Research Article
Research Article
Characterization and comparative analysis of the complete mitochondrial genome of Azygia hwangtsiyui Tsin, 1933 (Digenea), the first for a member of the family Azygiidae
expand article infoYuan-An Wu, Jin-Wei Gao, Xiao-Fei Cheng, Min Xie, Xi-Ping Yuan, Dong Liu, Rui Song
‡ Hunan Fisheries Science Institute, Changsha, China
Open Access


Azygia hwangtsiyui (Trematoda, Azygiidae), a neglected parasite of predatory fishes, is little-known in terms of its molecular epidemiology, population ecology and phylogenetic study. In the present study, the complete mitochondrial genome of A. hwangtsiyui was sequenced and characterized: it is a 13,973 bp circular DNA molecule and encodes 36 genes (12 protein-coding genes, 22 transfer RNA genes, two ribosomal RNA genes) as well as two non-coding regions. The A+T content of the A. hwangtsiyui mitogenome is 59.6% and displays a remarkable bias in nucleotide composition with a negative AT skew (–0.437) and a positive GC skew (0.408). Phylogenetic analysis based on concatenated amino acid sequences of twelve protein-coding genes reveals that A. hwangtsiyui is placed in a separate clade, suggesting that it has no close relationship with any other trematode family. This is the first characterization of the A. hwangtsiyui mitogenome, and the first reported mitogenome of the family Azygiidae. These novel datasets of the A. hwangtsiyui mt genome represent a meaningful resource for the development of mitochondrial markers for the identification, diagnostics, taxonomy, homology and phylogenetic relationships of trematodes.


gene arrangement, phylogenetic analysis, Trematoda


The genus Azygia Looss, 1899 is an endoparasitic helminth found in the stomach and intestine of freshwater feral carnivorous fish (Frolova and Shcherbina 1975). This genus includes several species complexes and its type species is Azygia lucii (Müller, 1776), which is a parasite of numerous, but especially esocid and percid, fishes in Europe. Many researchers have added to our knowledge of this cosmopolitan species. To date, species of Azygia are frequently reported from the esophagus, stomach, and intestine of a wide range of predatory fishes from Asia, Europe and North America, including China, Japan, India, Russia, Germany, and North America (Tubangui 1928; Tsin 1933; Moravec and Sey 1989; Marcogliese and Cone 1996; Besprozvannykh 2005; Jadhav et al. 2011; Pallewad et al. 2015; Womble et al. 2016; Nagasawa and Katahira 2017).

Azygia hwangtsiyui Tsin, 1933 is a member of the family Azygiidae Odhner, 1911 and is often overlooked; it is parasitic in the gastrointestinal tract of species of the family Channidae Fowler, 1934 but caused only slight clinical signs, including malnutrition and weight loss. In China, Azygia hwangtsiyui-infected freshwater predatory fishes have been described from Shandong, Heilongjiang, Jiangsu, Fujian, Sichuan and Hunan Provinces (Tsin 1933; Zmejev 1936; Ma 1958; Tang and Tang 1964; Kiang 1965; Chen 1973; Wang 1985; Cheng 2011). It has a mainly inland distribution and utilizes freshwater snail species (e.g. Vivipara quadrata (Benson, 1842)) as intermediate hosts (Tang and Tang 1964) and develops into adults in the gastrointestinal tract of predatory fish species such as Ophiocephalus argus Cantor, 1842 and Channa asiatica (Linnaeus, 1758) (Tsin 1933; Besprozvannykh 2005).

Morphology is the most commonly used method for species identification and differentiation of metazoans and is widely adopted globally by parasitologists and taxonomists. A huge disadvantage of using morphological criteria, however, is that it is difficult to identify and distinguish closely related and cryptic species. Although the family Azygiidae was erected more than a century ago, its situation, and that of several species of Azygia, is still controversial and uncertain. Manter (1926) pointed out that Azygia is the only genus in the family then presenting systematic confusion: Azygia longa (Leidy, 1851) in North America may be a synonym of A. lucii in Europe (Manter 1926), and Van Cleave and Mueller (1934) reported that Azygia acuminata Goldberger, 1911 and A. longa should be considered conspecific. Nevertheless, due to the discovery of some life histories of members of Azygia, A. lucii and A. longa have been recognized as two distinct species (Szidat 1932; Sillman 1953; Sillman 1962).

