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.
Sponges and jellyfish lack specialized organs for gas exchange and take in gases directly from the surrounding water. Flatworms and annelids use their outer surfaces as gas exchange surfaces. Arthropods, annelids, and fish use gills; terrestrial vertebrates utilize internal lungs. Gas exchange systems in several animals.