Spicules may be made of silica or calcium carbonate, and vary in shape from simple rods to three-dimensional "stars" with up to six rays. Spicules are produced by sclerocyte cells, and may be separate, connected by joints, or fused.

Sponge Spicules

Spicules may be made of silica or calcium carbonate, and vary in shape from simple rods to three-dimensional…