Starfish
Starfish have a complete digestive that includes a mouth on the underside, known as the oral side, and an anus on their upper side. As seen in the picture, the food is brought through the stomach and passes through their tube feet into their mouthes. After this, the waste and extra, unnecessary particles are eliminated through the anus.
Sand Dollar
Similar to that of a starfish, the sand dollar also has a mouth located on its underside, as well as a anus located on its top side. The sand dollar uses little tube feet to eat and breathe. Its jaw has five teeth like sections that chew up the plants and animals that it eats. The digestive process can take almost two days. The food travels through the inside of the sand dollar over a period of time, and its wastes are eliminated via the anus.
Sea Urchin
A sea urchins mouth is made up of five teeth, similar to the sand dollar, and it has a tongue that breaks down food. Digestion occurs in the intestines of the sea urchin. The small intestine makes a complete wrap around the inside of the urchin, and than is connected with the large intestine. From that, the sea urchin has a rectum and an anus, in which the excretion of food and waste is completed.