The Species Diversity Assessment of Azygia Looss, 1899 (Digenea: Azygiidae) from the Volga, Ob, and Artyomovka Rivers Basins (Russia), with Description of A. sibirica n. sp.

Abstract

This study is devoted to the investigation of Azygia (Digenea: Azygiidae) species diversity using classical morphological, recent molecular tools (28S rRNA and cox1 mtDNA for genetic-based inference) and robust statistical techniques (Principal component analysis, PCA). The analysis revealed that the genus Azygia included four valid species: A. lucii, A. longa, A. hwangtsiyui, and A. sibirica n. sp. The distribution of the type species A. lucii was confirmed in the largest Russian rivers: the Volga and the Ob. The worms isolated from Perccottus glenii were determined as the Chinese species A. hwangtsiyui, according to the genetic data for the cox1 mtDNA gene, at 1.32–1.56%. The new species, Azygia sibirica n. sp, was described from Esox lucius in the Ob River and differentiated from the type species A. lucii by the smaller ovary, testes and prostatic sac, wider body, very narrow pharyngeal lumen and form of anterior margin of ovary. In addition, multivariate analysis and three methods for species delimitation (ABGD, GMYC, bPTP) showed the subdivision of A. lucii and A. sibirica n. sp. into two separate groups, one from the Volga River and another from the Ob River, respectively. To conclude, A. lucii infects Esox lucius in the western (European part of Russia, the Volga River basin), and northern (Western Siberia, the Ob River basin) parts of Russia; A. sibirica n. sp. has also been found to infect Esox lucius in the Ob River, while A. hwangtsiyui infects Perccottus glenii in the South of the Russian Far East (the Artymovka River basin).

A report on the complete mitochondrial genome of the trematode Azygia robusta Odhner, 1911, its new definitive host from the Russian Far East, and unexpected phylogeny of Azygiidae within Digenea, as inferred from mitogenome sequences

“…To date, four species of definitive hosts for trematodes Azygia spp. are known from the Russian Far East: the northern snakehead Channa argus (Cantor, 1842) and the Amur pike Esox reicherti Dybowski, which are freshwater fishes, and the common taimen Hucho taimen (Pallas, 1773) and the Chinese sleeper Perccottus glenii Dybowski, 1877, which are freshwater/brackish-water fishes (Mamaev, Oshmarin, 1971; Dvoryadkin 1977; Ermolenko et al 1998; Besprozvannykh 2005; Vainutis et al 2023). In this study, we have extended the list of definitive hosts for this region by adding the Sakhalin taimen, Parahucho perryi (Brevoort, 1856).…”

“…Representatives of the type genus of this family, Azygia Looss, 1899, possess a characteristic medium- or large-sized, elongated body, a small oral sucker, a large ventral sucker, and two large tandem testes. In the Russian Far East, these worms are known to infect mainly freshwater fishes, including such species as Esox reicherti Dybowski, 1869, Perccottus glenii Dybowski, 1877, Hucho taimen (Pallas 1773), and Channa argus (Cantor, 1842) (Mamaev, Oshmarin, 1971; Dvoryadkin 1977; Ermolenko et al 1998; Besprozvannykh 2005; Vainutis et al 2023). The phylogenetic position of Azygiidae among other members of the Hemiurata is currently under debate.…”