Marine Animal Encyclopedia
Orange Sea Pen Ptilosarcus gurneyi
Unlike the majority of anthozoans, sea pens live in areas of sand and mud. They get their name from their resemblance to an old-fashioned quill pen. The orange sea pen consists of a central stem with branches on either side. The basal part of the stem is bulbous and anchors the colony in the sediment. Single rows of polyps extend their eight tentacles into the water from each leaflike branch, giving the front of the sea pen a downy appearance. The colony faces toward the prevailing current to maximize the flow of plankton over the feeding polyps. When no current is flowing, the colony can retract down into the sediment. Although they tend to stay in one place, colonies can relocate and re-anchor themselves if necessary. Predators of orange sea pens include sea slugs and starfish.