Sea pen

Sea pens are special kinds of animals that live in the ocean. They belong to a group called marine cnidarians, which also includes jellyfish and corals. Sea pens look like tiny forests stuck to the ocean floor. Their bodies are made of many tiny animals called polyps that live together in a soft, supportive material.

You can find sea pens all around the world, from warm tropical waters to cold, deep oceans. They live everywhere from the shore you can see at low tide to deep waters more than 6,100 meters (20,000 feet) below the surface.

Scientists have found fossils of sea pens that are very old, from a time called the Cambrian period. These fossils were discovered in a place called the Burgess Shale, and they show us that sea pens have been living in the ocean for a very long time. Even older fossils from a time called the Ediacaran might be the first sea pens, but scientists are still learning more about them.

Taxonomy

Sea pens are special animals called marine cnidarians that belong to a group known as the superfamily Pennatuloidea. They live in colonies on the ocean floor and eat by filtering small particles from the water. This group has many different families, including:

• Anthoptilidae Kölliker, 1880
• Balticinidae Balss, 1910
• Chunellidae Kükenthal, 1902
• Echinoptilidae Hubrecht, 1885
• Funiculinidae Gray, 1870
• Gyrophyllidae López-González,Drewery & Williams, 2022
• Kophobelemnidae Gray, 1860
• Pennatulidae Ehrenberg, 1834
• Protoptilidae Kölliker, 1872
• Pseudumbellulidae López-González in López-González & Drewery, 2022
• Renillidae Gray, 1870
• Scleroptilidae Jungersen, 1904
• Stachyptilidae Kölliker, 1880
• Umbellulidae Lindahl, 1874 (1840)
• Veretillidae Herklots, 1858
• Virgulariidae Verrill, 1868

Biology

Sea pens are special kinds of animals called octocorals, living in groups called colonies. Each small part of the colony, called a polyp, looks a bit like a tiny sea anemone and has eight tentacles. In sea pens, one polyp grows into a stiff stalk, while others form structures for feeding and reproduction. The whole group is held together by a hard rod made of calcium carbonate.

Sea pens live stuck to the ocean floor, often in deep water, and can grow up to 2 meters tall. They are usually found in deeper parts of the sea where they are less likely to be moved by waves. Some sea pens can glow in the dark when touched, a process called bioluminescence. They eat by catching tiny animals and plants floating by in the water currents. Other sea creatures sometimes hide among sea pens for safety.

Aquarium trade

Sea pens are sometimes sold for use in aquariums. They can be tricky to care for because they need a deep area of sand or mud at the bottom and special kinds of food to stay healthy.