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Characterization of the complete mitochondrial genome of Quasilineus sinicus Gibson, 1990 (Nemertea: Heteronemertea) and its phylogenetic implications

  • Chengde Medical University, Chengde, Hebei Province, China;


In this study, we sequenced and characterized the complete mitochondrial genome (mitogenome) of Quasilineus sinicus Gibson, 1990 (Heteronemertea, Nemertea) using Illumina sequencing technology. The circular mitogenome was 16,358 bp in length and comprised 22 transfer RNA genes, 13 protein-coding genes, and two ribosomal RNA genes. Its overall base composition included 20.82% A, 41.06% T, 26.68% G, and 11.44% C; in fact, the mitogenome had a high A + T content of 61.88%. Furthermore, our phylogenetic analysis demonstrated that Paleonemertea, Pilidiophora, and Hoplonemertea were monophyletic groups, and Q. sinicus was most closely related to Iwatanemertes piperata.
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Mitochondrial DNA Part B
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Characterization of the complete mitochondrial
genome of Quasilineus sinicus Gibson, 1990
(Nemertea: Heteronemertea) and its phylogenetic
Chun-Yang Shen, Wei Xue, Chong Pang, Asem Alireza, Xiaonan Mao, Jiahui
Han, Haonan Chen & Chunzheng Fu
To cite this article: Chun-Yang Shen, Wei Xue, Chong Pang, Asem Alireza, Xiaonan Mao, Jiahui
Han, Haonan Chen & Chunzheng Fu (2022) Characterization of the complete mitochondrial
genome of Quasilineus�sinicus Gibson, 1990 (Nemertea: Heteronemertea) and its phylogenetic
implications, Mitochondrial DNA Part B, 7:9, 1749-1751, DOI: 10.1080/23802359.2022.2126287
To link to this article:
© 2022 The Author(s). Published by Informa
UK Limited, trading as Taylor & Francis
Published online: 27 Sep 2022.
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Characterization of the complete mitochondrial genome of Quasilineus sinicus
Gibson, 1990 (Nemertea: Heteronemertea) and its phylogenetic implications
Chun-Yang Shen
, Wei Xue
, Chong Pang
, Asem Alireza
, Xiaonan Mao
, Jiahui Han
, Haonan Chen
Chunzheng Fu
Department of Biology, Chengde Medical University, Chengde, Hebei Province, China;
Department of Chemical Engineering, Hebei
Petroleum University of Technology, Chengde, Hebei Province, China;
Department of Pharmacology, Chengde Medical University, Chengde,
Hebei Province, China;
Hainan Key Laboratory for Conservation and Utilization of Tropical Marine Fishery Resources, Hainan Tropical Ocean
University, Sanya, Hainan Province, China;
Institute of Sericulture, Chengde Medical University, Chengde, Hebei Province, China
In this study, we sequenced and characterized the complete mitochondrial genome (mitogenome) of
Quasilineus sinicus Gibson, 1990 (Heteronemertea, Nemertea) using Illumina sequencing technology.
The circular mitogenome was 16,358 bp in length and comprised 22 transfer RNA genes, 13 protein-
coding genes, and two ribosomal RNA genes. Its overall base composition included 20.82% A, 41.06%
T, 26.68% G, and 11.44% C; in fact, the mitogenome had a high A þT content of 61.88%. Furthermore,
our phylogenetic analysis demonstrated that Paleonemertea, Pilidiophora, and Hoplonemertea were
monophyletic groups, and Q. sinicus was most closely related to Iwatanemertes piperata.
Received 18 April 2022
Accepted 14 September 2022
Quasilineus sinicus;
Nemertea; mitogenome;
phylogenetic analysis
The phylum Nemertea consists of approximately 1280 identi-
fied species of invertebrate animals known as nemerteans.
Most of these species are free-living animals in marine envi-
ronments with bodies that are only a few millimeters wide
(Kajihara et al. 2008). While the phylogenetic classification of
Nemertea has been unclear for a long time, it has recently
been classified into three classes: Palaeonemertea,
Pilidiophora, and Hoplonemertea (Strand et al. 2019).
Quasilineus sinicus Gibson, 1990 is a heteronemertean species
(Pilidiophora: Heteronemertea) that resides in intertidal zones
(Gibson 1990). It is characterized by three black and two
orange longitudinal stripes on the dorsal side of its body,
which is slender, cylindrical, or slightly flat and its body can
be 190 mm in length and 2 mm in width (Sun SC 1995). In
this study, we sequenced the complete mitochondrial gen-
ome (mitogenome) of Q. sinicus and investigated its taxo-
nomical and phylogenetic relationships within the class
Pilidiophora of the phylum Nemertea.
