There is evidence from a phylogenetically diverse sample of tunicates (Urochordata) that AGA and AGG code for glycine.  In other organisms, AGA/AGG code for either arginine or serine and in vertebrate mitochondria they code a STOP.  Evidence for glycine translation of AGA/AGG was first found in 1993 in Pyura stolonifera and Halocynthia roretzi. It was then confirmed by tRNA sequencing and sequencing whole mitochondrial genomes.