Answer: The spicules of the sponges are made up of calcium carbonate and silica. These structures are present in the body of sponges to provide them support and protection.
The sponges have the endoskeleton in the body which is developed by the specialized cells of the body.
The endoskeleton of the sponges are known as spicules. Actually the outer body of the sponges are very soft and internally has endoskeleton for protection which is a bit hard as it is made of silicon dioxide or calcium carbonate.
