The complete mitochondrial genome of the clam Meretrix petechialis (Mollusca: Bivalvia: Veneridae).

Veneridae is a diverse, commercially important, and cosmopolitan family. Here we present the complete mitochondrial genome of the clam Meretrix petechialis (Bivalvia: Veneridae). The genome is 19,567 bp in length, and contains 36 genes including 12 protein-coding genes, two ribosomal RNAs, and 22 transfer RNAs (tRNAs). All genes are encoded on the same strand. In contrast to the typical animal mitochondrial genomes, it lacks the protein-coding gene atp8. The other distinct features of the mitochondrial genome are that it has only one copy of trnS and a duplication of the trnQ gene. Mitochondrial gene orders are most highly rearranged in the class Bivalvia. Comparing the gene arrangements between M. petechialis and Venerupis philippinarum, we observe that they share four completely identical gene blocks, two large gene blocks cox1-L1-nad1-nad2-nad4L-I and cox2-P-cytb-rrnL-nad4-H-E-S2-atp6-nad3-nad5, and two small gene blocks containing tRNA genes only. After excluding tRNAs from the comparison, the gene arrangements between M. petechialis and V. philippinarum are the same except for translocations of the genes rrnS and cox3. We also present comparisons of gene arrangements between other molluscan species.