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

New data on the complete mitochondrial genome of Azygia robusta (Azygiidae) were obtained by the next-generation sequencing (NGS) approach. The mitochondrial DNA (mtDNA) of A. robusta had a length of 13 857 bp and included 12 protein-coding genes, two ribosomal genes, 22 transfer RNA genes, and two non-coding regions. The nucleotide sequences of the complete mitochondrial genomes of two A. robusta specimens differed from each other by 0.12 ± 0.03%. Six of 12 protein-coding genes demonstrated intraspecific variation. The difference between the nucleotide sequences of the complete mitochondrial genomes of A. robusta and Azygia hwangtsiyui was 26.95 ± 0.35%; the interspecific variation of protein-coding genes between A. robusta and A. hwangtsiyui ranged from 20.5 ± 0.9% (cox1) to 30.7 ± 1.2% (nad5). The observed gene arrangement in the mtDNA sequence of A. robusta was identical to that of A. hwangtsiyui. Codon usage and amino acid frequencies were highly similar between A. robusta and A. hwangtsiyui. The results of phylogenetic analyses based on mtDNA protein-coding regions showed that A. robusta is closely related to A. hwangtsiyui (belonging to the same suborder, Azygiida) that formed a distinct early-diverging branch relative to all other Digenea. A preliminary morphological analysis of paratypes of the two azygiid specimens studied showed visible morphological differences between them. The specimen extracted from Sakhalin taimen (Parahucho perryi) was most similar to A. robusta. Thus, we here provide the first record of a new definitive host, P. perryi, for A. robusta and also molecular characteristics of the trematode specimens.

AZYGIID PARASITES OF NORTH AMERICAN ENDEMIC PLEUROCERIDS AND CENTRARCHIDS: REVISION OF LEUCERUTHRUS MARSHALL AND GILBERT, 1905 (DIGENEA: AZYGIIDAE), DESCRIPTION OF TWO NEW SPECIES, AND PHYLOGENETIC ANALYSIS

We revise monotypic LeuceruthrusMarshall and Gilbert, 1905 (Azygiidae Lühe, 1909) by emending its generic diagnosis, redescribing its type species (Leuceruthrus micropteriMarshall and Gilbert, 1905), reassigning 2 species (Leuceruthrus stephanocauda [Faust, 1921] n. comb., Leuceruthrus ocalana [Smith, 1935] n. comb.), describing 2 new congeners (Leuceruthrus ksepkai n. sp. and Leuceruthrus blaisei n. sp.), and providing a phylogenetic analysis based on the internal transcribed spacer 2 (ITS2). Leuceruthrus is unique by having oblique preovarian testes, a vitellarium that does not extend anteriad into the forebody, and a uterus that is intercecal and between the ovary and ventral sucker. We describe the cercaria of Leuceruthrus cf. stephanocauda from cercariae shed from Elimia cf. carinifera and Elimia cf. modesta from Big Canoe Creek, Alabama. Leuceruthrus ksepkai n. sp. is described from cercariae shed from rasp elimia, Elimia floridensis (Reeve, 1860) from Holmes Creek, Florida, and Elimia sp. 1 from the Chocktawhatchee River, Florida. It differs from its congeners by the combination of having broadly rounded furcae with slight marginal pigmentation in live cercariae, no spines on the tail stem, distinct anterior and posterior ridges that flank the tail stem portion accommodating the withdrawn distome, minute protuberances occupying the lateral margin of the tail stem for its entire length, and protuberances that encircle the anterior third of the posterior tail stem (immediately posterior to the tail stem portion containing the withdrawn distome). Leuceruthrus blaisei n. sp. infects Elimia sp. and is the only known congener having proportionally small furcae (>tail stem maximum width) with a nipple-like distal projection and numerous minute projections on the tail stem surface. Our phylogenetic analysis included all of our new sequences plus all publicly available ITS2 sequences for Leuceruthrus spp. and Proteromera spp., and supported the monophyly of Leuceruthrus. It recovered L. ksepkai and L. cf. ksepkai in a polytomy, and Leuceruthrus blaisei as monophyletic (identical sequences), with L. micropteri and L. cf. stephanocauda recovered as sister taxa. The present study comprises the first systematic treatment of Leuceruthrus in over a century, the first description of a new species of Leuceruthrus in 117 yr, and the first taxonomic characterization of a species of Leuceruthrus from the Mobile River Basin. It also increases the number of accepted congeners from 1 to 5 and provides new host records (E. cf. carinifera and E. floridensis) for Leuceruthrus spp.