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Previous research supports the idea that all sea pens anchor to soft sediment using a long, basal, peduncle. The discovery of several pennatulacean sea pen species (rockpens) with an adaptation to bind to rocky substrata alters this understanding. The evolutionary history of octocorals, including these sea pens, has long been poorly understood due to a slow rate of mitochondrial gene evolution and a consequent lack of phylogenetically informative molecular markers to distinguish species. The objective of this project is to analyze three species of rockpens (Calibelemnon francei, Anthoptilum gowlettholmesae, Anthoptilum sp. Alaska) and other octocorals to construct a phylogeny to better understand the evolutionary relationships between these taxa. Using preserved specimens from the California Academy of Sciences' Department of Invertebrate Zoology, the genes of ten octocoral species were analyzed. This project sequenced three protein-coding mitochondrial genes, ND2, ND6, and msh1, and phylogenetic tree construction and analysis were done using Geneious and R Studio. Additionally, SEM photographs of the sclerites were used to morphologically characterize the taxa. We hypothesize that all rockpens actually belong to the genus Anthoptilum and form a monophyletic clade with other species of the genus that do not inhabit rocky substrata. Future research will require investigating how other non-rock inhabiting species in the genus Anthoptilum are phylogenetically related to the rockpens.