Sirena is a huge and white-winged serpent, mentioned in European bestiaries as existing in the Arabian Peninsula. Its airspeed was so great that it could overtake a galloping horse and fall upon its victims. Its bites were so poisonous that its prey felt no pain. There is another Sirena in Spanish folklore that is a local variant of the siren.
John and Caitlin Matthews, The Element Encyclopaedia of Magical Creatures, 2013, Sirena, p 424