'actinobranch' originates from Greek, specifically the word 'aktinos,' meaning 'ray,' and 'branchia,' meaning 'gills.'

'aktinos' and 'branchia' combined in Greek to form 'actinobranchia,' which eventually became the modern English word 'actinobranch.'

Initially, it referred to 'ray-like gills,' and this meaning has largely remained the same in modern usage.