Complex sentence: The element "-dra" might also have been taken from the name of the prevolved form Seadra, to demonstrate the relationship, or perhaps Hydra, a mythical creature who dwelled in the seas.
Split into simpler sentences: The element "-dra" might also have been taken from the name of the prevolved form Seadra. It might also come from the Hydra, a mythical creature who dwelled in the seas.