Simplify the following text for a Grade 9 native English-speaking person.
Original: The group has hardly changed in millions of years ; the modern horseshoe crabs look almost identical to prehistoric genera such as the Jurassic Mesolimulus , and are considered to be living fossils .
Simplified: The group has hardly changed in millions of years . The modern horseshoe crabs look almost identical to prehistoric genera such as the Jurassic Mesolimulus , and are considered to be living fossils .