Mohmoo

Mohmoo is a giant "sea cow" that was brought from the Grand Line by Arlong's crew. It was he who destroyed Gosa Village. However, when he encounters Luffy, Sanji, and Yosaku's boat, he is promptly beaten, and used to tow their boat to the island. Later, during the battle at Arlong Park, he is called upon by Hatchan to fight the Straw Hats. Despite memories of his first defeat, he does as told, only to be used in the Gomu Gomu no Kazaguruma, an attack by Luffy that takes out most of Arlong's forces, and then was thrown out of Arlong Park in the process, never to be seen again. Momoo is possibly an ophitauros. It can make a "mooo"ing sound like any cow. It has no problem staying on land, since Arlong's crew pulled it right through Gosa Village without it taking any known damage.