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 flatworms, nematodes are roundworms, and annelids are segmented worms. Flatworms are aceolomates, meaning they have no body cavities. The gut is completely surrounded by tissues and organs. Roundworms have a body cavity between the digestive tract and muscles. Segmented worms have a fluid-filled body cavity located within muscle tissue. In order from least advanced to most advanced: plateyhelminthes, nematodes, annelids.