In geophysics the refraction or reflection of seismic waves is used for research into the structure of the Earth's interior, and man-made vibrations are often generated to investigate shallow, subsurface structures.
Flatworms are considered acoelomate, since they have no body cavity, and roundworms are pseudocoelomate because they have a body cavity, but it is not derived from the splittiâ¦ng of the mesoderm tissue. Also, flatworms only have one opening in their digestive system unlike roundworms with two.
The body plan of the flatworm is bilateral, with a head that leadsâa plan that continues in most animals living today. The structure of this bilateral plan is ideal for an active hunter. MS-LS1.D. Flatworms are the first animals to transmit signals from sensory receptors along nerve cells to the brain.:49. The flatwormâs bilateral body plan has a head with a brain and stereo eyes that enable it to actively hunt. Its mouth and pharynx are in the center of its underside.