Complete mitochondrial genome of a Chinese scorpion Mesobuthus martensii (Chelicerata, Scorpiones, Buthidae).

The complete mitochondrial genome (15,034 bp) of a Chinese scorpion Mesobuthus martensii (Buthidae) was sequenced and characterized in detail. The genome contains 13 protein-coding genes, 21 transfer RNA genes, two ribosomal RNA genes and a large non-coding region ( = CR). Its gene arrangement pattern is identical to that of Limulus polyphemus (Chelicerata, Xiphosura), with the exceptions of the tRNA(Glu)-tRNA(Ile)-tRNA(Met) (Q-I-M) arrangement and tRNA(Asp)-loss. Additional interesting features are found and discussed: high frequency of Leu(UUG) codon use, low A+T content of the genome (66.75%), and six repeat units (five 60-nt-long and one 58-nt-long repeats) in the 998-nt CR. Bayesian analysis based on amino acid sequences of the 12 proteincoding genes (excluding ATP8) reveals that the family Buthidae (Order Scorpiones) and the class Arachnida form strong monophyletic groups within Chelicerata, respectively. It indicated that the scorpions are the most ancestral arachnids.