The slender sea pen (''Virgularia mirabilis'') is a species of

sea pen Sea pens are marine cnidarians belonging to the superfamily Pennatuloidea, which are colony-forming benthic filter feeders within the order Scleralcyonacea. There are 14 families within the order and 35 extant genera, and it is estimated a ...

in the family Virgulariidae, occurring throughout the Mediterranean and Western Europe, with some colonies being found on islands in the Mid-Atlantic.

Description

The slender

stands upright in fine sediments. Their peduncles are buried underneath the sediment, while their raches extend into the water column. Due to their location in fine sediments, they are known to be able to withdraw into the sediment very quickly. They are able to reach up to 60 cm in length. It forms elongated and slender colonies, with

polyps A polyp in zoology is one of two forms found in the phylum Cnidaria, the other being the medusa. Polyps are roughly cylindrical in shape and elongated at the axis of the vase-shaped body. In solitary polyps, the aboral (opposite to oral) en ...

living on attached side branches. The polyps that form on the slender sea pen are able to form groups as large as 16 on each branch, with the central stem being only a few millimeters thick. The slender sea pen's color ranges from white, to beige, to a light yellow. Research shows that the nerve net in the slender sea pen seems to be well-developed.

Habitat and distribution

The slender sea pen is able to live in both shallow, sheltered locations, as well as up to depths of 400 m. The species is located primarily in the waters of Western Europe, but has also been found in the waters of the

Mediterranean The Mediterranean Sea ( ) is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean basin and almost completely enclosed by land: on the east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern ...

and the Mid-Atlantic. In the Mediterranean, research has shown that the slender sea pen is mainly limited to the continental northern shelves. They are known to have been found farther west, having been located as far as the

Azores The Azores ( , , ; , ), officially the Autonomous Region of the Azores (), is one of the two autonomous regions of Portugal (along with Madeira). It is an archipelago composed of nine volcanic islands in the Macaronesia region of the North Atl ...

in the Mid-Atlantic. In Western Europe, the slender sea pen is commonly found along all the coasts of the

British Isles The British Isles are an archipelago in the Atlantic Ocean, North Atlantic Ocean off the north-western coast of continental Europe, consisting of the islands of Great Britain, Ireland, the Isle of Man, the Inner Hebrides, Inner and Outer Hebr ...

. It is one of the most abundant and widespread of all the British sea pen species, as it has a tolerance to a wide variety of

sediment Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...

s, salinities, and temperatures. In surveys completed off the coast of the western coast of

Scotland Scotland is a Countries of the United Kingdom, country that is part of the United Kingdom. It contains nearly one-third of the United Kingdom's land area, consisting of the northern part of the island of Great Britain and more than 790 adjac ...

, the slender sea pen has shown to prefer

salinity Salinity () is the saltiness or amount of salt (chemistry), salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensio ...

from 27 to 35, muddy sediments with low percentage of gravel, and depths from 5 to 200 m.

Ecology

Slender sea pens typically feed on

zooplankton Zooplankton are the heterotrophic component of the planktonic community (the " zoo-" prefix comes from ), having to consume other organisms to thrive. Plankton are aquatic organisms that are unable to swim effectively against currents. Consequent ...

and other organic particles, however they also have been known to feed upon small animals that have been swept into their branches. They possess

nematocysts A cnidocyte (also known as a cnidoblast) is a type of cell containing a large secretory organelle called a ''cnidocyst'', that can deliver a sting to other organisms as a way to capture prey and defend against predators. A cnidocyte explosively ...

, so the species is capable of both passive predation of small animals and suspension feeding of particles. The species is primarily a passive carnivore, but will also suspension feed when particles become trapped in the mucus on the ends of their branches. Slender sea pens are not associated with many other

fauna Fauna (: faunae or faunas) is all of the animal life present in a particular region or time. The corresponding terms for plants and fungi are ''flora'' and '' funga'', respectively. Flora, fauna, funga and other forms of life are collectively ...

. Due to their ability to retract into the sediment, they are not very suitable for

epizoic An epibiont (from the Ancient Greek meaning "living on top of") is an organism that lives on the surface of another living organism, called the basibiont ("living underneath"). The interaction between the two organisms is called epibiosis. An ep ...

organisms to sit on

Reproduction

The sexes are separate, with each colony of polyps being either male or female. Each colony will remain the same sex for their entire life span. The frequency of their reproduction is annually episodic, with reproduction happening between June and October. The larvae have the ability to disperse over a length of 10 km. Little other information is known about the reproductive cycles of slender sea pen, though research inter similar species suggests that up to 200,000 eggs could be produced per female colony.

References

{{wikispecies Virgulariidae