Extinct group that has been attributed to the Hydrozoa, sponges (Porifera), foraminifera (Foraminiferida), Bryozoa, or algae, or regarded as a phylum with no modern representatives. Stromatoporoids are calcareous masses built up of horizontal layers (latilaminae) and vertical pillars. The calcareous skeleton is called the coenosteum. The upper surfaces show a pattern of polygonal markings and may have swellings (mammelons) and stellate grooves (astrorhizae). They are found in limestones of Cambrian to Cretaceous age, often forming reefs in Ordovician to Devonian times.