Platyhelminthes have incomplete alimentary canal.. whereas complete gut is observed from phylum Nematoda (Aschelmenthes) to phylum chordata

Platyhelminthes, also known as flatworms, have an incomplete digestive system. This means that they have only one opening to their digestive system, which serves as both the mouth and the anus. The food is ingested through the mouth and the undigested waste is expelled through the same opening.

Explanation:

Structure of Platyhelminthes Digestive System:
The digestive system of Platyhelminthes consists of a mouth and a gastrovascular cavity. The mouth is located on the ventral side of the body and leads to the gastrovascular cavity, which is lined with epithelial cells. The cavity is branched and extends throughout the body, allowing for the exchange of nutrients and gases.

Functioning of Platyhelminthes Digestive System:
Platyhelminthes digest their food extracellularly, meaning that the food is broken down outside of the cells. The enzymes secreted by the epithelial cells lining the gastrovascular cavity break down the food into simpler substances, which are then absorbed by the cells lining the cavity. The undigested waste is then expelled through the mouth.

Advantages of Incomplete Digestive System:
The incomplete digestive system of Platyhelminthes has certain advantages. It allows for a simple and efficient digestion process, as there is no need for a complex system of organs to digest and absorb nutrients. Additionally, the flat body shape of Platyhelminthes allows for easy diffusion of nutrients and gases throughout the body, making an elaborate digestive system unnecessary.

Conclusion:

Platyhelminthes have an incomplete digestive system, which consists of a mouth and a gastrovascular cavity. This simple digestive system allows for efficient digestion and absorption of nutrients, and is well-suited to the flat body shape of these organisms.