How do marine invertebrates defend themselves?

Since marine invertebrates have no internal skeleton many of them have an exoskeleton or a hard external shell that helps protect them from predators.  However, there are many marine invertebrates that have no external shell or exoskeleton and have developed other methods of defense.  These methods include camouflage, the ability to sting predators, and bright colors to ward off predators by advertising that they are poisonous.