Planets orbit the Sun while moons orbit around planets. The amount of time required for a planet or moon to complete one orbit around another body is called an orbital period. On Earth, we call this orbital period a year. Our year is 365.256 days. On Mars it takes 686.98 days (Earth days, that is) to complete one orbit about the Sun--that's a long time to wait between birthdays!
They are true coelomates in which the coelom is lined both on the inside of the body wall as well as around the gut by mesoderm. Animals with a true coelom also have mesenteries, which suspend the body organs within the coelom.Animals higher to round worms such as annelids, arthropods, mollusks, echinoderms and chordates fall in this category. Tue coelomates are of the following types.(i) Schizocoelomates are true coelomates in which the body cavity originates by splitting of mesodermal tissue at the time of gastrulation.. Pseudocoelomates, in which a body cavity exists in addition to alimentary canal, but it is lined by mesoderm only on the outer body wall side and not around the gut. Examples are round worms (Nemathelminthes) and some minor phyla grouped under Aschelminthes. 3. Coelomates or Eucoelmates.
Schematic diagrams of the bodies of animals with coeloms, with pseudocoeloms, or without body cavities. In humans all but the cranial cavity develop from the coelom (pronounced SEE-lum). A coelom is a cavity that is entirely enclosed within cells derived from the middle layer of embryonic tissue. A few groups of animals, such as roundworms (Nematoda), have a body cavity that is only partly enclosed by tissue from the middle layer. Such a body cavity is called a pseudocoelom (pronounced SOO-doe-SEE-lum). In a few other groups, such as flatworms (Platyhelminthes), there is no body cavity.