Systematic position and status of Corallimorpharia in Hexacorallia have been controversial because members of Corallimorpharia have intermediate morphology between Actiniaria and Scleractinia. Inferences concerning monophyly and sister relationships of corallimorpharians using morphological and molecular characters have been inconsistent. The inconsistency may be caused by poor taxon sampling of Corallimorpharia. Doubts about the phylogeny of Corallimorpharia persist.

I conducted phylogenetic analyses using morphological and molecular data to provide a comprehensive investigation of phylogeny of Corallimorpharia. Morphological and molecular data were congruent, and all data sets support monophyly of Corallimorpharia, and sister relationship with Scleractinia. Within Corallimorpharia, two evolutionary lineages, cylindrical body corallimorpharians and discoidal body corallimorpharians, were recovered.

Due to the lack of unique morphological characters defining Corallimorpharia, the scleractinian skeleton, which is the only character to separate Corallimorpharia from Scleractinia, is essential to determine the hierarchical rank of Corallimorpharia in Hexacorallia. One hypothesis is that the scleractinian skeleton is not homologous in all scleractinians, and therefore is not phylogenetically meaningful in defining Scleractinia. The hypothesis is supported by evidence from the fossil record, molecular phylogeny of Scleractinia, and environmental effects on calcification.

Therefore, I propose Corallimorpharia and Scleractinia are suborders of the order Madreporaria, as Schmidt (1974) suggested. In Corallimorpharia, there has been no consensus on the number of valid family and genera. I therefore provide a taxonomic revision at the genus-level based on re-examination of type material. I used five morphological character categories that are phylogenetically meaningful. The type species of each genus is redescribed for those known in less detail and diagnostic keys to genera and families are provided. I conclude that there are three valid families and 11 valid genera in suborder Corallimorpharia.

The revision at the genus level is the first step to revise classification at the species level. There is no consensus in the number of valid species in most corallimorpharians genera. There are 41 nominal species in Corallimorpharia. Taxonomic revision at the species level will provide information about diversity and biogeography of corallimorpharians.