Bougainvillia muscus is a colonial hydrozoan (family Bougainvilliidae) distributed in temperate and boreal coastal waters of the North Atlantic and Pacific, forming branching, moss-like growths on rocks, shells, and algae in intertidal and shallow subtidal zones. The medusa stage is small, umbrella-shaped, and planktonic, with branching tentacles arranged in clusters at each corner of the bell margin. The species is representative of the diverse colonial hydrozoan fauna of temperate shorelines. Genomic data have been generated for this species and are available in public databases, enabling comparative studies of cnidarian evolution and ecology.