Mitochondrial (mt) genome and nuclear ribosomal DNA sequences are effective molecular tools for taxonomic identification, phylogeny and biogeographical research (Bernt et al. 2013; Le et al. 2019). However, only a partial cytochrome oxidase subunit 1 protein sequence (AIY67834) of Proterometra macrostoma Horsfall, 1933 (Azygiidae) is currently available in GenBank. None of the mitochondrial genome data have been sequenced for a member of the family Azygiidae. Therefore, we determined the complete mitochondrial genome sequence of A. hwangtsiyui as a basis for the future definition of strain- and species-specific markers, and for assessing mitogenomics in resolving the interrelationships of trematodes.

Materials and methods

Sampling and DNA extraction

The specimens of flatworms were isolated from the stomach of their definitive host, in this case snakehead fish (Ophiocephalus argus (Cantor, 1842)) obtained from east Dongting Lake in Yueyang, Hunan province, China (29°22'N, 113°06'E). Azygia hwangtsiyui was morphologically identified according to the original and other descriptions (Tsin 1933; Tang and Tang 1964; Zhang et al. 1999; Besprozvannykh 2005), using a stereomicroscope and a light microscope. Furthermore, single samples were confirmed molecularly as A. hwangtsiyui based on sequencing of 1370 bp 28S rDNA sequence. The parasites were completely washed in water, preserved in 99% ethanol, and stored at 4 °C until genomic DNA extraction. Total genomic DNA extraction was performed from an intact specimen with the TIANamp Micro DNA Kit (Tiangen Biotech, Beijing, China), according to the manufacturer’s instructions.

DNA amplification and sequencing

According to conserved regions of mitochondrial genes in other available digenea mitogenomes, six partial gene fragments for cytb, nad4, nad1, 16S, 12S and cox2 were amplified using six generic primers sets HWF1/HWR1 (for cytb), HWF3/HWR3 (for nad4), HWF5/HWR5 (for nad1), HWF7/HWR7 (for 16S), HWF9/HWR9 (for 12S), and HWF11/HWR11 (for cox2), respectively. On the basis of these obtained nucleotide sequences, A. hwangtsiyui-specific primers were designed for amplification and sequencing of the remaining mitogenome (Suppl. material 1: Table S1). All primers were designed to produce amplicons with overlaps of approximately 100 bp. PCR reactions were performed in a 50 µl reaction solution with the ingredient of 18.5 µl ddH2O, 25 µl 2×PCR buffer (Mg2+, dNTP plus, Takara, Dalian, China), 1.5 µl of each primer (0.2–1.0 μM), 1 µl EX Taq polymerase (250U, Takara), and 2.5 µl DNA template. PCR amplification was compliant to the following amplification protocol: initial denaturation at 98 °C for 2 min, followed by 40 cycles 10 s at 98 °C, 15 s at 50 °C, 68 °C for 1 min/kb, and 10 min at 68 °C for a final extension. The amplified PCR products were purified with TIANgel Purification Kit (Tiangen Biotech, Beijing, China), and sequenced bidirectionally at Sangon Biotech (Shanghai) Co., Ltd. (Shanghai, China) based on the primer walking method using several specific primers (Suppl. material 1: Table S1).

