Animal Species/Other

Horn Eaters
Horn Eaters (ツノクイ, Tsuno Kui) are a type of creature featured prominently in the third One Piece movie. They are large herbivorous armadillo-like rhinos that will aggressively attack any horned creature within sight, even if said creature happens to have fake horns, as seen with Luffy (Usopp had him garbed in a ridiculous costume with antlers included). They are used by Butler to herd the various other horned animals on Crown Island in order to chop their horns off.

Trumpet Pig
A Trumpet Pig (トランペットブタ) is a weird pig living on the Crown Island.

Square Rhinos
Square Rhinos (四角いサイ) are animals with a rectangular form and loosely resemble rhinos that live on the Crown Island. When they lie on the ground, it is very easy to mistake them for rocks.

Hippo Rhino
A Hippo Rhino (カバサイ) is a sea beast with a hippo's head and a rhino's horn. It fell in love with the Going Merry.

Island Turtle
The Island Turtle (シマガメ), also known as Mecha Island, is a giant turtle that wakes every thousand years to lay its eggs.

Dragon
Oda has mixed the Monsters story into the One Piece main story, making Dragons a canonical species within One Piece, although whether they still exist in the present storyline is still unknown.

Dragons (竜（ドラゴン）) are large winged reptiles of great power and ferocity that are capable of breathing fire. One resided in the Wano Country long ago.

The powers and abilities of a dragon are so strong that not only can it destroy a single town (under the control of D.R. and Cyrano with the use of a Dragon Horn) and bring terror to the public, but killing one made the samurai Ryuma a legend, and stories about him are still passed down after generations.

Dragons were first mentioned by Hogback in the One Piece storyline during the Thriller Bark Arc, where he revealed to Zoro the story of Ryuma and his legendary slaying of a Dragon long ago which Zoro took in with much skepticism.

Dr. Vegapunk created his own artificial Dragon to guard Punk Hazard and it was incredibly strong, however this Dragon was slain by the Straw Hat pirates.

There are also two anime exclusive Dragon species, the Sennenryu and the Tatsunoko Dragon.