The "roundest" animal would most likely be some type of small marine invertebrate. If you mean "roundest" as in spherical, the roundest would probably be the Giant Ostracod, a tiny deep-sea crustacean and is completely sphere-shaped. If you mean round in terms of circular, you could include any creature with radial symmetry, such as many echinoderms (like sand dollars, sea urchins, etc.) and many cnidarians (jellyfish!). Pillbugs and hedgehogs can curl up into completely round, protective spheres, and pufferfish can inflate into a spherical shape.
it is an animal
Depends on the animal.
the biggest animal is the elephant
comparative - rounder superlative - roundest
Yes, roundest is an adjective. However, it may not always be appropriate, depending on the context.
It is 2,300
It is: 254.3
It is 0.188