MCFADDEN, C.S.*; SANCHEZ, J.A.; FRANCE, S.C.; Harvey Mudd College; Smithsonian Institution; College of Charleston: The evolution of colony morphology in Octocorallia: a phylogenetic approach.

The anthozoan subclass Octocorallia includes the orders Pennatulacea (sea pens) and Alcyonacea (soft corals and sea fans). All but one of the approximately 2000 species in this group are colonial, and most form highly integrated colonies characterized by complex branching patterns and varying degrees of colony polymorphism. A family-level phylogenetic analysis of the subclass suggests that the traditional taxonomic divisions based on growth morphology and skeletal characteristics do not reflect evolutionary relationships within the group. Complex branched morphologies and colony polymorphism appear to have evolved independently in several different clades. A detailed phylogenetic analysis of the soft coral genus Alcyonium suggests that octocoral reproductive traits have also evolved rapidly and reversibly in separate lineages. The apparent evolutionary lability of colony morphology, branching patterns, polymorphism and reproductive mode suggest that octocorals may be useful model systems for understanding the developmental and genetic mechanisms underlying these traits.