Genetics. 1998 Nov;150(3):1115-23.

Castresana J, Feldmaier-Fuchs G, Yokobori S, Satoh N, Pääbo S.

The mitochondrial genome of the hemichordate Balanoglossus carnosus and the evolution of deuterostome mitochondria.

AGA encodes Ser, AGG is absent, ATA encodes Ile, AAA is absent. “…out of the 69 ATA hemichordate codons, 20 occur in positions where Ile is conserved in >55% of the sequences (eight of these positions have Ile in >90% of the sequences), while none of them occur at positions where Met is conserved. Of the 19 AGA codons, 6 occur at positions where Ser is conserved in >55% of the sequences (3 of them with Ser in >90% of the sequences), whereas they are never used as stop codons.”