One of the most graceful creatures on the sea floor, the Sea Pen resembles an old-fashioned feather pen emerging from the mud. Its colors range from pale to rich orange. Most Sea Pens live in deep water but on low tide days you may see them just beyond the water's edge. In aquariums, this beautiful marine animal always attracts attention.

Each Sea Pen is a colony of small animals, called polyps, working together for survival. Every polyp has eight tentacles and a job. The division of labor among the polyps is pretty cool. Some feed by using stinging cells to catch plankton; some reproduce; some force water in and out of canals to ventilate the colony. Larger Sea Pens, up to 18 inches long, have 40,000 or more polyps working together in this colony that looks to us like a single creature.

After hatching, a young Sea Pen larva swims around looking for a good muddy spot to settle. It becomes the "founder polyp". This polyp multiplies to form the Sea Pen's stalk. The lower half buries itself in mud; the upper half grows feathery branches. The feather shape helps the Sea Pen capture food efficiently while minimizing the drag caused by the turbulent water in which these animals live.

Sea stars and sea slugs, or nudibranchs (pronounced "noo-dĭ-branks"), prey on Sea Pens. When a predator disturbs one, the Sea Pen forces water out of the colony, allowing itself to shrink and retreat into its muddy foot.

Once plentiful in some areas around Puget Sound, Sea Pen populations have declined, affecting the food chain and maybe indicating an ecosystem in trouble.