With regard to regulations of Natural Science Foundation
of Hebei Province (reference number: C2020406016), permis-
sion was obtained to collect samples from Diaolou Bay fol-
lowing the research program of Hebei Provincial Department
of Science and Technology. First, we collected the adult
specimens of Q. sinicus from Diaolou Bay (Lingao, Hainan
province, China; 195502000N, 1093104600 E). Their taxonomic
statuses were confirmed by Prof. Shi-Chun Sun from Ocean
University of China. Then the voucher specimens of Q. sinicus
were deposited in the Institute of Evolution & Marine
Biodiversity of Ocean University of China (Shi-Chun Sun,; voucher number, 20160414C1).
Subsequently, the genomic DNA was extracted from a single
specimen using the TIANamp Genomic DNA Kit (TIANGEN,
Beijing, China; NO. DP304). Next, a DNA library was prepared
using the NEB Next
DNA Library Prep Kit (NEB, USA)
and was sequenced on an Illumina NovaSeq 6000 platform.
Consequently, approximately 15 Gb of paired-end reads
(2 150 bp) were generated, and the mitogenome was
assembled de novo using GetOrganelle (Jin et al. 2020) with
approximately 300average coverage. The annotation of
transfer RNA (tRNA) genes was performed by tRNAscan-SE2.0
( and ARWEN (http:// Positions of the protein-coding
genes (PCGs) were determined using the online NCBI ORF
Finder server (, add-
itionally, these positions were manually validated by analyz-
ing the BLAST ( results
of related species. The ribosomal RNA (rRNA) genes were
annotated by aligning the rRNA gene sequences of species
related to Q. sinicus. The genomic DNA sequence of Q. sinicus
has been deposited in GenBank under the accession num-
ber MZ274345.
The complete circular mitogenome of Q. sinicus was
16,358 bp in length. Its overall nucleotide composition was
20.82% A, 41.06% T, 26.68% G, and 11.44% C. Similar to other
nemertean species, nucleotide composition of the Q. sinicus
mitogenome was strongly biased, as it had a total A þT con-
tent of 61.88%. In fact, the rRNA gene sequences had the
highest A þT content (66.90%), followed by the tRNA gene
CONTACT Chunzheng Fu Institute of Sericulture, Chengde Medical University, Chengde, 067000 Hebei Province, China
ß2022 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use,
distribution, and reproduction in any medium, provided the original work is properly cited.
2022, VOL. 7, NO. 9, 17491751
sequences (65.33%) and PCG sequences (59.99%). Typically,
the mitogenome contained 37 genes, including 22 tRNA
genes, 13 PCGs, and two rRNA genes. Only two genes (tRNA-
Pro and tRNA- Thr) were encoded on the light strain, whereas
the other 35 genes were located on the heavy strain.
Interestingly, all the PCG sequences had ATG as the start
codon; the only exception was the nad4 gene sequence that
had GTG as the start codon. Stop codons included TAG (cox1,
cox2,cox3,nad2, and nad4L), TAA (nad3,nad4,atp6,atp8,
and cytb), and non-complete codons T- (nad6,nad5, and
nad1) that are presumed to form a TAA codon upon post-
transcriptional polyadenylation (Boore JL 2001). Twenty-one
tRNA genes had a typical clover-leaf secondary structure,
whereas tRNA-Ser (AGA) lacked a DHU arm; this loss was
assumed to be an evolutionary loss (Haen et al. 2007). A
744 bp major non-coding region (mNCR) was located
between nad3 and tRNA-Ser (AGA) sequences. In addition,
there is a 5 bp motif (AAAAG) which is repeated for 5 times
in mNCR and this tandemly repeated sequences might play a
central role in regulating the transcription process within
genomes (Kolpakov et al. 2003). Furthermore, we identified
other 29 relatively short intergenic regions (ranging from 1
to 203 bp) that were scattered across the mitogenome.
In order to investigate the phylogenetic relationships
between Q. sinicus and other species in Nemertea, 20 mitoge-
nomes of nemertean were firstly used for phylogenetic
analyses, and Katharina tunicate and Phoronopsis harmeri were
set as outgroups (Boore and Brown 1994; Chen et al. 2009;
Podsiadlowski et al. 2009; Chen et al. 2011,2012; Xu et al.
