Final answer:
The type of skeletal system composed of a hard skeletal layer found on the exterior of the organism is called an exoskeleton.
Step-by-step explanation:
The type of skeletal system of animals that is composed of a hard skeletal layer found on the exterior of the organism is an exoskeleton. An exoskeleton is a hard external skeleton that protects the outer surface of an organism and enables movement through muscles attached on the inside. Some examples of animals with exoskeletons include insects, crustaceans, and arachnids.