Sea Pens – Strange Soft Coral

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The Sea Pen – A colourful aquatic Animal

A stunning creature of the seas, the sea pen is a soft coral & gets its name because it resembles a plump, old-fashioned quill pen. Quill pens are pens used mostly during history in recent times.

Comparable to the anemone, sea pens are colonial marine cnidarians belonging to the order Pennatulacea. In other words, they’re a colony of polyps working collectively for the survival of the whole.

The initial polyp loses its tentacles & becomes the sea pen’s trunk. With a bulb at its bottom, the bulb anchors the sea pen in the muddy or sandy seafloor. The assorted secondary polyps constitute the sea pen’s “branches” & have specialised functions.

The sea Pen may grow to 2 meters (6.6 ft) in some varieties, like the towering sea pen (Funiculina quadrangularis), & are sometimes radiantly coloured. Seldom observed over depths of 10 meters (33 ft), sea pens favour deeper waters wherever turbulence is not expected to uproot them.

The Sea Pens’ primary source of nourishment & diet is plankton. Though they don’t move around frequently, they’re able to relocate & re-anchor themselves if necessary. They have a tendency to position themselves favorably within the path of currents, securing a gentle flow of plankton. Their primary predators are the unlikely nudibranchs and sea stars, several of which feed solely on the sea pens.

Some sea pens, when touched, emit a luminous greenish light, attributed to as bioluminescence. They’ll also force liquid out of themselves as a defensive act, deflating & withdrawing into their peduncle. Consequently, the next time you’re diving in an area that these unique ocean creatures grow, keep an eye out for these beautiful marine creatures in tropical & warm waters worldwide.

Sea pens are colonial marine cnidarians belonging to the order Pennatulacea. There are 14 families in the order; 35 extant genera, & it’s estimated that of 450 named species, around 200 are confirmed.

Sea pens have a cosmopolitan arrangement, being found in tropical & temperate waters worldwide, to depths of over 6100m. Sea pens are grouped with the octocorals, alongside sea whips or gorgonians.

Although the group is identified for its supposed likeness to antique quill pens, only sea pen species belonging to the suborder Subselliflorae live up to the comparison. Those of the much more extensive suborder Sessiliflorae lack feathery structures and grow in club-like or radiating forms. The latter suborder includes what is regularly referred to as sea pansies.

The earliest accepted specimens are identified from the Cambrian-aged Burgess Shale (Thaumaptilon). Similar specimens from the Ediacaran (ala Charnia) may reveal the origin of sea pens. Precisely what these early fossils are, however, isn’t determined.

As octocorals, sea pens are colonial creatures with many polyps (which look somewhat similar to miniature sea anemones), each with eight tentacles. Unlike other octocorals, though, a sea pen’s polyps are specialised to particular functions: one polyp grows into a rigid, erect stalk (the rachis) & loses its tentacles, forming a bulbous “root” or peduncle at its base.

The opposite polyps grow from this central stalk, forming water intake structures (siphonozooids), feeding structures (autozooids) with nematocysts, & reproductive structures. The whole colony is supported by carbonate in the type of spicules & a central axial pole.

Utilising their root-like peduncles to secure themselves in the sandy or muddy substrate, the exposed portion of sea pens may get up to 2 metres (6.6 ft) in some species, like the towering sea pen (Funiculina quadrangularis). Sea pens are sometimes brilliantly coloured; the orange sea pen (Ptilosarcus gurneyi) may be a well-known example.

Rarely found over 10 metres (33 ft) over depths, sea pens favour deeper waters wherever turbulence is not likely to uproot them. Some species may occupy depths of 2,000 metres (6,600 ft) or more.

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While generally immobile animals, sea pens can relocate & re-anchor themselves if need be. They place themselves favourably in the path of currents, assuring a gentle flow of plankton, the sea pens’ principal source of sustenance. Their chief predators are nudibranchs & sea stars, several of which feed exclusively on sea pens.

The sea pens’ ability to be clumped collectively & spatially hinders the sea stars’ predation techniques. When touched, some sea pens emit a glowing greenish light; this is often mentioned as bioluminescence. They’ll also push water out of their bodies for defence, immediately deflating & retreating into their peduncle.

Like other anthozoans, sea pens reproduce by co-ordinating sperm & eggs released into the water column; this might occur seasonally or during the year. Fertilised eggs become larvae called planulae, which drift freely for around a week before settling on the substrate. Mature sea pens give shelter for other animals, like young fish. Investigation of rachis growth rings shows sea pens may live for 100 years or longer if the rings are indeed annual in nature.

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

Sea Pen Facts

What do sea pens do?

Sea pens are various octocoral, named for the eight stinging tentacles they use to catch plankton (tiny floating plants & animals) to feed themselves. 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 are not generally edible. Although not toxic to humans, they wouldn’t taste very nice. Why would you want to eat one anyway, as they are a beautiful addition to the bio-diversified assortment of colourful sea creatures on the planet?

Where are sea pens found?

Sea pens have a communal distribution, being found in tropical & warmer waters around the world, & can be found at depths of more than 6100m. Sea pens are classified with the octocorals, together with sea whips or gorgonians.

Further Reading

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Sea pens - strange soft coral