A molecular and morphological exploration of the generic boundaries in the family Melithaeidae (Coelenterata: Octocorallia) and its taxonomic consequences.

The validity of the currently recognized melithaeid genera (Acabaria, Clathraria, Melithaea, Mopsella, Wrightella) with the exception of the recently added genus Asperaxis, has puzzled scientists for almost a century. Diagnostic morphological characters are often missing or are obscured by the variation in sclerite forms. Consequently, species are difficult to assign to genera. In this study the current genera and their taxonomic positions are reviewed and reassessed based on material collected from the Indo-Pacific, Red Sea and Indian Ocean as far south as South Africa. Molecular data were obtained for four different loci, both mitochondrial (COI, mtMutS, ND6) and nuclear (28S rDNA). Combining the molecular and morphological data revealed that all former genera, except for the monotypic genus Asperaxis and the genus Wrightella are paraphyletic. Molecular data for the two subfamilies (Asperaxinae and Melithaeinae) within the Melithaeidae, in comparison with the outgroup, indicated that the family is also paraphyletic. Furthermore we observed that species did not cluster according to their present morphological classification but instead clustered according to a biogeographical pattern. Species from the Red Sea, Indian Ocean and Central Pacific, respectively, grouped into well supported clades. Consequently, we did not find morphological- or phylogenetic support to maintain the generic names Acabaria, Clathraria, Mopsella and Wrightella. Therefore these names are synonymised with the oldest available generic name, Melithaea. As a result, five secondary homonyms originated; these junior homonyms are herein renamed, viz. Melithaea hendersoni nom. nov, Melithaea mcqueeni nom. nov., Melithaea shanni nom. nov., Melithaea thorpeae nom. nov., and Melithaea wrighti nom. nov. Additionally, neotypes are selected for Melithaea ochracea to stabilize the genus Melithaea, and for Acabaria rubra.