Sponge reef
Sponge reefs are reefs produced by sea sponges. All modern sponge reefs are formed by hexactinellid sponges, which have an endoskeleton made of silica spicules and are often referred to as "glass sponges", while historically the non-spiculed, calcite-skeletoned archaeocyathid and stromatoporoid sponges were the primary reef-builders.