Platyhelminthes: Digestive System & Feeding

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  • 0:03 Classification
  • 0:50 Bilateral Bodies
  • 1:36 Digestive System
  • 2:30 Eating
  • 3:45 Lesson Summary
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Lesson Transcript
Instructor: Jeremy Battista

Jeremy has a master of science degree in education.

The animal kingdom is a wonderfully diverse category of organisms. How, though, did we get from the simplest, single-celled organisms all the way to humans, the most complex? One stop along the way are the platyhelminthes.


Platyhelminthes refer to the phylum of the animal kingdom that includes the flatworms. The name 'platyhelminthes' literally means 'flat worm' ('platy' meaning flat and 'helminthe' meaning worm). A phylum is the first classification down from kingdom, the largest possible classification, so this includes a very broad classification of worms. While flatworms are in fact flat, they have a few specific features that distinguish them from other worms, including their digestive capabilities. There are three parasitic groups of platyhelminthes and one non-parasitic group. Parasitic platyhelminthes live in other animals and get their nourishment through them. Non-parasitic platyhelminthes eat their own food (more on that later).

Bilateral Bodies

All platyhelminthes are bilateral, meaning that the left and right hemispheres of the body are exactly alike. You could cut a flatworm lengthwise and all of the features would be the same on either side. Meanwhile, the top and bottom of the animal will look distinctly different. Imagine a flatworm as being like a snake: The head half is awfully different from the tail half, but drawing a line down the middle will create two symmetrical halves.

Unlike humans, platyhelminthes lack any real circulatory and respiratory systems. They have no body cavity, the space inside of a body, like a chest cavity, classifying them as acoelomates. Because they don't have any of these organs or spaces, flatworms tend to stay microscopic.

Digestive System

Despite their lack of circulatory and respiratory systems, flatworms do have long, interconnecting digestive systems which break down food and distribute nutrients all around the flatworm's body.

Each flatworm is different in terms of food consumption, but most platyhelminthes absorb nutrients by consuming them through a mouth. Food travels into a gut-type structure that holds and digests it. Once the food is broken down, the digestive system passes it all through the body. This allows nutrients to disperse evenly across the organism. The digestive tract branches out, sort of like a tree.

Similarly to humans, the food travels through their digestive tract, where it gets moved out into the body where needed. Unlike humans, however, most platyhelminthes don't have an anus, so after they've digested what they can, the unused food matter comes back out through their mouths.

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