Mitochondrial gene order and comparison of C. hongkongensis , C. gigas and C. virginica . Genes are abbreviated as in the text. Noncoding regions are indicated by white boxes. Locations of trnM-like and trnK-like structure in C. gigas are hatched. Section between dotted lines is the region in which significant gene order rearrangements are present among the three oysters ("hot spots" of rearrangements). Segment between dash lines and arrows indicate the region present in C. gigas but absent in C. hongkongensis.