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.
Platyhelminthes, or Flatworms, are the simplest kind of worms. There are about 20,000 species in this group. They are found in many places and can be free living or parasitic. A parasite lives off of another living thing called a host and can be harmful. One of the most known flatworms is the tapeworm. Also, Flatworms are found in marine and fresh water. Type of Skeleton A flatworm has no skeleton, but has tiny bristles called cilia that help it move at least two layers of muscles under its skin. It has three cell layers called the endoderm, the mesoderm and the ectoderm. They also have the beginnings of a head region. They are a phylum of triploblastic acoelomate invertebrate animals. The word platyhelminthes comes from the Greek words 'platy' meaning flat and 'helmins' meaning worm. Their bodies are soft, unsegmented, dorsoventrally flattened with bilateral symmetry and resemble ribbons.
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.