Comparison of the complete mitochondrial genome ofPhyllophorus liuwutiensis(Echinodermata: Holothuroidea: Phyllophoridae) to that of other sea cucumbers

Sea cucumber species are abundant (>1400 species) and widely distributed globally. mtDNA sequencing is frequently used to identify the phylogenetic and evolutionary relationships among species. However, there are no reports on the mitochondrial genome ofPhyllophorus liuwutiensis. Here, we performed mtDNA sequencing ofP. liuwutiensisto examine its phylogenetic relationships with other echinoderms. Its mitochondrial genome (15 969 bp) contains 37 coding genes, including 13 protein-coding genes, 22 tRNA genes and 2 rRNA genes. Except for one protein-coding gene (nad6) and five tRNA genes encoded on the negative strand, all other genes were encoded on the positive strand. The mitochondrial bases ofP. liuwutiensiswere composed of 29.55% T, 22.16% C, 35.64% A and 12.64% G. The putative control region was 703 bp in length. Seven overlapping regions (1-10 bp) were found. The noncoding region between the genes ranged from 1 to 130 bp in length. One putative control region has been found in theP. liuwutiensismitogenome. All of the tRNA genes were predicted to fold into a cloverleaf structure. In addition, we compared the gene arrangements of six echinoderms, revealing that the gene order ofP. liuwutiensiswas a new arrangement.