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Girardia tigrina, a freshwater planarian species native to America and introduced to other continents, has been usually used as model organism in many research fields of biology. In this study, we determined the complete mitochondrial genome of G. tigrina using next-generation sequencing (NGS). The complete mitogenome was 15,938 bp in length, with 36 genes, including 12 protein-coding genes, 2 ribosomal RNAs and 22 transfer RNAs, and ATP8 was absent in the mitogenome of G. tigrina as in the mitogenomes of some other flatworms. The maximum-likelihood phylogenetic tree suggested that G. tigrina was closely related to genus Dugesia in the clade of Tricladida.

Our previous study based on the transcriptome profiling indicated that a fragment of α-crystallin type heat shock protein (α-Hsp) gene was one of the numerous cDNA sequences expressed differentially at various stages of head regeneration in Hydra vulgaris. To further investigate the role that which α-Hsp plays during hydra regeneration, a full-length cDNA of α-Hsp gene of H. vulgaris was isolated by the rapid amplification of cDNA ends (RACE) technique. The full-length cDNA of α-Hsp gene was 1156 bp, containing a 765 bp open-reading frame (ORF), which encodes a polypeptide of 254 amino acid residues with a molecular weight of 29.27 kDa. Further, the ORF was subcloned into the plasmid pET-42a(+), and the recombinant plasmid pET-42a(+)-α- Hsp was transformed to Escherichia coli BL21(DE3), then the fusion protein GST-α-Hsp was expressed mainly in the form of a soluble molecule after induction by isopropyl-β-d-thiogalactopyranoside. In addition, BALB/Cmice were immunized with the fusion protein to prepare the polyclonal antiserum which was used as the primary antibody for whole-mount immunohistochemical assay. The results from the immunohistochemical assay showed that α-Hsp had expressedmainly at the wound site and nearby area of hydra after decapitation operation, and both quantitative real-time polymerase chain reaction (qPCR) analysis and immunohistochemical assay revealed that the expression level of α-Hsp increased gradually during the early period of hydra regeneration, then reached a peak at 24 h after decapitation operation, while decreased during the late regeneration period. Moreover, it indicated an important role of α-Hsp gene in hydra head regeneration that RNA interference (RNAi)-mediated α-Hsp silencing led to the obvious delay of the regeneration of head structures in H. vulgaris. In conclusion, our results gave the hint that α-Hsp could be related to wound healing and tissue remodelling at early regeneration stages, and may lay the foundation for further studies about the physiological function and role of α-Hsp during hydra regeneration.

The complete mitochondrial genome of Oxyopes sertatus is a circular molecule of 14,442 bp in length, containing 13 protein-coding genes, 2 ribosomal RNAs, 22 transfer RNAs, and a control region. The A + T content of the overall base composition of H-strand is 75.9% (T: 42.9%; C: 8.2%; A: 33.0%; G: 15.9%). COII, COIII and ND4 genes begin with TTG as start codon; ATP6, COI, ND1 and ND5 genes begin with ATA as start codon, ATP8, Cyt b, ND2 and ND3 genes begin with ATT as start codon, ND6 gene begins with GTG as start codon, while ND4L gene start with a typical ATG initiation codon. ND2 gene is terminated with TAG as stop codon, Cyt b and ND5 end with TA, COI, ND1 and ND4L end with T, ATP6, ATP8, COII, COIII, ND3, ND4 and ND6 end with TAA.

The complete mitochondrial genome of Selenops bursarius is a circular molecule of 14,272 bp in length, containing 13 protein-coding genes, 2 ribosomal RNAs, 22 transfer RNAs and a control region. The A + T content of the overall base composition of H-strand is 74.4% (T: 41.8%; C: 8.7%; A: 32.6%; G: 16.9%). COI gene begins with TTA as start codon; COII gene begins with GTG as start codon; ATP6 and ATP8 genes begin with ATA as start codon; COIII and ND4 genes begin with TTG as start codon; ND1 and ND5 genes begin with ATC as start codon, while other five protein-coding genes start with ATT. ATP6, ATP8, COII, COIII, ND2, ND3, ND4 and ND5 genes are terminated with TAA as stop codon, ND1 ends with TAG, COI ends with TG, Cyt b, ND4L and ND6 end with T.

Juema pig is a kind of rare and special pig which is well adapted to high altitude, cold climate and harsh natural environment. The complete mitochondrial genome of Juema pig Sus scrofa is a circular molecule of 16 532 bp in length, containing 13 protein-coding genes, two ribosomal RNAs, 22 transfer RNAs, and a control region. The A + T content of the overall base composition of H-strand is 60.7% (T: 26.2%; C: 26.0%; A: 34.5%; G: 13.3%). ND4L gene begins with GTG as start codon, ND2, ND3, and ND5 genes begin with ATA as a start codon, and other nine protein-coding genes start with ATG. Cyt b gene is terminated with AGA as stop codon, ND1 and ND2 genes are terminated with TAG as stop codon, COII, COIII, ND3, and ND4 end with T, while ATP6, ATP8, COI, ND4L, ND5, and ND6 end with TAA. In addition, the phylogenetic relationships from neighbor-joining analyses based on the 13 concatenated PCGs indicated (Tylopoda (Suina (Ruminantia (Hippopotamidae, Cetacea)))).

