This monster's Japanese name "Haidorōtasu" (ハイドロータス) is a portmanteau of "haidoro" (hydro) and "tōtasu" (tortoise).
This card is based on the Black Tortoise which is usually depicted as a turtle entwined together with a snake, and the god Xuan Wu (lit. "Dark" or "Mysterious Warrior") whose left hand is in the "three mountain hand seal" and right hand holds a sword.
It can be seen in the artwork that Hydrotortoise wears some sort of shield on his right arm, and the left arm and wing of "Aether, the Empowering Dragon" with green jewels on his left arm. He's also entwined by a snake.