by Hayley D. The sea pen is a colony of polyps (tiny anemone like organisms) that all work together to survive as an entity. The primary polyp discards it’s eight tentacles and becomes the stalk. There is bulb at the base that anchors the sea pen to the sandy sea floor where it lives. Assorted secondary polyps form limbs that each have different jobs that contribute to the colony. Some polyps feed on drifting plankton using nematocysts, other polyps strictly reproduce, while others’ exert water through canals that help to get air circulating through the colony.