The stretch spider Tetragnatha maxillosa (Araneae: Tetragnathidae) is found all over the world. In the present study, we investigated the complete mitochondrial genome of T. maxillosa and the mitogenome is a circular molecule of 14 414 bp in length, consists of 13 protein-coding genes, two ribosomal RNAs, 22 transfer RNAs, and a control region. The A + T content of the overall base composition of H-strand is 74.5% (T: 40.4%; C: 9.6%; A: 34.1%; G: 15.9%). COI gene begins with TTT as start codon, COII and COIII genes begin with TTG as start codon, ATP8, Cyt b, ND2, and ND4L genes begin with ATT as start codon, and other six protein-coding genes start with ATA. ATP6, ATP8, COI, COIII, ND1, ND3, and ND6 genes are terminated with TAA as stop codon, Cyt b, ND2, ND4, ND4L, and ND5 end with T, and COII ends with TAG. In addition, the phylogenetic relationships from neighbor-joining analyses based on the 13 concatenated PCGs indicated (Tetragnatha (Nephila (Argiope (Araneus, Neoscona)))).

The complete mitochondrial genome of Hydra vulgaris (Hydroida: Hydridae) is composed of two linear DNA molecules. The mitochondrial DNA (mtDNA) molecule 1 is 8010 bp long and contains six protein-coding genes, large subunit rRNA, methionine and tryptophan tRNAs, two pseudogenes consisting respectively of a partial copy of COI, and terminal sequences at two ends of the linear mtDNA, while the mtDNA molecule 2 is 7576 bp long and contains seven protein-coding genes, small subunit rRNA, methionine tRNA, a pseudogene consisting of a partial copy of COI and terminal sequences at two ends of the linear mtDNA. COI gene begins with GTG as start codon, whereas other 12 protein-coding genes start with a typical ATG initiation codon. In addition, all protein-coding genes are terminated with TAA as stop codon.

The complete mitochondrial genome of Chinese green hydra, Hydra sinensis (Hydroida: Hydridae) is a linear molecule of 16,189 bp in length, containing 13 protein-coding genes, small and large subunit ribosomal RNAs, methionine and tryptophan transfer RNAs, a pseudogene consisting of a partial copy of COI and terminal sequences at two ends of the linear mitochondrial DNA. The A + T content of the overall base composition of H-strand is 77.2% (T: 41.7%; C: 10.9%; A: 35.5%; and G: 11.9%). COI and ND1 genes begin with GTG as start codon, while other 11 protein-coding genes start with a typical ATG initiation codon. COII, ATP8, ATP6, COIII, ND5, ND6, ND3, ND1, ND4 and COI genes are terminated with TAA as stop codon, ND4L ends with TAG, ND2 ends with TA and Cyt b ends with T.

The complete mitochondrial genome of Sinanodonta woodiana is a circular molecule of 16256 bp in length, containing 14 protein-coding genes, 2 ribosomal RNAs, 22 transfer RNAs, and 2 control regions. The A + T content of the overall base composition of H-strand is 65.9% (T: 28.0%; C: 22.3%; A: 37.9%; G: 11.8%). F ORF (Female-specific open reading frame) begins with ATA, Cyt b begins with ATC, ATP6, ATP8, COII, COIII, ND1, ND2, ND3 and ND5 begin with ATG, ND4L begins with GTG, COI begins with TTG, and other two protein-coding genes begin with ATT as start codon. COII, COIII, F ORF, ND1, ND3, ND5 and ND6 genes are terminated with TAA as stop codon, ATP6, ATP8, COI, Cyt b, ND4 and ND4L end with TAG, and ND2 gene ends with T.

The complete mitochondrial genome of Pardosa laura is a circular molecule of 14,513 bp in length, containing 13 protein-coding genes, 2 ribosomal RNAs, 22 transfer RNAs, and a control region. The A + T content of the overall base composition of H-strand is 77.4% (T: 42.9%; C: 8.1%; A: 34.5%; G: 14.5%). ATP6, COII and COIII genes begin with TTG as start codon; ND4 and ND6 genes begin with ATA as start codon, while other eight protein-coding genes start with ATT. COII, COIII, ND2 and ND6 genes are terminated with TAG as stop codon, COI and ND4L end with T, ND4 ends with TA, ATP6, ATP8, Cyt b, ND1, ND3and ND5 end with TAA.

The complete mitochondrial genome of Argiope amoena is a circular molecule of 14,121 bp in length, contains 13 protein-coding genes, 2 ribosomal RNAs, 21 transfer RNAs genes and a control region. The A + T content of the overall base composition of H-strand is 72.1% (T: 38.2%; C: 10.6%; A: 33.9%; G: 17.3%). ND1, ND4, ND6 and ATP6 begin with ATA as start codon, ND4L begins with ATG, ATP8, Cyt b, ND2 and ND3 genes begin with ATT, and the other two protein-coding genes begin with TTG. ATP6, ATP8, COI, COII, COIII, Cyt b, ND1, ND2, ND3, ND4L and ND5 genes are terminated with TAA as stop codon, ND6 ends with TAG, and ND4 ends with T.

