Which PHP SPL Exception should you throw if a class doesn't exists? within the context of ZF2 coding standards for exceptions.
In the standards it say exceptions should extend from one of PHP's SPL Exceptions. My first guess would be that it's some kind of RuntimeException.
Depends on the context of your application.
If you are receiving the class name as a method argument and you try to load that class in the same method then the you should use an InvalidArgumentException exception.
If you are receiving the class name from a field value or from a method then you should use RuntimeException