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.
Phylum Platyhelminthes (the flatworms) ~1300 species ie: Planarians, Tapeworms, Flukes Some are free living and some are parasitic. Soft, flattened worms with tissues and internal organ systems.The simplest animals to have 3 germ layers, bilateral symmetry, and cephalization.ilaterally symmetrical: Most primitive bilaterally symmetrical organism Acoelomate: but no coelom Coelom-fluid filled body cavity, lined with tissue derived from mesoderm. Size range:1 mm to several meters More complex than porifera and cnidarians, but the least complex worm phylum.