The complete mitochondrial genome of Plexippus paykulli is a circular molecule of 14,316 bp in length, containing 13 protein-coding genes, 2 ribosomal RNAs, 22 transfer RNAs and a control region. The A + T content of the overall base composition of H-strand is 73.5% (T: 40.6%; C: 9.0%; A: 32.9%; G: 17.5%). ATP6, Cyt b, ND2, ND5 and ND4 genes begin with ATA as start codon; ATP8, ND1, ND3 and ND4L genes begin with ATT as start codon; COII and COIII genes begin with TTG as start codon; COI gene begins with AGA as start codon, while ND6 gene start with a typical ATG initiation codon. ATP6, COI, COII, COIII and ND3 genes are terminated with TAA as stop codon, ND6 ends with TA, ATP8, ND1 and ND2 end with TAG, Cyt b, ND5, ND4 and ND4L end with T.

The complete mitochondrial genome of Pholcus sp. is a circular molecule of 14,279 bp in length, containing 13 protein-coding genes, 2 ribosomal RNAs, 22 transfer RNAs, and a control region. The A + T content of the overall base composition of H-strand is 65.8% (T: 39.1%; C: 10.7%; A: 26.7%; G: 23.5%). COII and ND2 genes begin with GTG as start codon, COI, ND4L and ND5 genes begin with ATA as start codon, ATP8, ND1 and ND3 genes begins with ATT as start codon, while other five protein-coding genes start with a typical ATG initiation codon. ATP6, ATP8, COIII, ND2, ND4, ND4L and ND6 genes are terminated with TAA as stop codon, COI, Cyt b, ND1 and ND3 end with TAG, while COII and ND5 end with T.

The complete mitochondrial genome of Nephila clavata is a circular molecule of 14,433 bp in length, containing 13 protein-coding genes, 2 ribosomal RNAs, 22 transfer RNAs, and a control region. The A + T content of the overall base composition of H-strand is 76.1% (T: 40.0%; C: 9.2%; A: 36.1%; G: 14.7%). COI gene begins with TTA as start codon, COII gene begins with TTT as start codon, COIII gene begins with TTG as start codon, ND3, ND4L, ND6 and ATP8 genes begin with ATT as start codon, while other six protein-coding genes start with ATA as initiation codon. ND3, ND4, ND4L, ND5, COI, COII, ATP6 and ATP8 genes are terminated with TAA as stop codon, ND1, ND2, ND6 and Cyt b end with TAG, and COIII ends with TGA.

The complete mitochondrial genome of Argiope bruennichi is a circular molecule of 14,063 bp in length, containing 13 protein-coding genes, 2 ribosomal RNAs, 21 transfer RNAs, and a control region. The A + T content of the overall base composition of H-strand is 73.4% (T: 38.0%; C: 9.8%; A: 35.4%; G: 16.8%). ND6 begins with ATG, ND4 and ATP6 begin with ATA, ND5 and COI begin with TTA, ND1, COII and COIII begin with TTG, and other five protein-coding genes begin with TTG as start codon. ND5, ND4L, ND6, COI, COII, COIII, ATP6 and ATP8 genes are terminated with TAA as stop codon, Cyt b, ND1 and ND2 end with TAG, and other two protein-coding genes end with T.

The complete mitochondrial genome of Ophisaurus harti is a circular molecule of 17,163 bp in length, containing 13 protein-coding genes, 2 ribosomal RNAs, 22 transfer RNAs and a control region. The A + T content of the overall base composition of H-strand is 54.9% (T: 23.4%; C: 30.8%; A: 31.5%; G: 14.3%). COI gene begins with GTG as start codon, while other 12 protein-coding genes start with a typical ATG initiation codon. ND1. COI. ATP8. ATP6. ND4L and ND5 genes are terminated with TAA as stop codon, ND2. ND6 and Cyt b end with TAG, COIII ends with TA, COII and ND3 end with T and ND4 ends with TG.

The complete mitochondrial genome of sika deer (Cervus nippon) South Anhui population is a circular molecule of 16,429 bp in length, containing 13 protein-coding genes, 2 ribosomal RNAs, 22 transfer RNAs and a control region. The A + T content of the overall base composition of H-strand is 62% (T: 28.7%; C: 24.6%; A: 33.3%; G: 13.4%). ND2, ND3 and ND5 genes begin with ATA as start codon, ND4L gene begins with GTG as start codon, while other nine protein-coding genes start with a typical ATG initiation codon. ND1, COI, COII, ATP8, ATP6, ND4L, ND5 and ND6 genes are terminated with TAA as stop codon, ND2 ends with TAG, COIII, ND3 and ND4 ends with T, Cyt b ends with AGA.