A coral is placed in a genus and species by examining the fine structure of the skeleton. The general outline of the corallum usually is sufficient to place the coral specimen in the correct genus. However, to obtain the species a closer examination is needed. Below are two perspectives of a common Atlantic coral. The least magnified view can be used to compare the coral with pictures of corals in nature books and obtain a genus, in this case Isophyllastrea .
Further magnification reveals the intricate substructure of the coral cup.
The serrated septa confirm that the species is rigida . The common Atlantic coral, Isophyllastrea rigida , is shown with about a dozen coral cups of various shapes. A look into the coral cup reveals serrated septa. The cup or calice measures approximately 15mm in diameter. The video sequences were filmed in the tropical South Pacific.