Suborder HELIOLITINA, Upper Ordovician - Middle Devonian. These corals are very different from other tabulate corals, that they were regarded as separate subclass from tabulata. They are devided into Helioliticae (coenenchymal tissue consists of tubuli, Fig. 3A), Proporicae (coenenchymal tissue consists of dissepiments, Fig. 3B) and Coccoseridicae (primitive corals, which have thickened trabecular skeleton, Fig. 3C). Heliolitids are abundant in the cliffs of northern Saaremaa (Propora tubulata, Heliolites interstinctus). Among the oldest heliolitids in the world are Protaraea procella from the Vasalemma Nordkalk quarry and Protaraea diffluens from the outcrops of East-Estonia.