PennatulaceaPen*nat`u*la"ce*a\, n. pl. [NL. See Pennatula.] (Zo["o]l.) A division of alcyonoid corals, including the seapens and related kinds. They are able to move about by means of the hollow muscular peduncle, which also serves to support them upright in the mud. See Pennatula, and Illust. under Alcyonaria.