Sea Pens are found anchored in soft or sandy substrates. They live in a range from below the low-tide line to water more than 30 meters (100 feet) deep. Sea Pens grow to be about 46 centimeters high and 102 millimeters wide. They consist of 20 pairs of flat, wide side branches with rows of polyps along both edges. The Sea Pen was named after the quill pen which it looks like. The Sea Pen is not actually one animal, but rather consists of many separate animals called polyps living in a colony. The polyps look like miniature sea anemones each with eight tentacles. Sea Pens reproduce by spawning. Typical egg size is 500-600 micrometers. The peak breeding season occurs from March until April. Fertilized ova develop into planula, which are non-feeding & free-swimming and usually settle quickly. Once settled, the planula larva metamorphose into a polyp and their base becomes a stem. The secondary polyps grow laterally from this structure. The juveniles grow rapidly; they can survive unfed for weeks.
Sea pens are colonial and although considered sessile, they can move up to 40 centimeters by slow creeping on their vertical axes while still attached to their substrates. One behavioral characteristic found in all sea pens is that they have the ability to bury themselves. If disturbed, they contract and withdraw into the muddy bottom by releasing large amounts of water from their canal system. A Sea Pen is a planktonic feeder. The autozooid branch of the polyp filters minute organisms into the main axis of the Sea Pen. These organisms are digested by fluid secreted from special filaments. The particles are phagocytized and passed to mesogloeal cells, in which the digestion process is completed. Sea Pens have inhabited the earth’s surface for hundreds of millions of years. Currently, their numbers are not declining or threatened. Because Sea Pens are vulnerable to dredges used for oyster harvesting, the only threat to their survival arises from humans. Sea Pens are found throughout the world, from tropical to Antarctic waters.