Mitogenome annotation and analysis

According to sequence chromatograms, all raw fragments were quality-proofed using CHROMAS ( to remove ambiguity codes and low-quality bases. Whenever the quality was sub-optimal, sequencing was repeated until the amplicon is the consensus sequence. Before manual assembly of the entire mitochondrial genomic sequence, identification of all amplicons was performed by BLASTN check (Altschul et al. 1990). The mt genome of A. hwangtsiyui was aligned against the mt genome sequences of other promulgated digenean mitogenomes utilizing multiple sequence alignment software MAFFT version 7.149 (Katoh and Standley 2013) to identify genetic boundary. Protein-coding genes (PCGs) were predicted with Open Reading Frame Finder ( adopting echinoderm and flatworm mitochondrial codes, and examining the nucleotide alignment against the reference mtDNA in trematode Dicrocoelium chinense Tang et Tang, 1978 (NC_025279.1). Whole tRNAs were inferred with the detection results of ARWEN (Laslett and Canback 2008) and MITOS web server (Bernt et al. 2013). Two rRNA (rrnL and rrnS) were founding by comparison with those of published fluke mitogenomes. Codon usage and relative synonymous codon usage (RSCU) for 12 PCGs of A. hwangtsiyui were computed by PHYLOSUITE (Zhang et al. 2020), and its operation results were imported into GGPLOT2 program (Wickham 2016) to make figures of the RSCU. Tandem repeats in the non-coding regions were determined with Tandem Repeats Finder software version 4.09 (Benson 1999), and the prediction of their secondary structures were performed by the MFOLD web server (Zuker 2003). The annular diagram of A. hwangtsiyui mitogenome was plotted with mitochondrial genome data visualization tool MTVIZ (

Phylogenetic analysis

For phylogenetic analyses, we utilized translated and concatenated amino acid sequences of twelve protein-coding genes for 49 Platyhelminthes including A. hwangtsiyui mitogenome determined in this study. Two tapeworm species, Cloacotaenia megalops (Nitzsch in Creplin, 1829) (NC_032295.1) and Dibothriocephalus latus (Linnaeus, 1758) (NC_008945.1) were included as outgroup taxa representing two different families. Species information including systematic positions and GenBank accession numbers is provided in Suppl. material 2: Table S2. The PHYLOSUITE program was used to extract twelve PCGs from the GenBank files, export fasta files with translated amino acid datasets, and align datasets in bulk using integrated applet MAFFT with normal-alignment mode. Phylogenetic analyses were performed using Bayesian Inference (BI) and Maximum Likelihood (ML) methods. Assessment of the best-fit evolutionary model for dataset was conducted via ModelGenerator v0.8527 (Keane et al. 2006). BI in MrBayes version 3.2.6 (Ronquist et al. 2012) was carried out under the MtRev matrix of amino acid substitution, and was analyzed with 1 × 107 metropolis-coupled Monte Carlo Markov Chain (MCMC) generations. Two independent runs with four simultaneous MCMC chains (one cold and three heated chains) were conducted for 1 × 107 million generations, sampling every 10,000 generations and discarding the initial 25% generations as burn-in. ML analysis in PHYLOSUITE was performed using MtART+I+G matrix with 1000 bootstrap replicates.

Results and discussion

General traits of the Azygia hwangtsiyui mitogenome

The entire A. hwangtsiyui mtDNA is 13,973 bp in length (GenBank accession number: MN844889) and comprised of 12 protein-coding genes (cox1-3, nad1-6, nad4L, cytb, and atp6), 22 tRNA genes, two rRNA genes (rrnL and rrnS), and two non-coding regions. The 12 protein-coding gene order arrangement is cox3-cytb-nad4L-nad4-atp6-nad2-nad1-nad3-cox1-cox2-nad6-nad5 (Fig. 1), which is identical to those of Clinostomum complanatum (Rudolphi, 1814), Echinostoma hortense Asada, 1926, and some species of the Fasciolidae (Fasciola hepatica Linneuus, 1758, Fasciola gigantica Cobbold, 1856, and Fasciola sp. GHL-2014) (Liu et al. 2014a; Chen et al. 2016; Liu et al. 2016); the gene atp8 is similarly missing, as usual in trematode species. All genes are transcribed in the anticlockwise direction and encoded by H strand (Table 1), which is in accordance with other digeneans. The mt genome of A. hwangtsiyui has 22 intergenic spacers ranging from 1 to 15 bp and contains two overlapping nucleotides ranging from 1 to 40 bp (Table 1). Noteworthily, a 40 bp overlap between the nad4 and nad4L genes exists in the A. hwangtsiyui mitogenome, which is consistent with most helminths such as Eurytrema pancreaticum Janson, 1889 (Chang et al. 2016), Hypoderaeum conoideum (Bloch, 1782) (Yang et al. 2015), but shorter than that of Schistosoma mekongi Voge, Bruckner & Bruce, 1978 (64 bp; Littlewood et al. 2006). The nucleotide contents of T, C, A, G, in A. hwangtsiyui mitogenome are 42.8%, 12.0%, 16.8%, and 28.5%, respectively (Table 2). The whole A+T content of the mitogenome is 59.6%, which was markedly biased toward T over A (AT skew: –0.437), and G over C (GC skew: 0.408).

