when was it discovered?
It was  first encountered by Europeans in 1798
Platypus
When the platypus was first encountered by Europeans in 1798, a pelt and sketch were sent back to Great Britain by Captain John Hunter, the second Governor of New South Wales. British scientists' initial hunch was that the attributes were a hoax. George Shaw, who produced the first description of the animal in the "Naturalist's Miscellany" in 1799, stated it was impossible not to entertain doubts as to its genuine nature, and Robert Knox believed it might have been produced by some Asian taxidermist. It was thought that somebody had sewn a duck's beak onto the body of a beaver-like animal. Shaw even took a pair of scissors to the dried skin to check for stitches.
why is the platypus in the kingdom animalia Because they are multicellular eukaryotic organisms could you describe it? Dense, brown waterproof fur; webbed feet; elongated snout. and where is it found? Small streams and rivers at Tasmania and Australia how does it protect itself? The male's ankle spurs delivers venom for defence
wiki:25677055
Platypus [SEP] Taxonomy and etymology
When the platypus was first encountered by Europeans in 1798, a pelt and sketch were sent back to Great Britain by Captain John Hunter, the second Governor of New South Wales. British scientists' initial hunch was that the attributes were a hoax. George Shaw, who produced the first description of the animal in the "Naturalist's Miscellany" in 1799, stated it was impossible not to entertain doubts as to its genuine nature, and Robert Knox believed it might have been produced by some Asian taxidermist. It was thought that somebody had sewn a duck's beak onto the body of a beaver-like animal.