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.
Some impact craters on the moon measure more than 600 km (375 miles) across. On April 11th, 2006 the large Valley of the Sky iron meteorite, measuring 376 by 38 by 36.8 centimetres sold at auction for $93,000 (USD). About 500 to 600 meteorites fall to Earth each year. Most fall into the sea or in unpopulated areas (lucky us). The largest meteorite ever found is the Hoba iron meteorite which was found in 1920 on the Hoba West Farm, near Grootfontein, Namibia. Although it's the largest meteorite ever found, the Hoba left no visible crater. It is thought to have landed over 80,000 years ago and was found by a farmer ploughing his land.