What kind of skeletal system does a sponge have?

Sponges do not have a skeletal system. They are supported by a flexible network of spongin fibers and collagen. This network is called a mesohyl. The mesohyl is made up of a gelatinous substance that contains spicules, which are small, needle-like structures made of calcium carbonate or silica. The spicules help to support the sponge and protect it from predators.