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.
Even hydras, which are primitive, radially symmetrical cnidarians, show some degree of cephalization. They have a âheadâ where their mouth, photoreceptive cells, and a concentration of neural cells are located. Flatworms (phylum Platyhelminthes) are the most primitive animals with bilateral symmetry.They also have a fairly advanced degree of cephalization, with sense organs (photosensory and chemosensory cells) and a brain concentrated at the anterior end.his process eventually produces a head region with sensory organs. Cephalization is intrinsically connected with a change in symmetry. It accompanied the move to bilateral symmetry made in flatworms, with ocelli and pinnae placed in the head region.