Table 1.

The organization of the mitochondrial genome of Azygia hwangtsiyui.

Gene Position Size Intergenic nucleotides Codon Anti-codon Strand
From To Start Stop
cox3 1 660 660 ATG TAG H
trnH 666 729 64 +5 GTG H
cytb 732 1841 1110 +2 ATG TAG H
nad4L 1848 2108 261 +6 ATG TAG H
nad4 2069 3340 1272 –40 ATG TAG H
trnQ 3345 3409 65 +4 TTG H
trnF 3423 3488 66 +13 GAA H
trnM 3490 3555 66 +1 CAT H
atp6 3556 4068 513 ATG TAG H
nad2 4072 4932 861 +3 GTG TAG H
trnV 4946 5009 64 +13 TAC H
trnA 5013 5076 64 +3 TGC H
trnD 5081 5146 66 +4 GTC H
nad1 5149 6054 906 +2 GTG TAG H
trnN 6070 6134 65 +15 GTT H
trnP 6148 6212 65 +13 TGG H
trnI 6216 6279 64 +3 GAT H
trnK 6280 6348 69 CTT H
nad3 6349 6708 360 ATG TAA H
trnS1 6712 6770 59 +3 GCT H
trnW 6781 6842 62 +10 TCA H
cox1 6843 8396 1554 TTG TAG H
trnT 8410 8474 65 +13 TGT H
rrnL 8475 9449 975 H
trnC 9450 9506 57 GCA H
rrnS 9507 10246 740 H
cox2 10247 10828 582 GTG TAA H
nad6 10834 11277 444 +5 GTG TAG H
trnY 11284 11352 69 +6 GTA H
trnL1 11352 11416 65 –1 TAG H
trnS2 11421 11490 70 +4 TGA H
trnL2 11491 11555 65 TAA H
trnR 11558 11617 60 +2 TCG H
nad5 11626 13225 1600 +8 GTG T H
trnE 13226 13288 63 TTC H
trnG 13604 13669 66 TCC H
Table 2.

Nucleotide contents of genes and the non–coding region within the mitochondrial genome of Azygia hwangtsiyui.

