The rugosa, also called the tetracorallia or horn coral, are an extinct order of solitary and

colonial Colonial or The Colonial may refer to: * Colonial, of, relating to, or characteristic of a colony or colony (biology) Architecture * American colonial architecture * French Colonial * Spanish Colonial architecture Automobiles * Colonial (1920 au ...

coral Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and sec ...

s that were abundant in Middle

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start ...

to Late

Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleoz ...

seas. Solitary rugosans (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 Rugose means "wrinkled". It may refer to: * Rugosa, an extinct order of coral, whose rugose shape earned it the name * Rugose, adjectival form of rugae Species with "rugose" in their names * ''Idiosoma nigrum'', more commonly, a black rugose trap ...

, wall. Some solitary rugosans reached nearly a meter in length. However, some species of rugose corals could form large colonies (e.g., ''

Lithostrotion ''Lithostrotion'' is a genus of Rugosa, rugose coral which is commonly found as a fossil within Carboniferous Limestone. ''Lithostrotion'' is a member of the family Lithostrotionidae. The genus ''Lithostrotion'', a common and readily recognised g ...

''). 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. Rugose corals have a skeleton made of

calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...

that is often fossilized. Like modern corals (

Scleractinia Scleractinia, also called stony corals or hard corals, are marine animals in the phylum Cnidaria that build themselves a hard skeleton. The individual animals are known as polyp (zoology), polyps and have a cylindrical body crowned by an oral di ...

), rugose corals were invariably

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...

, living on the sea floor or in a reef-framework. Some symbiotic rugose corals were

endobiont An ''endosymbiont'' or ''endobiont'' is any organism that lives within the body or cells of another organism most often, though not always, in a mutualism (biology), mutualistic relationship. (The term endosymbiosis is from the Greek language, G ...

s of

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.Stock, C.W. 2001, Stromat ...

, especially in the

Silurian The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleozo ...

period. Although there is no direct proof, it is inferred that these

Palaeozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and '' ...

corals possessed stinging cells to capture prey. They also had tentacles to help them catch prey. Technically they were carnivores, but prey-size was so small they are often referred to as microcarnivores.

Morphology

Streptelasma divaricans (Nicholson, 1875)

Rugose corals always show tabulae, horizontal plates that divide the corallite skeleton. The corallites are usually large relative to different types of coral. Rugose corals will sometimes have dissepiments, which are curved plates connected to septa and tabulae. The symmetry can be distinguished by the orientation of

septa The Southeastern Pennsylvania Transportation Authority (SEPTA) is a regional public transportation authority that operates bus, rapid transit, commuter rail, light rail, and electric trolleybus services for nearly 4 million people in five coun ...

in a transverse section of the coral. Rugose corals always display bilateral symmetry whereas tabulate and scleractinian corals show radial symmetry. Initially there are only 4 major septa; later minor septa are added in the 4 resulting spaces. The complex arrangement of septa is diagnostic of rugose corals. Rugose corals will also always have a columella, an axial rod which supports the septa running up the center of the corallite. It is present in rugose corals because they were mainly solitary and so required the extra support. Tabulate corals have no columella because they were always colonial and relied on the support of neighboring corallites.

References

{{Taxonbar, from=Q133091 Lopingian extinctions Ordovician first appearances