Feathery sea pen Virgularia schultzi
Photo by Glenn Rabie
Purple sea pen completely out of the sand, with Pierre's armina feeding on it.
Photo by Guido Zsilavecz
Sea pens have a central "stem" covered with polyps. Often sea pens are cylindrical - for example see the second image, (from the News 2006 section, the entry for 19 March), which shows a different sea pen, on which a nudibranch feeds. In this image the whole sea pen is visible, including the short peduncle which anchors the sea pen into the soft sand. The feathery sea pen is different, in that it has its polyps arranged like a leaf or a feather. It can twist the body so that the feather is always broadside to the current or surge, maximising the area to catch prey. Sea pens belong to the cniderians, to which anemones and soft corals also belong.
Two Oceans, A guide to the marine life of Southern Africa, GM Branch, CL Griffiths, ML Branch and LE Beckley, 1994.