2012; Sun WY et al. 2014; Sun WY and Sun 2014; Shen et al.
2015; Shen and Sun 2016; Sun WY et al. 2016; Jiang and Deng
2018; Redak and Halanych 2019; Nam and Rhee 2020).
Subsequently, a nucleotide concatenated dataset were gener-
ated using 13 PCGs and the best-fit model of nucleotide substi-
tution of this concatenated dataset was estimated to be
HKY þG using MrModeltest 2.2 (Nylander, 2004). Eventually,
the phylogenetic analysis of Nemertea was reconstructed by
MrBayes 3.2.2 (Miller et al. 2010). Our results revealed that
Palaeonemertea, Pilidiophora, and Hoplonemertea were mono-
phyletic groups (Figure 1). Notably, we discovered that Q. sini-
cus was closely related to Iwatanemertes piperata. As a kind of
macrobenthos, Q. sinicus usually crawls on the seafloor sedi-
ment, which can increase the exchange of chemical substances
at the sediment-water interface (Kanneworff and Christensen
1986). The present data will be useful for further phylogenetic
studies and population genetic studies of this species.
The authors are grateful to Shi-Chun Sun (Ocean University of China,
Qingdao, China) for the identification of samples. Our thanks to editage
( for English revision.
Figure 1. Phylogenetic tree shows evolutionary relationship among phylum Nemertea based on Bayesian Inference (BI) approach. Numbers behind major nodes
denote posterior probabilities. The GenBank accession numbers are indicated on the right side of species names. The newly sequenced Q.sinicus mitogenome is
highlighted using bold.
1750 C.-Y. SHEN ET AL.
Author contributions
In this study, Ch.Sh. and Ch.F. designed the research, analyzed the data
as well as conceived and wrote the article. Ch.Sh. collected the sample.
W.X. and A.A. modify the manuscript as well as polished the writing of
the paper. Ch.P., X.M., J.H. and H.Ch. collected the data from Genbank
used in this study. All authors read, discussed, and approved the final
version and all authors agree to be accountable for all aspects of
the work.
Disclosure statement
The authors report no conflicts of interest. The authors alone are respon-
sible for the content and writing of the manuscript.
This work was supported by Natural Science Foundation of Hebei
Province [Grant No. C2020406016]; Science and Technology Project of
Hebei Education Department [Grant No. QN2019093]; Introduced foreign
intelligence project of Hebei Province in 2021; Technology Innovation
Guidance Project-Science and Technology Work Conference of Hebei
Provincial Department of Science and Technology; Herbgenomics Team
of the Youth PI (principle investigator) Science and Technology
Innovation Team Project of Chengde Medical University; Research Project
of Chengde Medical University [Grant No. 202215] and Research Project
of Chengde Medical University [Grant No. 202008].
Data availability statement
The data that support the findings of this study are openly available in
GenBank of NCBI at, reference number
MZ274345. The associated BioProject, Bio-Sample and SRA numbers are
PRJNA799904, SAMN25211098 and SRS11750639, respectively.
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Here, we report the complete mitochondrial genome of the marine nemertean Cephalothrix species collected from the coastal region of South Korea. The mitochondrial genome of Cephalothrix sp. South Korea (SK) stain is 16,396 bp contains 13 protein-coding genes (PCGs) along with 22 transfer RNA (tRNA) genes, two ribosomal RNA (rRNA) genes, and an AT-rich noncoding region, arranged identically to those of Palaeonemertea. The nucleotide composition in the Cephalothrix sp. (SK) mitogenome is highly biased toward A and T as total AT content is 76.3% across the genome. A phylogenetic analysis of Nemertean species indicates that Cephalothrix sp. (SK) mitogenome shows close relationships to those of Palaeonemertea (Cephalothrix sp. and C. hongkongiensis collected from China).
