Sea pen

The sea pen is a soft coral that earned its name because it looks like an antique fountain pen. Sea Pens are known to live in colonies, and are made up of 14 different families. They can be found in the tropical and moderate climates. As an octocoral (soft coral), the sea pen is made up of polyps. Other members of the octocorals include sea whips and sea feathers.

There are two main suborders for the sea pen. They are the Subselliflorae and the Sessiliflorae. The Subselliflorae order is known to look like the fountain pens. However, the much larger order Sessiliflorae, lack the feathery appearance and are sometimes known as sea pansies. 

Anatomy
The sea pen is named for its feathery appearance. The sea pen has a bilateral symmetry. It is actually just one big polyp. The polyp starts out very large and then loses its tentacles, making the central axis. The base of the main polyp forms a bulb (peduncle) which digs into the ground and anchors itself into the sand. Some species of the sea pen can grow to be 2 meters above ground.

Reproduction
Like most other Anthozoans, sea pens release their sperm into the water. This is commonly a seasonal process but can be done throughout the year. The fertilized eggs turn into larvae and float around in the water for about a week until they are able to plant themselves into the ground. 

Ecology
The sea pen is usually sessile, but is able to relocate if needed. The main reason for them needing to move would be because of lack of plankton; the primary source of food. The predators to sea pens are nudibranchs and sea stars. When touched, the sea pen emits a bright green light practically blinding its predator. They are also able to force water out of themselves and then retreating into the peduncle. Groups of sea pens offer food and shelter to many organisms including the juvenile rockfish. Most sea pens are able to live to over 100 years.