Platyhelminthes

Platyhelminthes, better known as flatworms, have a basic digestive system very similar to that of Cnidarians. They have a gastrovascular cavity in which digestion takes place, and a mouth through which food enters and waste exits. However, Platyhelminthes evolved both a pharynx and a branched gastrovascular cavity. The pharynx extends past the mouth during feeding, and uses muscular contractions and cilia to pull food into the mouth, similarly to how tentacles are used to direct food into the mouth of Cnidarians (Chapter 3 Flatworms(Platyhelminthes)). Additionally, the branched gastrovascular cavity allows food to be better transported around the body and more quickly digested, because there is more surface area in the gastrovascular cavity. Also, Platyhelminthes evolved to have their mouth located in the center of their body, as opposed to at one end as with most animals (Phylum Platyhelminthes – Boundless Open Textbook). However because Platyhelminthes lack a complete digestive system and specialized organs, they are not nearly as efficient as their more evolved counterparts.

This image depicts the Planaria digestive track. Planaria are part of class Turbellaria, under Phylum Platyhelminthes.

The above diagram depicts the branched gastrovascular cavity in Platyhelminthes, showing the pharynx extended through the mouth as it would be during feeding.

A flatworm can be seen digesting a snail above, with the snail positioned in the center of the flatworm’s body near its mouth and the pharynx being inserted into the snail to secrete digestive enzymes.