A combination of factors is likely causing the decline of blue spruce trees throughout Michigan. Posted on March 7, 2011 by Dennis Fulbright, Michigan State University Extension, Department of Plant Pathology, and Jill OâDonnell, Michigan State University Extension.
Flatworms lack a respiratory or circulatory system; these functions take place by absorption through the body wall. Nonparasitic forms have a simple, incomplete gut; even this is lacking in many parasitic species. Movement in some flatworms is controlled by longitudinal, circular, and oblique layers of muscle.
1 They have a circulatory system and a digestive system. 2  Flatworms, roundworms, and segmented worms are all invertebrates. 3  Some species of each type of worm are free-living, meaning they are not dependent on another organism for food. 4  Segmented worms are the most complex animals of these three invertebrates. Students will then continue with their Internet research to compare flatworms, roundworms, and segmented worms by completing the Worm Comparison worksheet. 2  They should use their research to find more information in order to describe how these three types of worms are similar and how they are different.