Question

Describe the evolution of specialized cells, tissues, and organs in Animalia, including the name of the animal group that first showed each evolutionary innovation.

Answer 1

Sponges are the group in which the first specialized cells appeared. However, sponges are merely loose collections of such cells. The cnidaria was among the first animals to evolve true, differentiated tissues. Flatworms were among the first animals to evolve true organs.