Sea pen

Sea pens are fascinating marine animals that belong to a group called cnidarians. They look a bit like tiny forests or old-fashioned ink pens stuck in the sand at the bottom of the ocean, which is why they are called "sea pens." These creatures are actually colonies of tiny animals called polyps that live together in a soft, flexible structure.

You can find sea pens all around the world, from warm tropical waters near the shore to very deep ocean parts that are more than 6,100 meters (20,000 feet) below the surface. They like to stay anchored to the seabed where they can catch food floating by.

Scientists have discovered fossils of sea pens that are very old, from a time called the Cambrian period, found in a famous rock formation known as the Burgess Shale. Some even older fossils from a time called the Ediacaran may be the earliest sea pens, but scientists are still figuring out exactly what those ancient fossils were.

Taxonomy

Sea pens are marine cnidarians that belong to the superfamily Pennatuloidea. They form colonies and live on the sea floor, filtering food from the water. This group includes 16 families and around 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 colonial animals made up of many tiny parts called polyps, which look like small sea anemones. These polyps work together, with some forming a stiff stalk and others helping to catch food and reproduce. They use their root-like bases to stick to the ocean floor and can grow up to 2 metres tall.

Sea pens are usually found in deeper, calmer waters, sometimes as deep as 2,000 metres. They are often brightly coloured and can even glow in the dark when touched. These animals eat plankton and are sometimes eaten by nudibranchs or sea stars. Sea pens can live for many years, possibly over 100 years.

Aquarium trade

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