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. (flatworms), a large group of bilaterally symmetrical free-living or parasitic invertebrates. The Platyhelminthes are classified as a subphylum of the phylum Scolecida or as a separate phylum. Flatworms range in length from 0.1 mm to several meters. The body is usually flattened and oval or somewhat elongate. It may be unsegmented or divided into several segments (tapeworms).