 Ebonwumons original name was Xuanwumon. Xuanwu (Black Tortoise).  Its Japanese counterpart was Genbu (Gen meaning "Phantom/Illusion").  Genbu was guardian of the north and his element was water. Note that  his second head is based that in some representation; Genbu was  represent as a Tortoise with a snake on him (episode 3.38  "Azulongmon Explains it All").