Platyhelminthes are the simplest animals that are bilaterally symmetrical and triploblastic ( composed of three fundamental cell layers). Another name for "platyhelminthes" is flatworms. These flatworms have no body cavity other than the gut (they even lack an anus). A common misconception is that all flatworms are parasites. This is not entirely true, there are plenty of flatworms that can survive their whole lives without exhibiting parasitic behavior.
  • Platyhelminthes use the same pharyngeal opening to take in food and expel waste. They also have a very highly branched gut in order to transport food to all parts of the body.

Flatworms were once divided into three groups:

Turbellaria- found in the oceans, in fresh water, and in moist terrestrial habitats, and a few are parasitic.
Just hanging out in the water. What's up?
Just hanging out in the water. What's up?

Trematoda- all parasitic and have life cycles specialized for parasitism in animal tissue.
I like tissues
I like tissues

Cestoda- tapeworms and intestinal parasites in vertebrates.

YUM! Nutritious!
YUM! Nutritious!

General Characteristics of Platyhelminthes:*
1)Bilaterally symmetrical.
2)Body having 3 layers of tissues with organs and organelles.
3)Body contains no internal cavity.
4)Possesses a blind gut (i.e. it has a mouth but no anus)
5)Generally flattened.
6)Reproduction mostly sexual as hermaphrodites.
7)Mostly they feed on animals and other smaller life forms.
8)Some species occur in all major habitats, including many as parasites of other animals.

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