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.
Food enters the mouth and is digested in the intestine; the nutrients diffuse throughout the body (there are no circulatory or respiratory systems). The undigested materials are discharged from the mouth (there is no anus). Ribbon worms have more highly developed circulatory and digestive systems. Prey, such as small ï¬sh and polychaete worms, are speared by a sharp, sticky extension called a proboscis, which the ribbon worm extends from a recessed area in its head region.