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.
Stony meteoritesChondrites (85.7%)CarbonaceousEnstatiteAchondrites (7.1%)HED groupSNC groupAubritesUreilites Stony iron meteorites (1.5%)PallasitesMesosideritesIron meteorites (5.7%)Stony-iron meteorites are composed of approximately 50% nickel-iron and 50% silicate material. They make up only 1 to 2% of all meteorites.bout 33% of the meteorites are witnessed falls.A very large number of meteoroids enter the Earth's atmosphere each day amounting to more than a hundred tons of material. But they are almost all very small, just a few milligrams each. Only the largest ones ever reach the surface to become meteorites.