The one-way flow of material through the gut makes it possible for the gut to become specialized at different regions. As the food moves along in one direction, certain portions of the digestive tract function in storage, grinding, and absorption. The unidirectional gut also allows the organism to keep eating while digesting and defecating. The more efficient digestion of food is important, especially for large, very motile animals that require large amounts of energy. As body size increases, a means of active respiration to transport oxygen to those tissues not in direct contact with oxygen becomes more important.
Snails can be marine , aquatic , or terrestrial .
If you squeeze the balloon at one end, the water must go somewhere, so it stretches the other end out, causing elongation. Because each segment of an annelid has its own set of circular muscles , and there is partial compartmentalization of the coelomic fluid by septa , the worm is able to control its movements. Metamerism most likely evolved as an adaptation to a burrowing lifestyle. The members of this phylum, particularly the polychaete worms, have different types of lifestyles. We will look at one of these, paying particular attention to modes of feeding and locomotion .