Simplify the following text for a Grade 6 native English-speaking person.
Original: True crabs are decapod crustaceans of the infraorder Brachyura , which typically have a very short projecting `` tail '' ( = short , = tail ) , or where the reduced abdomen is entirely hidden under the thorax .
Simplified: Crabs have very short tails . A crab 's tail and reduced abdomen is entirely hidden under the thorax .