For Arthropod Mitochondria, Variety in the Genetic Code Is Standard - journal.pbio.0040175.g001

The horseshoe crab uses the newly discovered genetic code (AGG translates into lysine rather than serine). Parallel evolution of this and the typical code of invertebrate mitochondrial genomes (which is correlated with tRNA mutations) occurred repeatedly along the evolutionary history of arthropods. (Figure: horseshoe crab lithograph by George Endicott)