Why do starfish have 2 stomachs?

Sea stars, commonly referred to as starfish, actually possess one stomach, not two. Their unique digestive system consists of a cardiac stomach and a pyloric stomach, but they do not operate as separate stomachs. Instead, they work in conjunction with each other to facilitate the digestion of food.

The cardiac stomach, also known as the eversible stomach, is located on the oral side of the sea star and can be extended through the mouth. This stomach is responsible for capturing and partially digesting food outside of the sea star's body. The food is enclosed in a membrane called the gastric pouch, and digestive enzymes are secreted into it. This initial breakdown of food occurs within the cardiac stomach.

Once the food has been partially digested in the cardiac stomach, it is returned to the body cavity through the mouth. The pyloric stomach, also called the central stomach, is located in the central disk of the sea star. The pyloric stomach receives the food from the cardiac stomach and further processes it. It contains digestive glands that release enzymes to complete the digestion of the food particles.

The nutrients extracted from the digested food are then absorbed by the pyloric stomach's walls and distributed to the rest of the sea star's body through its extensive circulatory system. Undigested materials and waste products are eventually expelled through the sea star's anus.

In summary, sea stars have a single, specialized digestive system consisting of the cardiac and pyloric stomachs, which work in sequence to break down and absorb nutrients from ingested food.