Sea pen

Sea pens are interesting animals that live in the ocean. They belong to a group called cnidarians. They look a bit like tiny forests or old-fashioned ink pens stuck in the sand on the ocean floor. That is why they are called "sea pens." These animals are actually groups of very small creatures called polyps. They all live together in a soft, bendable shape.

You can find sea pens all over the world. They live in warm waters near the shore and also in very deep parts of the ocean, more than 6,100 meters (20,000 feet) below the surface. They stay stuck to the seabed. There, they catch food that floats by.

Scientists have found very old fossils of sea pens. These fossils are from a time called the Cambrian period. They were found in a famous place called the Burgess Shale. Some even older fossils from a time called the Ediacaran might be the earliest sea pens, but scientists are still learning about those ancient fossils.

Taxonomy

Sea pens are marine cnidarians that belong to the superfamily Pennatuloidea. They live on the sea floor and catch food from the water. This group has 16 families and about 235 different species.

The superfamily Pennatulacea includes families such as Anthoptilidae, Balticinidae, Chunellidae, Echinoptilidae, Funiculinidae, Gyrophyllidae, Kophobelemnidae, Pennatulidae, Protoptilidae, Pseudumbellulidae, Renillidae, Scleroptilidae, Stachyptilidae, Umbellulidae, Veretillidae, and Virgulariidae.

Biology

Sea pens are animals made of many tiny parts called polyps. They look like small sea anemones. The polyps work together. Some make a stiff stalk, and others help catch food and reproduce. They stick to the ocean floor with their root-like bases and can grow up to 2 metres tall.

Sea pens live in deep, calm waters, sometimes as deep as 2,000 metres. They are often brightly coloured and can glow in the dark when touched. They eat plankton and are sometimes eaten by nudibranchs or sea stars. Sea pens can live for many years.

Aquarium trade

Sea pens are sometimes sold in aquariums. But they can be hard to keep. They need deep sand or mud at the bottom and special food to stay healthy.