Strange Coral: A Gallery of Sea Pens

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Dinner Time

Veretillum Sea Pen Coral Feeding — (Image credit: Gary C. Williams, California Academy of Sciences)

A nocturnal Veretillum sea pen gathers dinner with its flower-like polyps unfurled as it feeds using the eight tentacles surrounding each polyp's mouth.

A Sea Pen Out of Water

Pteroeides Sea Pen Coral — (Image credit: Gary C. Williams, California Academy of Sciences)

A sea pen that belongs to the genus Pteroeides after it was collected from 60 feet (18.3 meters) of water near Maricaban Island, Philippines. The yellow and orange section of its stalk is called a peduncle. It anchors the sea pen to the ocean floor. The dark, leaf-like structures contain the polyps, each with a mouth surrounded by tentacles. An individual sea pen can also be considered a colony of polyps.

On the Sea Floor

Although it looks much different, this is the same animal shown in the previous picture, before being plucked from its watery home near Maricaban Island, Philippines and taken to the surface.

Night Life for Sea Pens

Pteroeides Sea Pen Coral at Night — (Image credit: Gary C. Williams, California Academy of Sciences)

Another species of Pteroeides, this time at night, near Calumpan Peninsula, Luzon, Philippines. Some sea pens prefer the night life, hiding under the sand or sediment during the day and emerging, with branches of mouths and tentacles searching for tiny morsels of plankton for dinner.

Boney Branches

Pteroeides Sea Pen Coral Skeleton — (Image credit: Gary C. Williams, California Academy of Sciences)

Sea pens, a type of coral, have hard, internal skeletons, visible in this Pteroeides as thin white ribs in its branches. In addition to long skeletal elements, sea pens also have spicules, tiny calcium carbonate particles that give the animals shape and flexibility.

Sheltering Sea Pen

Pteroeides Sea Pen Coral Shrimp — (Image credit: Gary C. Williams, California Academy of Sciences)

A shrimp rests on the lower part of the yellow trunk, or rachis, of this Pteroeides in the Philippines. The photo shows a roughly 6-inch (15.2-centimeter) section of the rachis. Polyp leaves, holding the polyps, branch of the rachis.

Many Forms

Scytalium Sea Pen Coral — (Image credit: Gary C. Williams, California Academy of Sciences)

This sea pen, a species of Scytalium, in the Philippines, is active during the day. Not only can sea pens resemble their namesake, they can look like whips, worms and feathers.

Sea Whip

Some sea pens, like this specimen from a collection, resemble whips.

Many Hungry Mouths

Veretillum Sea Pen Coral — (Image credit: Gary C. Williams, California Academy of Sciences)

The petal-like tentacles surrounding each polyp's mouth on this colorful Veretillum sea pen are clearly visible. Sea pens belong to a particular type of corals, the octocorals, because each mouth is surrounded by eight tentacles.

World Travelers and Homebodies

Virgularia Sea Pen Coral — (Image credit: Gary C. Williams, California Academy of Sciences)

A nocturnal Virgularia sea pen near Maricaban Island, Philippines. Some sea pen larvae settle close to their parents, and others drift on ocean currents, as plankton, until they find the perfect substrate — sand, mud, rubble and in a few cases rock — to which to anchor themselves.

Sea Pen Anatomy

Virgularia Sea Pen Coral Anatomy — (Image credit: Gary C. Williams, California Academy of Sciences)

A colorful species of the nocturnal sea pen Virgularia near Maricaban Island, Philippines. The branches that hold the polyps are called polyp leaves and the stem that supports them is called the rachis. This sea pen's peduncle is buried in the sediment.

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Wynne was a reporter at The Stamford Advocate. She has interned at Discover magazine and has freelanced for The New York Times and Scientific American's web site. She has a masters in journalism from Columbia University and a bachelor's degree in biology from the University of Utah.