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. are commonly called flatworms. There are both. parasitic. (dependent on a host organism for survival) and. free-living. forms of this group. Flatworms, either parasitic or free-living forms, have both sexes on the same individual, a condition referred to as. hermaphroditic. .ost Nematodes are free-living, but some are important parasites of plants and animals. As for the flatworms, nematode development includes all three embryonic tissue layers. Roundworms have a fluid-filled body cavity, that is lined on the outside by tissue derived from mesoderm.