J Mol Evol. 2004 Apr;58(4):376-89 doi:10.1007/s00239-003-2559-6

Gissi C, Iannelli F, Pesole G.

Complete mtDNA of Ciona intestinalis reveals extensive gene rearrangement and the presence of an atp8 and an extra trnM gene in ascidians.

Gene order varies even within the Ciona genus. A short atp8 gene is found in Ciona and Halocynthia.