Sea Pens – Strange Soft Coral


The Sea Pen – A colourful aquatic Animal

The sea pen, a stunning creature of the oceans, is a soft coral. Its name comes from its appearance, which resembles an old-fashioned quill pen. These pens were primarily used in the past.

Sea pens, which are similar to anemones, are colonies of marine cnidarians from the order Pennatulacea. They are a group of polyps that work together for the survival and well-being of the entire colony.


The trunk of the sea pen is formed when the initial polyp sheds its tentacles. The bulb is the base of the sea pen and anchors it in the sandy or muddy seafloor. Secondary polyps are the sea pen’s “branches”, and each has a specialized function.

The sea pen can grow up to 2m (6.6ft) in some species and are often radiantly coloured. Sea pens are rarely found below 10 meters (33 feet) depth. They prefer deeper waters where turbulence will not uproot them.

Plankton is the primary food source for the Sea Pens. Although they aren’t mobile often, they can move about and re-anchor themselves if needed. They can place themselves in the best possible position for plankton flow, so they can be found right in the path of currents.


They are prey to the sea stars and nudibranchs, which can be challenging to find.
Sea pens can emit bioluminescence when touched. They will force liquid out of their bodies as a defence act by deflating and withdrawing into the peduncle. These beautiful marine creatures can be found in warm and tropical waters around the world.

The order Pennatulacea includes sea pens, which are colonies of marine cnidarians. The order has 14 families and 35 genera, and it is estimated that around 200 of the 450 species exist.


Sea pens have a diverse array of habitats. They can be found in temperate and tropical waters worldwide, at depths up to 6100m. The sea pen is often grouped with gorgonians or sea whips.

The group is known for its resemblance to antique quill pen species. Still, only Subselliflorae sea pen species can live up to this comparison. The more extensive Sessiliflorae suborder lacks feathery structures and grows in radiating or club-like forms. This suborder is often referred to as sea-pansies.

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The Cambrian-aged Burgess Shale (Thaumaptilon) is where the earliest known specimens were identified. Similar specimens from Ala Charnia (the Ediacaran) could reveal the origins of the sea pen. It is not known what these early fossils might be.

Sea pens are octocorals that have many polyps. They look a lot like miniature sea anemones, and each has eight tentacles. Sea pen polyps have specialized functions, unlike other octocorals. One polyp becomes a stiff, straight stalk (the “rachis”) and loses its tentacles to form a bulbous root or peduncle at the base.


Carbonate is used to support the entire colony. It can be found in the form of spicules or a central axial pole. The opposite polyps develop from this central stalk, creating water intake structures (siphonozooids), food structures (autozooids), and reproductive structures.

Sea pens use their roots-like peduncles for stability in sandy or muddy substrates. In some species, such as the tall sea pen Funiculina quadrangularis, the exposed area can reach up to 2m (6.6ft). Sometimes sea pens can be brilliantly coloured. The orange sea pen (Ptilosarcus gurneyi), maybe a well-known one.


Rarely found above 10m (33ft) in depths, sea pens prefer deeper waters where turbulence will not uproot them. Some species can be found at depths up to 2,000m (6,600 feet) for some species.

Sea pens are generally mobile animals but can move & re-anchor their own bodies if necessary. They favourably place themselves in the path and flow of currents to ensure a steady supply of plankton, which is the primary source of their sustenance. They are the prey of nudibranchs and sea stars, which eat sea pen larvae primarily.


Sea pens can be clumped together spatially and collectively, which hinders sea stars’ predation strategies. Some sea pens emit glowing greenish light when touched. This is sometimes called bioluminescence. For defence, they will push water out of the bodies and retreat into their peduncles.

Sea pens reproduce in the same way as other anthozoans by coordinating the sperm and eggs released into the water column. This can happen seasonally or throughout the year. Planulae are the larvae that emerge from fertilized eggs.


They drift for about a week before they settle on the substrate. Mature sea pens provide shelter for young fish and other animals. According to rachis rings, sea pens can live up to 100 years if they are, in fact, annual.

Some sea pens exhibit glide reflection symmetry, unique among non-extinct animals.

Sea Pen Facts

What do sea pens do?

There are many species of octocoral. They are named after the eight stinging tentacles used to catch plankton, tiny floating plants and animals for food. Some sea pens use a bulb filled with water to anchor them to the seafloor. All have robust internal skeletons, & at least some of them can radiate in the dark.


Is the sea pen edible?

Sea Pens can’t be eaten. They are not toxic, but they won’t taste good. They are a beautiful addition to the bio-diversified array of sea creatures on the planet.

Where can you find a sea pen?

Sea pens have a communal distribution found in tropical and warmer waters all over the globe deeper than 6100m. These are both classified with the octocorals and together with sea whips or gorgonians.

Further Reading

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