Placozoans

You had muscles, and nerves, and specialised cells within you.  But they're not enabling you to survive, floating in the water.  In an example of evolution reversing direction, you lose all those features in favour of a flattened, simplified body, which crawls very slowly across smooth surfaces using flagella.

You are 'under the radar' for a food source for the other animals.  You survive, almost unnoticed into the present day, and are only recognised as an animal in the late 1800s.

That's as far as you can evolve here!  
You can go back to the start with the link above, or share what you became with the icons below.