Regions Size (bp) T C A G AT (%) GC (%) AT skew GC skew
atp6 513 50.5 11.3 12.9 25.3 63.4 36.6 –0.594 0.383
cox1 1554 44.0 13.0 15.9 27.1 59.9 40.1 –0.469 0.352
cox2 582 39.7 13.1 18.0 29.2 57.7 42.3 –0.375 0.382
cox3 660 44.8 11.4 15.9 27.9 60.7 39.3 –0.476 0.421
cytb 1110 44.4 13.5 15.8 26.3 60.2 39.8 –0.476 0.321
nad1 906 44.0 10.0 16.3 29.6 60.3 39.6 –0.459 0.493
nad2 861 46.2 11.3 11.8 30.7 58.0 42.0 –0.592 0.463
nad3 360 45.8 8.1 14.2 31.9 60.0 40.0 –0.528 0.597
nad4 1272 45.7 12.8 12.3 29.2 58.0 42.0 –0.577 0.391
nad4L 264 47.0 8.0 17.8 27.3 64.8 35.3 –0.450 0.548
nad5 1600 46.4 9.5 14.1 30.0 60.5 39.5 –0.535 0.519
nad6 444 45.9 11.9 14.2 27.9 60.1 39.8 –0.528 0.401
rrnL 975 37.4 14.1 22.5 26.1 59.9 40.2 –0.250 0.299
rrnS 740 36.6 14.5 21.6 27.3 58.2 41.8 –0.258 0.307
tRNAs 1349 35.3 14.5 21.7 28.5 57.0 43.0 –0.238 0.328
rRNAs 1715 37.1 14.2 22.1 26.6 59.2 40.8 –0.253 0.303
PCGs 10126 45.2 11.5 14.7 28.6 59.9 40.1 –0.509 0.425
Genome 13973 42.8 12.0 16.8 28.5 59.6 40.5 –0.437 0.408
Figure 1. 

An annular diagram of the Azygia hwangtsiyui mitochondrial genome.

Protein-coding genes and non-coding regions

A total of 3364 amino acids was encoded by the A. hwangtsiyui mtDNA. The full scale of 12 concatenated protein-coding genes was 10126 bp, composed of 45.2% T, 11.5% C, 14.7% A, and 28.6% G. Average A+T content of concatenated 12 protein-coding genes was 59.9%, varying from 57.7% (cox2) to 64.8% (nad4L) (Table 2 and Suppl. material 2: Table S2). All 12 protein-coding genes of A. hwangtsiyui mt genome have a lower A+T percentage than those of Trichobilharzia szidati Neuhaus, 1952, Calicophoron microbothrioides Price & McIntosh, 1944, and some members of the Schistosomatidae Poche, 1907, but possess a higher A+T percentage than those of Metagonimus yokogawai Katsurada, 1912, and Paragonimus westermani Kerbert, 1878 (Suppl. material 3: Table S3) (Lee et al. 1987; Littlewood et al. 2006; Biswal et al. 2014; Semyenova et al. 2017; Oey et al. 2019). There is an obvious bias towards T over A (AT skew = –0.509), and G over C (GC skew = 0.425), and the coding strand is enriched with T and poor with A and especially C. For A. hwangtsiyui, the length of protein-coding genes was followed in the order: nad5 (1600 bp) > cox1 (1554 bp) > nad4 (1272 bp) > cytb (1110 bp) > nad1 (906 bp) > nad2 (861 bp) > cox3 (660 bp) > cox2 (582 bp) > atp6 (513 bp) > nad6 (444 bp) > nad3 (360 bp) > nad4L (264 bp). There are two non-coding regions (NCR1 and NCR2) in A. hwangtsiyui mitogenome, while the mt genome of Paragonimus heterotremus Chen et Hsia (1964), C. complanatum, Fascioloides magna (Bassi, 1875), and T. szidati have a single non-coding region (Chen et al. 2016; Ma et al. 2016; Semyenova et al. 2017; Qian et al. 2018). NCR1 and NCR2 of the A. hwangtsiyui mitogenome is partitioned into two parts by trnG, and accompanied by 70.5% and 57.6% A+T content, respectively. NCR1 and NCR2 have similar chemical base counts, 315 bp and 317 bp in size, respectively. While the NCR1 lacks distinguishing features and any tandem repeats, the NCR2 contains two typical tandem repeats, and each of tandem repeats sequence (120 bp) forms a hairpin-like secondary structure including a whole set of stems and loops (Suppl. material 4: Figure S1). Although tandem repeats are a segment of function-deficiency mitochondrial genome sequences, its hairpin-like secondary structures are widely perceived as regulating the replication and transcription of mitochondrial genome.

