Sea pens may be some of the most unique creatures in an ocean environment. They are marine cnidarians that live in clusters, resembling one individual creature that is very reminiscent of an old-fashioned quill pen. These creatures, known as polyps, work together to benefit the entire organism.
Sea pens come in a variety of colors and sizes. They can grow up to 2 feet (60 cm) in length and are often found in tropical waters, but can be found in cooler waters as well. Their color ranges from dark orange to yellow and white. Some even express qualities of bio-luminescence at night.
Found on the bottom of the ocean floor, their shape makes them very distinguishable. They can be found to a depth of up to 225 feet (68.5 m). They are present both in inshore waters and deeper offshore waters where the current is calmer. However, because they are suspension feeders, they do need some type of current in order to move food into their grasp.
Though sea pens are very easy to overlook and not much is known about them, they may be one of the most abundant type of cnidarians on the planet. In fact, one researcher estimates the mass of tissue in sea pens would equal or surpass that of all other cnidarians combined. Given this abundance, it is somewhat surprising more research has not been done on them.
Sea pens open up in their full splendor at approximately the time they begin feeding. They are suspension feeders, meaning they depend on drifting organic particulates and zooplankton in order to get their energy. Once done feeding the sea pens then retreat and contract. This process usually takes place several times a day.
Sea pens are especially vulnerable to some predators. Sea stars, especially feed heavily on sea pens. Sea pens can also fall prey to a number of diseases, including a parasitic form of green algae. However, if left without predation or disease, sea pens can live as long as 15 years.
Sea pens can also be kept in aquariums and tropical varieties can be very popular. However, they may not be recommended for amateurs as they take a considerable amount of space and expertise in their care. They must be fed a specialty food and need a base of sand of at least 1 foot (30 cm) in order to give them a good anchor.