Trichoplax remains the simplest animal known on Earth having no mouth, no stomach, no muscles, no veins and even no blood. It even does not have front or back and is three cells thick only.
You won’t believe it is thinner than paper.
Trichoplax was accidently discovered in 19th Century by Franz Eilhard Schulze who was one of the best and top experts in Ocean sponges. He even had a laboratory full of beautiful and exotic sea creatures. Trichoplax was found hiding in a fishing tank and was dining on green algae that was growing in the surroundings.
It is believed that first animals on earth about 600-700 million years ago looked like Trichoplax. That means animals at that time must be flat and thinner than paper.
Surprisingly, these animals can fly (sort of) and are deadly poisonous. It can not only crawl but are expert swimmers as per study done for over a century by scientists.
These creatures also reproduce. The scientists know this because mixed breed had been found indicating that mixed breed creature had a mother and a father.
The scientists reported in 2014 that these creatures had neve cells and contain special set of proteins known as SNARE. This protein interestingly was found in some complex animals also.