Which of these systems (digestive, nervous, reproductive) first appeared in flatworms?

A feature of flatworms is the appearance of a new germ layer, which is responsible for the formation of organs and their systems. The leaf is called the mesoderm. For the first time in flatworms, a nervous system appears that looks like nerve trunks stretching along the sides of the body. The trunks are connected to each other along the entire length by jumpers. The nervous system can be attributed to the accumulation of components of the nervous tissue in the front of the body, which led to the emergence of such senses as sight, touch and smell. A digestive system is formed, consisting of two sections (front and middle), cavity digestion occurs. For the first time, the reproductive system appears, it consists of the gonads and appendages.