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.
Introduction. Platyhelminthes, or flatworms, are considered by many to be ancestral to most of the metazoans that were to follow and for the first time we see the development of the final germ layer, the mesoderm, with its potential to form muscles and other structures.ut, unlike the other animals that are to follow, in flatworms the mesoderm remains as a solid mass of tissue without a coelom and the advantages that this adaptation could have provided to the group are lost. This probably explains why most of today's flatworms are parasitic rather than free living.