What are flatworms? - tapeworms and other things
Welcome to Quatr.us Study Guides!

What are Flatworms?

Flatworm
Flatworm

The first flatworms, or platyhelminthes, probably evolved from something like a hydra about 550 million years ago. Like all other living things at this time, these early flatworms all lived in the ocean. A flatworm has a body shaped roughly like a bag, like the earlier hydras.

Flatworms were the first animals that had bilateral symmetry, instead of radial symmetry like a hydra, or no symmetry at all like a sponge. Bilateral symmetry must have been a big advantage, because nearly all later animals had bilateral symmetry. Inside, flatworms had a nervous system with most of the senses concentrated in the head end, so that when the flatworm moved forward, the head, which was in front, could detect danger in time to escape it. Besides this early brain, there were just two long neurons that ran the length of the flatworm's body. On top of the head, there were simple eyes that could sense light, like the eyespots on some eukaryote cells.

To get food, a flatworm took in food through its mouth, which was about halfway down its body, and then it excreted its poop out through its mouth again. Flatworms had no circulatory, respiratory, or skeletal system. Because they're so flat, most of their cells were on the surface, so they could get enough oxygen and food directly from the water around them. Flatworms did have some cells that were like early versions of kidneys - these helped keep the right amount of water in the flatworm's body.

Tapeworm
A nine inch long tapeworm from inside a cat.
Thanks to dogbreedinfo!

Probably around 545 million years ago, not too long afterwards in terms of evolution, some of these flatworms evolved into roundworms. But there were still plenty of flatworms around too, and there still are, today. Some flatworms now live independently in the oceans, and some live in fresh water, while others live inside people and animals, both in the ocean and on land. Flatworms that live inside people are tapeworms and flukes. Tapeworms have lived inside people and animals for so long that they don't even have a digestive system anymore. They just get their food predigested by the animals they're living in.


Did flatworms kill off the Neanderthals?
Roundworms

Bibliography and further reading about flatworms:

Roundworms
Biology
Quatr.us home


Please help other teachers and students find us: link to this page from your class page.
Karen Carr is Associate Professor Emerita, Department of History, Portland State University. She holds a doctorate in Classical Art and Archaeology from the University of Michigan. Follow her on Instagram, Pinterest, or Twitter, or buy her book, Vandals to Visigoths.
Karen Carr is Associate Professor Emerita, Department of History, Portland State University. She holds a doctorate in Classical Art and Archaeology from the University of Michigan. Follow her on Instagram or Twitter, or buy her book, Vandals to Visigoths.
Sign up for more free articles and special offers in Quatr.us' weekly newsletter:
We will never share your e-mail address unless you allow us to do so. View our privacy policy. Easy unsubscribe links are provided in every email.
Check out our new ebook: Short and Simple: Ancient Greek Myths! - just out! Twenty-five easy to read, illustrated stories, from Pandora to Medea, Icarus, and the Trojan Horse (you can read these online as samples). Get it this week for just $14.99, five dollars off the regular price of $19.99.
Cite this page
  • Author: K.E. Carr
  • Title:
  • Site Name: Quatr.us Study Guides
  • Publisher: Quatr.us
  • Date Published:
Did you find what you needed? Ask your teacher to link to this page so other people can use it too! Send it in and win a Quatr.us "Great Page!" award!
Sign up for more free articles and special offers in Quatr.us' weekly newsletter:
We will never share your e-mail address unless you allow us to do so. View our privacy policy. Easy unsubscribe links are provided in every email.
Comment on This Article
Quatr.us is loading comments...
(Comments will appear after moderation, if they are kind and helpful. Feel free to ask questions, and we'll try to answer them.)
Cite this page
  • Carr, K.E. . Quatr.us Study Guides, . Web. 23 June, 2017
ADVERTISEMENT