The relationships between stromatoporoids and heliolitids

The dense fibro-lamellar skeleton of lophiostromatids (Stromatoporoidea) is closely similar to the trabecular skeleton of protaraeids (Heliolitoidea) and, respectively, the cystose skeleton of labechiids is similar to that of proporids. They can be interpreted as different types of basal exoskeleton of colonial coelenterates. The main difference between these ancient stromatoporoids and heliolitids is in the arrangement of zooids in the colony, that in the heliolitids enabled them to participate in skeleton building, which was not possible in the stromatoporoids. The stratigraphical distribution supports the supposition of their cummon origin.