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.
Platyhelminthes or flatworms are unsegmented, bilaterally symmetrical acoelomates. They have ciliated, soft, dorsoventrally flattened worm-like bodies with an incomplete gut. About 20,000 species of Platyhelminthes are known up to date.