would guess that the Tardigrade would be it.

They are classed as the smallest mammals. An amoeba is the smallest animal in the world. It is a single cell organism. When does an animal become an animal? When an animal's egg is fertilized it becomes another animal life form and you could argue that this would then be the smallest animal.

top 10 animals in world, animals

http://clipmarks.com/clipmark/57F02A35-BDCE-46DC-A18F-B4135996A429/

http://www.mixx.com/stories/2626965/10_of_the_world_s_smallest_animals

http://www.news-world.us/pics/2008/11/03/10-of-the-worlds-smallest-animals/

http://www.funonthenet.in/articles/smallest-animals.html

http://scienceray.com/biology/zoology/10-of-the-worlds-smallest-animals/

World's Smallest Seahorse: 16 mm (0.6-inch) long

The creature, known as Hippocampus denise, is typically just 16 millimetres long - smaller than most fingernails. Some were found to be just 13 mm long. H. denise lives in the tropical waters of the western Pacific Ocean, between 13 and 90 metres beneath the surface.

World’s Smallest Cattle: 81 cm (31-inch) height

The world’s smallest cattle is a rare breed of an Indian zebu called the Vechur cow. The average height of this breed of cattle is 31 to 35 inches (81 to 91 cm). The photo above shows a 16 year old Vechur cattle as compared to a 6 year old HF cross-breed cow.

World's Smallest Lizard: 16 mm (0.6-inch) long

So small it can curl up on a dime or stretch out on a quarter, a typical adult of the species, whose scientific name is Sphaerodactylus ariasae is only about 16 millimeters long, or about three quarters of an inch, from the tip of the snout to the base of the tail. It shares the title of "smallest" with another lizard species named Sphaerodactylus parthenopion, discovered in 1965 in the British Virgin Islands.

World's Smallest Chameleon: 1.2 cm (0.5-inch) long

The Brookesia Minima is the world's smallest species of chameleon. This one is just half an inch. Found on the rainforest floor of Nosy Be Island off the north-west coast of Madagascar, females tend to be larger than males.

World's Smallest Hamster: 2.5 cm (0.9-inch) tall

Only slightly bigger than a 50p piece, PeeWee is the smallest hamster in the world. Weighing less than an ounce, the golden hamster stopped growing when he was three weeks old - his five brothers and sisters went on to measure between 4in and 5in.