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.
FlatwormsPlatyhelminthes. Structure. Flatworms are flat, soft bodied, ribbon shaped unsegmented, contain no body cavity, but they do have digestive cavity. They are bilateral symmetrical, while having only one opening. Flat worms have layers of tissues that surround their central gut. They are part of the acoelomates, and are considered hermaphroditic.