a row of photophores along the base of the anal fin and lower side of the caudal peduncle (not including the Prc\'s at the base of the caudal fin) in Myctophidae. Usually divisible into AOa mostly above the anal fin base and AOp mostly on the caudal peduncle. In some older works AO refers to the antorbital photophores
Dictionary of ichthyology. 2009.