"The Rugosa, also called the Tetracorallia, are an extinct order of solitary and colonial corals that were abundant in Middle Ordovician to Late Permian seas.
Solitary rugosans ...
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(e.g., Caninia, Lophophyllidium, Neozaphrentis, Streptelasma) are often referred to as horn corals because of a unique horn-shaped chamber with a wrinkled, or rugose, wall. Some solitary rugosans reached nearly a meter in length. However, some species of rugose corals could form large colonies (e.g., Lithostrotion). When radiating septa were present, they were usually in multiples of four, hence Tetracoralla in contrast to modern Hexacoralla, colonial polyps generally with sixfold symmetry." - (en.wikipedia.org 18.12.2020)
