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.
Platyhelminths, or flatworms, include both free-living and parasitic species. The phylum Platyhelminthes is divided into two monophyletic clades, the Catenulida (with just around 100 known species; Larsson and Jondelius 2008) and the Rhabditophora, which includes nearly all known platyhelminths (Timothy et al. 2004; Willems et al. 2006; Larsson and Jondelius 2008).