👉 Exostratum is a type of exoskeleton found in animals, primarily in crustaceans, but also in some other groups such as mollusks and chordates. It consists of a hard outer layer called the exoskeleton that forms the skin of an animal's body. The exostrum is the part of the exoskeleton that provides support for the main skeleton and plays a crucial role in supporting the animal's weight, movement, and defense mechanisms.