Short answers, pulled from the story.
Animals are multicellular eukaryotic organisms that consume organic material and breathe oxygen. They possess myocytes and can move during at least part of their life cycle. Reproduction occurs sexually in nearly all species.
Evidence of animals appears in rocks dating back roughly 650 million years ago. First body fossils appear in the Ediacaran period with forms like Charnia and Spriggina. Animals first appeared in the fossil record during the late Cryogenian period.
Over 1.5 million living animal species have been described by scientists. Estimates suggest as many as 7.77 million animal species may live on Earth. Around 1.05 million of these are insects alone.
Carl Linnaeus created the first hierarchical classification in Systema Naturae published in 1758. Original scheme placed animals among three kingdoms including classes like Vermes Insecta Pisces Amphibia Aves and Mammalia. Jean-Baptiste Lamarck began expanding this framework in 1793 calling Vermes a chaotic mess.
The largest terrestrial animal is the African bush elephant weighing up to 12.25 tonnes. The blue whale reaches up to 190 tonnes and measures over 30 meters long. Some Myxozoa parasites never grow larger than 20 micrometers.