Phylogenetic position of the reef-builder Madrepora carolina and the genus Thalamophyllia (Anthozoa, Scleractinia): new additions for the family Agariciidae

Abstract

The family Madreporidae Ehrenberg, 1834 (Anthozoa, Scleractinia), includes some of the most important mesophotic and deep-sea habitat-forming species of stony corals. However, molecular data are completely lacking for some of its species, preventing the test of their phylogenetic position. The integration of molecular and morphological data in scleractinian taxonomy has revealed the presence of several para- or polyphyletic lineages, which in most cases are still waiting for a revision. Here, using a genomic approach that couples nuclear ultraconserved and exon loci and complete mitochondrial genome features, we investigate the phylogenetic position of three Madrepora Linnaeus, 1758 species - sequenced for the first time - and the genus Thalamophyllia Duchassaing, 1870. The latter has been historically assigned to the family Caryophylliidae Dana, 1846, but recent molecular studies have found it more closely related to the phylogenetically distant family Agariciidae Gray, 1847. Here, we present congruent nuclear and mitochondrial results placing the species Madrepora carolina (Pourtalès, 1871) and the genus Thalamophyllia inside the family Agariciidae. Specifically, both taxa present the canonical mitochondrial gene order - shared with the family Agariciidae and the majority of stony corals - while lacking the specific gene transpositions characteristic of the families Madreporidae and Caryophylliidae, respectively. The genus Thalamophyllia and the species M. carolina are, therefore, formally moved to the family Agariciidae, and M. carolina is accommodated in a new genus ( Pseudomadrepora Vaga & Quattrini gen. nov.). The results of this study uncover another case of macromorphological skeletal convergence in the order, while untangling the relationship of some deep-water scleractinian taxa.