1/17/12 7th Grade Notes - Worm Discussion

Flatworm

Roundworm

Earthworm

Courtesy of Google Images

Today we talked a little bit more about the three types of worms that exist in the world. Below is the table we filled out at the end of class.

	Flatworms	Roundworms	Segmented Worms
Phylum	Platyhelminthes	Nematoda	Annelids
Digestive System	No - Only 1 opening	Yes - Two openings Mouth & Anus	Yes - Two openings Mouth & Anus
Reproduction	Asexual - regeneration Sexual - Hermaphrodites that do not fertilize their own eggs	Asexual - Split in half Sexual - Hermaphrodites that do not fertilize their own eggs	Asexual - very rare Sexual - Hermaphrodites that do not fertilize their own eggs
Nervous System	No nervous system but a bunch of nerve cells	Yes, they have a brain and a nerve cord	Yes - they have a brain and a nerve cord
Circulatory System	Open circulatory system	Open circulatory system	Close circulatory system
Examples	Planarians, tapeworms	Hookworm, Trichina	Earthworm, Sandworm

One main difference I want to point out in the above chart is that flatworms do not have a digestive system while roundworms and segmented worms do. This is a huge adaptation that occurred allowing the roundworms and segmented worms to be more efficient eaters.

A second major adaptation that occurred in segmented worms was the fact it developed a close circulatory system. This allows the segmented worm to move blood faster throughout its body than a flatworm or roundworm.

Here is a cool website I found that interviews some of the different types of worms out there – http://yucky.discovery.com/flash/worm/pg000101.html