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Between the years 1995 and 2007, 48 nominal genera and 128 nominal species of nemerteans were established worldwide. During this period, taxonomic changes such as synonymization, alteration of affiliation to higher taxa, and resurrection of formerly invalid names were made for 26 genera and 69 species. The nominal genera and species established between 1995 and 2007, as well as the taxonomic changes made at the genus and species level, are listed here with their original citations. The type depositories for the nominal species established since 1995 are also mentioned. In total, 285 genera and 1275 species are currently recognized as valid in the phylum Nemertea. Their distribution among higher taxa is as follows: Palaeonemertea (12 genera, 110 species), Pilidiophora (101, 450), Monostilifera (116, 570), Reptantia (15, 46), and Pelagica (40, 98), in addition to one species in a monotypic genus, the higher taxonomic affinities of which are uncertain. Two taxonomic and one nomenclatural changes are proposed herein: Sundbergia Gibson, 2002 and Tetramys Iwata, 1957 are tentatively transferred from the Palaeonemertea to the Pilidiophora, and Polydendrorhynchus Yin and Zeng, 1986 is substituted for Dendrorhynchus Yin and Zeng, 1985 to avoid homonymy with Dendrorhynchus Keilin, 1920 (Protozoa: Apicomplexa: Gregarinea); the latter results a new combination Polydendrorhynchus zhanjiangensis (Yin and Zeng, 1984).
The DNA sequence of the 15,532-base pair (bp) mitochondrial DNA (mtDNA) of the chiton Katharina tunicata has been determined. The 37 genes typical of metazoan mtDNA are present: 13 for protein subunits involved in oxidative phosphorylation, 2 for rRNAs and 22 for tRNAs. The gene arrangement resembles those of arthropods much more than that of another mollusc, the bivalve Mytilus edulis. Most genes abut directly or overlap, and abbreviated stop codons are inferred for four genes. Four junctions between adjacent pairs of protein genes lack intervening tRNA genes; however, at each of these junctions there is a sequence immediately adjacent to the start codon of the downstream gene that is capable of forming a stem-and-loop structure. Analysis of the tRNA gene sequences suggests that the D arm is unpaired in tRNA(ser)(AGN), which is typical of metazoan mtDNAs, and also in tRNA(ser)(UCN), a condition found previously only in nematode mtDNAs. There are two additional sequences in Katharina mtDNA that can be folded into structures resembling tRNAs; whether these are functional genes is unknown. All possible codons except the stop codons TAA and TAG are used in the protein-encoding genes, and Katharina mtDNA appears to use the same variation of the mitochondrial genetic code that is used in Drosophila and Mytilus. Translation initiates at the codons ATG, ATA and GTG. A + T richness appears to have affected codon usage patterns and, perhaps, the amino acid composition of the encoded proteins. A 142-bp non-coding region between tRNA(glu) and CO3 contains a 72-bp tract of alternating A and T.
Oxygen uptake was measured in the laboratory on sediment cores taken on 23 occasions with the Haps sampler (135 cm2) from a depth of 27 m in the middle of the Helsingør-Hälsingborg-Hven basin in the Øresund. The cores were incubated at temperature and salinity conditions of the sampling locality. Sedimentation of phytoplankton during the spring bloom (April) had no immediate effect on total benthic community respiration. Most of the input was stored and mineralized during summer and autumn. High temperature (10°C) was a prerequisite for a high mineralization rate. Oxygen consumption of macrofauna was calculated from biomass, which remained almost constant during the year. In spring macrofauna accounted for 40 % and in autumn for 30 % of total benthic community respiration, which was approximately 100 l O2/m2/year. This was equivalent to 44 g of organic carbon, of which 40 and 60 % respectively were consumed during first and second half of the year. Feeding and growth of macrofauna were high during spring and bioturbation instantaneously dispersed spring-bloom plant material homogeneously in the sediment. The result was that activity of macroinvertebrates lasted a short time and was low during summer and autumn when sediment consumed oxygen at a high rate primarily by bacterial respiration. Macrofaunal activity seemed not to be limited by low temperatures (3–4°C) in spring.
The complete mitochondrial genome (mitogenome) of Micrura bella was sequenced and analyzed. Being the largest mitogenome known to phylum Nemertea, the genome is 16 847 bp in length. It encodes 37 genes typical to metazoan mitogenomes and has the same gene arrangement with the other Heteronemertea mitogenomes sequenced to date. The genome has the maximal number of non-coding nucleotides (2037 bp at 25 sites) in Nemertea mitogenomes, among which two large non-coding regions were found (507 and 508 bp, respectively).
Abstract The complete mitochondrial genome (mitogenome) of Tetrastemma olgarum is sequenced. It is 14,580 bp in length and contains 37 genes typical for metazoan mitogenomes. The gene order is identical to that of the previously published Hoplonemertea mitogenomes. All genes are encoded on the heavy strand except for trnT and trnP. The coding strand is AT-rich, accounting for 69.2% of overall nucleotide composition.