Sea pens are

colonial Colonial or The Colonial may refer to: * Colonial, of, relating to, or characteristic of a colony or colony (biology) Architecture * American colonial architecture * French Colonial * Spanish Colonial architecture Automobiles * Colonial (1920 au ...

marine

cnidaria Cnidaria () is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in freshwater and marine environments, predominantly the latter. Their distinguishing feature is cnidocytes, specialized cells that ...

ns belonging to the order Pennatulacea. There are 14 families within the order; 35 extant genera, and it is estimated that of 450 described

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

, around 200 are valid. Sea pens have a cosmopolitan distribution, being found in tropical and temperate waters worldwide, as well as from the intertidal to depths of more than 6100 m. Sea pens are grouped with the octocorals, together with sea whips ('' gorgonians''). Although the group is named for its supposed resemblance to antique

quill pen A quill is a writing tool made from a moulted flight feather (preferably a primary wing-feather) of a large bird. Quills were used for writing with ink before the invention of the dip pen, the metal- nibbed pen, the fountain pen, and, eventuall ...

s, only sea pen species belonging to the suborder Subselliflorae live up to the comparison. Those belonging to the much larger suborder Sessiliflorae lack feathery structures and grow in club-like or radiating forms. The latter suborder includes what are commonly known as sea pansies. The earliest accepted fossils are known from the Cambrian-aged

Burgess Shale The Burgess Shale is a fossil-bearing deposit exposed in the Canadian Rockies of British Columbia, Canada. It is famous for the exceptional preservation of the soft parts of its fossils. At old (middle Cambrian), it is one of the earliest fo ...

('' Thaumaptilon''). Similar fossils from the Ediacaran (ala '' Charnia'') may show the dawn of sea pens. Precisely what these early fossils are, however, is not decided.

Taxonomy

The order Pennatulacea consists of the following families: **

Chunellidae Chunellidae is a family of sea pens, a member of the subclass Octocorallia in the phylum Cnidaria. Genera The World Register of Marine Species list the following genera: *'' Amphiacme'' Kükenthal, 1903 *''Chunella ''Chunella'' is a monotyp ...

** Echinoptilidae ** Renillidae ** Scleroptilidae ** Stachyptilidae * Suborder Sessiliflorae ** Anthoptilidae ** Funiculinidae ** Kophobelemnidae ** Protoptilidae ** Pseudumbellulidae ** Umbellulidae ** Veretillidae * Suborder Subsessiliflorae ** Halipteridae ** Pennatulidae ** Virgulariidae Image:Actinoptilum molle at Windmill BeachPA111765.JPG, '' Actinoptilum molle'' ( Echinoptilidae) Image:Sea Pansy - Flickr - Andrea Westmoreland (1).jpg, ''

Renilla ''Renilla'' is a genus of sea pen. It is the only genus within the monotypic family Renillidae. Species The following species are recognized: * '' Renilla amethystina'' Verrill, 1864 * '' Renilla koellikeri'' Pfeffer, 1886 * '' Renilla mueller ...

sp.'' ( Renillidae) Image:Pennatula phosphorea.jpg, '' Pennatula phosphorea'' ( Pennatulidae) Image:Veretillum sp. (Sea pen) at night.jpg, '' Veretillum sp.'' ( Veretillidae) Image:Virgularia sp. (Purple sea pen).jpg, '' Virgularia sp.'' ( Virgulariidae)

Biology

Due to the geographic distribution, a result of inflating themselves with seawater which causes them to get carried by the currents, there is genetic variation within the different species of Sea Pens. There are many populations of Sea Pens found in mainly Indian waters. It is their Polyps that are affected genetically, as they have dispersed within the different waters and islands, and how they use their Polyps (tentacles) to protect themselves and other species. Pierre's armina feeding on purple sea pen DSC09784

Pierre's armina feeding on purple sea pen DSC09784

As octocorals, sea pens are colonial animals with multiple polyps (which look somewhat like miniature sea anemones), each with eight

tentacle In zoology, a tentacle is a flexible, mobile, and elongated organ present in some species of animals, most of them invertebrates. In animal anatomy, tentacles usually occur in one or more pairs. Anatomically, the tentacles of animals work ma ...

s. Unlike other octocorals, however, a sea pen's polyps are specialized to specific functions: a single polyp develops into a rigid, erect stalk (the ''rachis'') and loses its tentacles, forming a bulbous "root" or '' peduncle'' at its base. The other polyps branch out from this central stalk, forming water intake structures (''siphonozooids''), feeding structures (''autozooids'') with nematocysts, and reproductive structures. The entire colony is fortified by calcium carbonate in the form of ''spicules'' and a central ''axial rod''. Using their root-like peduncles to anchor themselves in sandy or muddy substrate, the exposed portion of sea pens may rise up to in some species, such as the tall sea pen (''

Funiculina quadrangularis ''Funiculina quadrangularis,'' commonly known as tall sea pen, is an uncommon cold water coral within the Family Funiculinidae. It is named tall sea pen because it looks like a quill sticking in the bottom of the sea. It forms habitat for severa ...

''). Sea pens are sometimes brightly coloured; the orange sea pen (''Ptilosarcus gurneyi'') is a notable example. Rarely found above depths of , sea pens prefer deeper waters where turbulence is less likely to uproot them. Some species may inhabit depths of or more. While generally sessile animals, sea pens are able to relocate and re-anchor themselves if need be. They position themselves favourably in the path of currents, ensuring a steady flow of

plankton Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a crucia ...

, the sea pens' chief source of food. Their primary predators are

nudibranch Nudibranchs () are a group of soft-bodied marine gastropod molluscs which shed their shells after their larval stage. They are noted for their often extraordinary colours and striking forms, and they have been given colourful nicknames to match, ...

s and

sea star Starfish or sea stars are star-shaped echinoderms belonging to the class Asteroidea (). Common usage frequently finds these names being also applied to ophiuroids, which are correctly referred to as brittle stars or basket stars. Starfish a ...

s, some of which feed exclusively on sea pens. The sea pens' ability to be clumped together and spatially unpredictable hinders sea stars' predation abilities. When touched, some sea pens emit a bright greenish light; this is known as bioluminescence. They may also force water out of their bodies for defence, rapidly deflating and retreating into their peduncle. Like other anthozoans, sea pens reproduce by coordinating a release of sperm and eggs into the water column; this may occur seasonally or throughout the year. Fertilized eggs develop into larvae called ''planulae'' which drift freely for about a week before settling on the substrate. Mature sea pens provide shelter for other animals, such as juvenile

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of ...

. Analysis of rachis growth rings indicates sea pens may live for 100 years or more, if the rings are indeed annual in nature. Some sea pens exhibit glide reflection symmetry, rare among non-extinct animals.

Aquarium trade

Sea pens are sometimes sold in the aquarium trade. However, they are generally hard to care for because they need a very deep substrate and have special food requirements.

References

External links

* {{Taxonbar, from=Q1122081 Octocorallia Bioluminescent cnidarians Extant Cambrian first appearances