Trichoplax really started as a ‘skin’ for a video game. The entire time I’ve been developing the story I have always kept in mind how it could work with the game mechanics and rules. I’ve always figured the appearance was affected by the character strengths and weaknesses. You should in theory be able to guess a character from the impression you get from their looks. If they are muscular then you can safely assume they are strong. That sort of thing.