The original German spelling *ö*yena is correctly transliteraded in *oe*yena. But the spelling oyena is kept on the basis of prevailing usage. See nomenclatural details in Ref. 83466 and Eschmeyer (CofF ver. Mar. 2011: Ref. 86697).
Etymology of Generic name :
Name from Latin 'labrum' for lip, rim or edge; referring to the big lips of the fishes of the genus (from Ovid and Pliny according to Petrus Artedi).