Abstract: Acari, including ticks and mites, is one of the most diverse group of arthropods. In this paper, we reviewed the research progress in the 28 sequenced complete mitochondrial genomes of acari species. These mitochondrial genomes have several marked features: (1) There is significant variation in the size of mitochondrial genomes among the 28 acari species, and the mitochondrial genome of Panonychus citri (13 077 bp) is the smallest among all sequenced arthropods; (2) The base composition of all acari mitochondrial genomes are biased toward A and T, with six species harboring reverse GC-skew values (positive value); (3) The base composition and the position, length, copy number of the A+T-rich regions vary greatly among the 28 acari species, of which four tetranychid species harbor the highest A+T content within acari and the shortest A+T-rich region (44-57 bp) among arthropods; (4) High gene rearrangements are found in acari mitochondrial genomes, especially in those of Acariformes, but the rearrangements are not correlated to high taxonomic ranks; (5) The tRNA genes in some species of Acariformes are extremely truncated, presenting atypical cloverleaf structures. We suggest that it is necessary to sequence more acari mitochondrial genomes aiming to investigate whether these tRNA genes lacking both D- and T-arms are functional or not, to analyze the molecular mechanisms of evolution in acari mitochondrial genomes, and to carry out the acari mitochondrial transcriptome studies.

Key words: Acari, ticks, mites, mitochondrial genome, gene rearrangement, molecular evolution