Codon usage, transfer RNAs, and ribosomal RNAs

For the A. hwangtsiyui mitogenome, codon ends in G or T were more continual than those ending in A or C. The most frequently used start codon in protein-coding genes was ATG (for six PCGs), secondly was GTG (for five PCGs), which resembles that of the most frequent extrapolated start codons for mitogenome protein-encoding genes of digenean species (Chen et al. 2016). The least-used start codon was TTG (only one PCGs). Likewise, the most-used terminal codon was TAG (for nine PCGs), followed by TAA (for two PCGs). Only one of 12 protein-coding sequence (nad5) was terminated with abbreviated T stop codon (Table 1). Although incomplete stop codons (T or TA) frequently occur in cestodes and nematodes, they were rarely presented in flukes other than D. chinensis, Dicrocoelium dendriticum (Rudolphi, 1819), and Postharmostomum commutatum (Dietz, 1858) (Liu et al. 2014b; Fu et al. 2019). The codon UUU (Phe, 10.17%), UUG (Leu, 8.17%), and GUU (Val, 7.19%) were the most frequently occurring codons in protein-coding genes. Leucine, valine, and phenylalanine are the most-used amino acids, with frequency of 15.96%, 13.38%, and 11.09%, respectively. The least-used codons were CGA (Arg, 0.06%) and GAC (Asp, 0.15%), and the least frequent utilized amino acid was glutamine (1.01%) (Suppl. material 5: Figure S2). As most of digenea mitogenome sequences, the mitogenome of A. hwangtsiyui possessed 22 commonly found tRNAs, with the exception of that of P. westermani Korean isolate (23 tRNAs), and P. westermani Indian isolate (24 tRNAs) (Biswal et al. 2014). In A. hwangtsiyui, tRNA-Gly (trnG) is located between NCR1 and NCR2 (Fig. 1). The size of ribosomal RNA genes (rrnL and rrnS) in mitochondrial DNA of A. hwangtsiyui are 975 bp and 740 bp, respectively (Table 2). The upstream and downstream of rrnL and rrnS are cascaded with trnT and cox2 genes, respectively, and are detached from each other by trnC, as in all reported platyhelminths to date (Littlewood et al. 2006, Le et al. 2016).

Gene arrangement

Comparative analysis of gene arrangement among 47 selected digenean taxa, two gene blocks (cox1-trnT-rrnL-trnC-rrnS-cox2-nad6 and cytb-nad4L-nad4-trnQ) are shared by all selected taxa (Fig. 2). Disregarding P. heterotremus and members of the family Schistosomatidae and Fasciolidae Raillet, 1895, the gene order of the remaining digenea taxa is virtually identical with the exception of the translocation of trnE and trnG among the remaining members of selected digenea representatives in family level. Intriguingly, there is the translocation of trnE and trnG within different species of family Fasciolidae. The translocations of three tRNAs (trnS1, trnS2 and trnS) can be discovered even between taxa of the same subgroup. Gene order of the Brachycladium goliath (Van Beneden, 1858) mt genome (the only representative of family Brachycladiidae Faust, 1929) is nearly same as that of P. westermani (Troglotrematidae Ward, 1918) except for the relocations of trnY between trnG and cox3, and trnE to the position between trnN and trnP. The groups of Schistosomatidae show a massive gene reorganization of protein-coding genes and tRNAs compared with other sequenced digenea mitogenome, which is in accord with previous finding reported by Littlewood et al. (2006).

Figure 2. 

Phylogenetic relationships and gene arrangement of Azygia hwangtsiyui with other selected digeneas based on translated mitochondrial proteins. The concatenated amino-acid sequence datasets of the 12 protein-coding genes were analyzed by Bayesian Inference (BI) and Maximum Likelihood (ML), utilizing Cloacotaenia megalops (NC_032295.1) and Dibothriocephalus latus (NC_008945.1) as the outgroups. Both ML and BI analyses constructed identical tree topologies.

