"Tetracorallia" from Ernst Haeckel's Kunstformen der Natur, 1904
Cross-section of Stereolasma rectum, a rugose coral from the Middle
Devonian of Erie County, New York
The Rugosa, also called the Tetracorallia, are an extinct order of
solitary and colonial corals that were abundant in Middle Ordovician
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, 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.
Rugose corals have a skeleton made of calcite that is often
fossilized. Like modern corals (Scleractinia), rugose corals were
invariably benthic, living on the sea floor or in a reef-framework.
Some symbiotic rugose corals were endobionts of Stromatoporoidea,
especially in the
Silurian period. Although there is no direct
proof, it is inferred that these
Palaeozoic 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.
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 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.
Streptelasma divaricans (Nicholson, 1875) from the Liberty Formation
(Upper Ordovician) of southern Ohio.
^ WoRMS (2015). "Rugosa". World Register of Marine Species.
^ "Rugosa". www.encyclopedia.com. A Dictionary of Earth Sciences.
Retrieved 20 February 2017.
^ Vinn, O; Mõtus, M.-A. (2014). "Endobiotic Rugosan Symbionts in
Stromatoporoids from the Sheinwoodian (Silurian) of Baltica". PLoS
ONE. 9 (2): e90197. doi:10.1371/journal.pone.0090197.
PMC 3934990 . PMID 24587277. Retrieved 2014-02-26.
^ Vinn, O; Wilson, M.A.; Toom, U.; Mõtus, M.-A. (2015). "Earliest
known rugosan-stromatoporoid symbiosis from the Llandovery of Estonia
(Baltica)". Palaeogeography, Palaeoclimatology, Palaeoecology. 431:
1–5. doi:10.1016/j.palaeo.2015.04.023. Retrieved 2015-06-18.
^ Ulrich, Ulrich; Hillmer, G. (2 Jun 1983). Fossil Invertebrates.
Cambridge University Press. pp. 69–71.