Sphaeractinoidea

(paleontology) An extinct group of fossil marine hydrozoans distinguished in part by the relative prominence of either vertical or horizontal trabeculae and by the presence of long, tabulate tubes called autotubes.

An extinct group of fossil marine sponges closely related to modern Sclerospongiae and fossil Stromatoporoidea. They may have appeared as early as Late Carboniferous (Pennsylvania Period) of the Late Paleozoic Era. They were definitely present during the Permian Period at the close of the Paleozoic and flourished during the Mesozoic Era, especially during the Jurassic and Cretaceous, declining rapidly during the late Cretaceous, and may have persisted until Eocene time, during the Cenozoic Era.

Like the stromatoporoids, they have a radial canal system; in vertical thin section the skeleton is calcareous and characterized by a latticelike pattern. The vertical structures are round, short to long rodlike pillars. However, unlike the stromatoporoids, the horizontal component of the reticulum is trabecular or rodlike rather than separated parallel or concentric plates, or they may be thin, flat, or broadly arched cyst plates. See also Sclerospongiae; Stromatoporoidea.