Mitogenome-derived phylogeny

To assess phylogenetic relationships among available flatworms, we utilized concatenated amino acid sequence dataset representing 12 protein-coding genes of A. hwangtsiyui, 46 other digenean representatives, and two tapeworm species (C. megalops and D. latus) for analyzing molecular-based phylogeny. In this study, the topological structure is divided into two large clades: one consists of seven members of the family Schistosomatidae; and the other clade comprises 40 members from 16 families including the family Azygiidae (A. hwangtsiyui) (Fig. 2). The topological structure shows that A. hwangtsiyui (Azygiidae) is identified as the most basal lineage of the Digenea, but separated from C. complanatum (Clinostomidae Lühe, 1901), and Cyathocotyle prussica Mühling, 1896 (Cyathocotylidae Poche, 1926). Phylogenetic analyses of all complete digenea mtDNAs confirmed taxonomic and previous phylogenetic assessments (Olson et al. 2003; Kostadinova and PéRez-del-Olmo 2014; Fu et al. 2019). The intricate structure and varying content of the family Azygiidae still awaits investigation of relationships based on a much wider taxon sampling and more mitogenome datasets.


This work was supported by the Earmarked Fund for China Agriculture Research System (CARS-45) and Important Research Project of Hunan Provincial Science and Technology Department (2016NK2176).


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Supplementary materials

Supplementary material 1 

Table S1

Yuan-An Wu, Jin-Wei Gao, Xiao-Fei Cheng, Min Xie, Xi-Ping Yuan, Dong Liu, Rui Song

Data type: molecular data

Explanation note: Primers for amplification and sequencing mitochondrial genome of Azygia hwangtsiyui.

This dataset is made available under the Open Database License ( The Open Database License (ODbL) is a license agreement intended to allow users to freely share, modify, and use this Dataset while maintaining this same freedom for others, provided that the original source and author(s) are credited.
Download file (35.50 kb)
Supplementary material 2 

Table S2

Yuan-An Wu, Jin-Wei Gao, Xiao-Fei Cheng, Min Xie, Xi-Ping Yuan, Dong Liu, Rui Song

Data type: molecular data

Explanation note: Information of the Digenea and the outgroups for which complete mitogenomes are available in GenBank.

This dataset is made available under the Open Database License ( The Open Database License (ODbL) is a license agreement intended to allow users to freely share, modify, and use this Dataset while maintaining this same freedom for others, provided that the original source and author(s) are credited.
Download file (55.00 kb)
Supplementary material 3 

Table S3

Yuan-An Wu, Jin-Wei Gao, Xiao-Fei Cheng, Min Xie, Xi-Ping Yuan, Dong Liu, Rui Song

Data type: molecular data

Explanation note: A+T content (%) for 12 protein-coding genes in the available 49 Platyhelminthes mitogenomes.

This dataset is made available under the Open Database License ( The Open Database License (ODbL) is a license agreement intended to allow users to freely share, modify, and use this Dataset while maintaining this same freedom for others, provided that the original source and author(s) are credited.
Download file (40.00 kb)
Supplementary material 4 

Figure S1

Yuan-An Wu, Jin-Wei Gao, Xiao-Fei Cheng, Min Xie, Xi-Ping Yuan, Dong Liu, Rui Song

Data type: molecular data

Explanation note: Secondary structure of tandem repeats in non-coding region 2 (NCR2) of Azygia hwangtsiyui mitochondrial genome.

This dataset is made available under the Open Database License ( The Open Database License (ODbL) is a license agreement intended to allow users to freely share, modify, and use this Dataset while maintaining this same freedom for others, provided that the original source and author(s) are credited.
Download file (1.48 MB)
Supplementary material 5 

Figure S2

Yuan-An Wu, Jin-Wei Gao, Xiao-Fei Cheng, Min Xie, Xi-Ping Yuan, Dong Liu, Rui Song

Data type: molecular data

Explanation note: Relative synonymous codon usage (RSCU) of Azygia hwangtsiyui mitochondrial genome.

This dataset is made available under the Open Database License ( The Open Database License (ODbL) is a license agreement intended to allow users to freely share, modify, and use this Dataset while maintaining this same freedom for others, provided that the original source and author(s) are credited.
Download file (2.67 MB)
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