Meeting Abstract
Octocorals are a diverse group of, for the most part, non-reef building corals accounting for almost 65% of global coral diversity. Sea pens are a highly specialized group of octocorals inhabiting both shallow and deep water ecosystems. The evolutionary origin of sea pens and their interspecies relationships have historically been a point of contention among zoologists, with only recent molecular methods being able to elucidate systematic relationships. Here we present a molecular analysis of six sea pen genera alongside representatives from the Calcaxonia, Scleraxonia, Holaxonia, and soft coral groups using the NADH 2, NADH 6, and msh1 mitochondrial genes. All specimens were collected in the central Philippines, which is an extremely high marine biodiversity area. We found the sea pens to be monophyletic with the calcaxonian family Ellisellidae, confirming previous studies. We also found the sea pen genera Veretillum and Cavernulina to be highly derived within the sea pen clade, refuting past hypotheses that Veretillid sea pens are among the least derived. Instead, our analysis shows the genus Virgularia with well differentiated polyp leaves to be the most basal. Because the sea pen clade is monophyletic with the Ellisellids, which inhabit shallow to mid-deep water, further studies are aimed at investigating whether the sea pens originated and diversified in the shallows and subsequently adapted to deep water ecosystems. A comprehensive sampling of both sea pens and calcaxonians from all depths is the next step in investigating the origin and radiation of sea pens, giving us valuable information about adaptations to different bathymetric environments in an age with rapidly rising sea levels.
