Range: Marine waters worldwide Habitat: Sandy or muddy habitats Size: About 0.5 feet-6 feet (15.24cm-1.8m) long Diet: Shrimp, fish larvae, copepods, and plankton Threats: Sea slugs and more Life span: One decade or older

Transcript:

Today on Animal Fact Files we’re talking about sea pens. Originally thought to be a cross between plants and animals thanks to their plant-like appearance, sea pens are definitely animals and are often referred to as a type of soft coral. They get their common name “sea pen” because they superficially look like old-timey quill pens; in fact, the sea pens that look like this are sometimes referred to as feather pens, as well, but they don’t always look this way! Some sea pens can be umbrella-shaped, whip-shaped, and even heart-shaped! The flatter sea pens are sometimes also called sea pansies, so even today they haven’t escaped that plant-like comparison.

The whip shaped sea pens are the longest and can reach more than six feet (1.8 meters) in length, though other species are barely over half a foot (15.24 centimeters) long. There are currently somewhere around 200 valid species of sea pens, but this can change with new information.

Sea pens are a cosmopolitan group, meaning they’re found throughout the world. They may inhabit areas anywhere from polar regions all the way to tropical waters, and they may live in tidal zones or more than three and a half miles (5.6 kilometers) below the ocean’s surface. Generally, sea pens prefer sandy or muddy bottoms, though some species will attach themselves to hard substrates such as rocks. They’re mostly nocturnal animals, though there are some who prefer sunshine and we’ll explain why in just a bit!

Sea pens spend most of the day scrunched up, and sometimes even buried in the sand, by releasing water from their bodies. At night, they take in more water in and fill out to their full size. They are able to give off light especially when touched. When in distress they may shrink back down again, kind of like a hiding Christmas tree worm, or they shine. It’s believed that sea pens give off light to distract and surprise predators. Predators to sea pens include sea slugs, though they aren’t total pushovers.

Because they’re cnidarians, sea pens are able to sting. While the strength of their sting may not be as intense as something like a sea wasp, they’re still able to catch food in the form of tiny shrimp, fish larvae, and copepods along with plankton-sized morsels. Some sea pens form symbiotic relationships, too, such as those who harbor zooxanthellae. These sea pens specifically are diurnal, and the reason for this is so that their symbiotic algae friends are able to catch the rays of the sun. This is similar to the giant clams we’ve talked about previously.

A sea pen’s body structure consists of the main stalk, called the central axis. From this stalk, a polyp will produce clones of itself through budding. These clones creating the branching, feathery-like projections. The budded polyps mainly serve two purposes, circulating water throughout the sea pen’s body, as well as eating and reproducing.

Sea pens reproduce by releasing sperm and eggs into the water column. After fertilization, the eggs will hatch planulae that are free swimming and don’t eat. It make take just a day or two or it make take weeks, but after a time the planulae will settle on the ocean floor and become a polyps. This polyp will grow into that central axis and then the process begins all over again! Sea pens living in colder areas likely develop faster, which is in complete opposition to the swordtail fish we’ve talked about previously. In some areas, sea pens may live to be older than a decade.

For more facts on sea pens, check out the links in the description. Thank you to aether slugster for today’s request. Give a thumbs up if you learned something new today, and thank you for watching Animal Fact Files!