Tatori is a tortoise-like creature found in Maridia, and is one of the most heavily armored creatures on Zebes. It has a large shell protecting its body, save for the legs, neck, and tail.
It is refered to as "Kame" in the game's code, which is simply the Japanese word for turtle.
The Tatori can retract its limbs and spin rapidly, allowing it to "jump" (possibly a reference to the Japanese kaiju Gamera). Samus can ride on its back as it does this to acquire an Energy Tank up higher on a Grapple Point, and Missile Expansion hidden in a wall.
Baby Tatori are also found in Maridia, and are the offspring of the Tatori. Normally the Tatori will not attack Samus, but should she attack one of its offspring Samus will be attacked by the spinning Tatori.