> Your statement lacks definition of what exactly is a "stomach", and I don't think you can provide such a definition for it to classify animals correctly. Spon

> Your statement lacks definition of what exactly is a "stomach", and I don't think you can provide such a definition for it to classify animals correctly. Sponges (which are animals), for instance, don't really have a "stomach", there is no cellular differentiation based on that function. To be fair to sponges, they are considered the first branch of the animal kingdom - direct descendants of the first digestive tract and the first organism with any sort of cellular specialization. They're what animals would look like if they were nothing but a stomach.