Phylogenetic reconstruction of scleraxonian octocorals supports the resurrection of the family Spongiodermidae (Cnidaria, Alcyonacea)

Abstract

The Scleraxonia are a group of octocorals that share similarities of their axis morphology. However, molecular phylogenetic analyses have shown this group to be largely polyphyletic. As a result, there is a significant lack of understanding of what constitutes distinct evolutionary units among members of this group, particularly at the family level. Prompted by the discovery of an unknown spongiodermid scleraxonian octocoral (Anthothelidae) from shallow water off the Pacific coast of lower Baja California, a phylogenetic analysis of the undescribed specimen, together with members of six scleraxonian families and an additional 29 non-scleraxonian octocorallian families was performed. Two mitochondrial loci (mtMutS and COI) and one nuclear locus (28S) supported a monophyletic spongiodermid clade (Homophyton, Callipodium, Diodogorgia, Titanideum and Sclerophyton, gen. nov.) at the family-level. The unknown scleraxonian was supported as a new genus and species within the spongiodermid clade, sister to the western Atlantic genus Titanideum. A morphological examination of the taxa within this clade revealed shared morphological similarities in solenial (boundary) canals, and medullar and cortical sclerites. A revision, with illustrations, of the Spongiodermidae was performed. Similar to previous studies, this study underscores the importance of combined morphological and molecular analyses in order to resolve unstable systematic relationships among octocorals.