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.
The body plan of the flatworm is bilateral, with a head that leadsâa plan that continues in most animals living today. The structure of this bilateral plan is ideal for an active hunter. MS-LS1.D. Flatworms are the first animals to transmit signals from sensory receptors along nerve cells to the brain.:49. The flatwormâs bilateral body plan has a head with a brain and stereo eyes that enable it to actively hunt. Its mouth and pharynx are in the center of its underside.