Spicules: structural elements found in most sponges that provide structural support, like a skeleton. Spicules can be made of silica or calcium carbonate.
Although sponges do not have organized tissue, they depend on specialized cells, such as choanocytes, porocytes, amoebocytes, and pinacocytes, for specialized functions within their bodies.
The skeletal elements of the sponge are produced by the amoebocytes. The amoebocytes produce spongin, the soft fiber that forms natural bath sponges.