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.
Welcome to Meteor Crater. The worldâs best preserved meteorite impact site on Earth. Located just minutes from Interstate 40 in Northern Arizona near Winslow, Meteor Crater is the breath-taking result of a collision between an asteroid traveling 26,000 miles per hour and planet Earth approximately 50,000 years ago. Meteor Crater is nearly one mile across, 2.4 miles in circumference and more than 550 feet deep.