Prehistoric Hexacorallia genera

thumb|right|Thin-section view of Halysites corallum

Syringopora is an extinct genus of phaceloid tabulate coral. It has been found in rocks ranging in age from the Ordovician to the Permian, although it was most widespread during the Silurian, Devonian, and Carboniferous periods. Among other places, it has been found in the Columbus Limestone in Ohio, and in the Spring Branch Member of the Lecompton Limestone in Kansas.

Heliophyllum is an extinct genus of corals that existed predominantly in the Devonian. Heliophyllum is of the order Rugosa and can be referred to as horn corals. They were mostly solitary animals, although some were colonial. The genus had a wide distribution. Fossils of H. halli have been found in the fossil rich Floresta Formation of the Altiplano Cundiboyacense, Colombia. This genus used its nematocysts to stun prey.