine monogenean species have been reported. Currently, ten species are known in Acanthocotyle Monticelli, 1888 (Monogenea) and when stated, all of them are found in shallow waters (10–100 m). Acanthocotyle gurgesiella Ñacari, Sepulveda, Escribano & Oliva, 2018 is the only known species parasitizing deep-sea skates (350–450 m) in the SPO. The aim of this study was the description of two new species of Acanthocotyle from two Rajiformes.

Methods

In September 2017, we examined specimens of two species of deep-sea skates (Rajiformes), Amblyraja frerichsi (Krefft) and Bathyraja peruana McEachran & Myyake, caught at c.1500 m depth off Tocopilla, northern Chile, as a by-catch of the Patagonian tooth fish Dissostichus eleginoides Smitt fishery. Specimens of Acanthocotyle were collected from the skin of the skates. Morphometric (including multivariate analysis of proportional measurements, standardized by total length), morphological and molecular analyses (LSU rRNA and cox1 genes) were performed in order to identify the collected specimens.

Results

The three approaches used in this study strongly suggest the presence of two new species in the genus Acanthocotyle: Acanthocotyle imo n. sp. and Acanthocotyle atacamensis n. sp. parasitizing the skin of the thickbody skate Amblyraja frerichsi and the Peruvian skate Bathyraja peruana, respectively. The main morphological differences from the closely related species Acanthocotyle verrilli Goto, 1899 include the number of radial rows of sclerites, the non-discrete vitelline follicles and the number of testes.

Conclusions

The two species of monogeneans described here are the only recorded parasites from their respective host species in the SPO. Assessing host specificity for members of Acanthocotyle requires clarifying the systematics of Rajiformes.