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.
Acoelomates: The Phylum Platyhelminthes (Flatworms) In our discussion of the bilateria, we begin with those organisms that do not have a body cavity (the acoelomates). These organisms do not have a fluid-filled internal body cavity, but instead, have a relatively solid body mass. The phylum Platyhelminthes is divided into four classes.