Stromatoporoidea

Stromatoporoidea is an extinct clade of sea sponges common in the fossil record from the Ordovician through the Devonian. They were especially abundant and important reef-formers in the Silurian and most of the Devonian. The group was previously thought to be related to the corals and placed in the Phylum Cnidaria. They are now classified in the phylum Porifera, specifically the sclerosponges. There are numerous fossil forms with spherical, branching or encrusting skeletons of laminated calcite with vertical "pillars" between the "laminae". Specimen of its oldest genus, "Priscastroma", have been found within the Middle Ordovician Sediments. This same genus has been referred to as the species "P. gemina" Khrom., and is known to have been known to branch off into two forms, A and B. Form A gave rise to the genus "Cystostroma" while form B gave rise to the genus "Labechia" and its descendants. Paleozoic stromatoporoids died out at the Hangenberg Event at the end of the Devonian. Purported Mesozoic stromatoporoids may be unrelated, thus making "stromatoporoids" a polyphyletic group if they are included.
Stromatoporoids are useful markers whose form and occurrence can diagnose the depositional environment of sedimentary strata. Paleozoic stromatoporoids hosted various symbiotic endobionts such as rugosans, syringoporids, worms and cornulitids.