ABSTRACT
The nucleotide sequence of a large portion of the mitochondrial DNA (mtDNA) from the sea urchin Arbacia lixula, order of Stirodonta has been obtained. The sequence confirms that the genetic organization of mtDNA is identical to that of the two camarodont species, Paracentrotus lividus and Strongylocentrotus purpuratus, whose entire sequences are known.
Comparative analyses of the protein coding genes reveal that the two lineages of Camarodonta and Stirodonta evolved from a common ancestor under different directional mutation pressure thus leading to a different codon strategy.
