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 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.
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.
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.
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.
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.
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.
Some sea pens, like this specimen from a collection, resemble whips.
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.
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.
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.
A shrimp rests on the polyp leaves of this nocturnal Virgularia sea pen near Maricaban Island, Philippines. This sea pen measures about 4 inches (10.2 centimeters).
While some sea pens live in shallow water, others inhabit the dark, cold depths. They have been found as deep as 20,013 feet (6,100 meters) underwater, where they wait in the dark for the rain of tiny, dead plankton. This Umbellula was take from water 1,020 feet deep (311 meters) off Lubang Island, Philippines.
This species of Umbellula lives in the pitch black water near Antarctica, where it grows to 10 feet (3 meters) long with a big head of polyps that is pushed along in the current.