Two subclasses of cestodes are differentiated on the basis of the numbers of larval hooks, the Cestodaria being decacanth (10 hooks) and the Eucestoda being hexacanth (6 hooks). Collectively, 14 orders of cestodes have been identified according to differences in parasite morphology and developmental cycles.
Most meteorites originate between Mars and Jupiter, where a belt of asteroids has lingered for 4.5 billion years, since the solar system was young. No rock on Earth is as old as a meteoriteâall terrestrial material has been ground, melted, and reformed by plate tectonics. Meteorites have other, less common, origins. Meteor impacts on the moon or Mars can eject surface material into space that ends up on Earth. Last year a 10.5-ounce meteorite that originated on Mars fetched $94,000. A 4-pound lunar meteorite, the most expensive ever auctioned, sold for $330,000 in 2012.
Meteorites are the rarest types of rock found on Earth. Thousands of rocks are sent to laboratories each year by individuals thinking that they have found a meteorite. At best only one or two of these thousands is actually a rock from space. This article is designed to show the basic characteristics of meteorites.