Corals (Phylum Cnidaria)

© Craven & Pendle Geological Society

Amplexus coralloides
(Sowerby 1814)

A Tabulate Coral

Syringopora
Goldfuss 1826

Dibunophylum

Dibunophylum bipartitium
M'Coy

Dibunophylum in section

Dibunophylum bipartitium
(cross section)

Corals are marine animals related to the jellyfish and sea anemone. They are a soft bodied animal (polyp) that lived in a calcareous skeleton (corallum). There are three groups (or orders) - Rugosa, Tabulata and Scleractinia. Tabulate and Rugose corals are commonly found in our Carboniferous limestone.  They can be either compound or single often possessing a cylindrical body. In life they would have had a central mouth surrounded by a ring of tentacles. The growth of the coral is reflected in the development of the skeleton. Corals in fact began to dominate as early as the late Precambrian i.e. in the Ediacaran Period.

Rugose corals can be either solitary or colonial and bilaterally symmetrical. In cross-section the arrangement of septa and dissepiments are commonly used in identification. The The Rugosa died out in the end-Permian mass extinction and are not believed to be ancestral to post-Palaeozoic Scleractinia.

Tabulate corals are colonial although they do possess many closely spaced tabulae. Unlike Rugose corals, septa and dissepiments are absent or weakly developed. The long slender corallites of Syringopora are typical of this Order. Although these corals have a shared common ancestor with the Rugosa, the Tabulata are not thought to be directly descended from the Rugosa.

Amplexus coralloides (a Rugose coral) is typically found in Mississippian shallow water limestones and commonly around Waulsortian mud mounds throughout Europe, Asia and N.America.

Amplexus is a found as a solitary, cylindrical-type coralla.  The wall of the coral is very thin.  Also major septa are thin, minor septa frequently absent and there are no dissepiments.  The tabulae is complete, flat and with downturned margins and cardinal fossula depression.

Syringopora (a Tabulate coral) is also commonly found in Mississippian marine limestones. In the photograph the corallites are long, cylindrical and thick walled. They are usually interconnected by horizontal tubuli.

Dibunophylum is a spectacular solitary coral. In cross section note the size re-crystallised axial structure i.e. one third as wide as the corallum - this is a distinctive feature of this coral. The major septa almost reach the axial structure whilst minor septa are discontinuous. The dissepiments are small and numerous