Sea pen

For other uses, see Pen (disambiguation).

Sea pens Temporal range: Cambrian–Recent PreЄ Є O S D C P T J K Pg N

"Pennatulida" from Ernst Haeckel's Kunstformen der Natur, 1904
Scientific classification
Kingdom:	Animalia
Phylum:	Cnidaria
Class:	Anthozoa
Subclass:	Octocorallia
Order:	Pennatulacea Verrill, 1865
Families
Suborder Sessiliflorae Anthoptilidae Chunellidae Echinoptilidae Funiculinidae Kophobelemnidae Protoptilidae Renillidae Scleroptilidae Stachyptilidae Umbellulidae Veretillidae Suborder Subselliflorae Pennatulidae Pteroeididae Virgulariidae

Sea pens are colonial marine cnidarians belonging to the order Pennatulacea. There are 16 families within the order; they are thought to have a cosmopolitan distribution in tropical and temperate waters worldwide. Sea pens are grouped with the octocorals ("soft corals"), together with sea whips or gorgonians.

Although named after their feather-like appearance reminiscent of antique quill pens, 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 (Thaumaptilon). Similar fossils from the Ediacaran (ala Charnia) may represent the dawn of sea pens. Precisely what these early fossils are, however, is not decided.

Biology

Uprooted sea pen with the bulbous peduncle in view

As octocorals, sea pens are colonial animals with multiple polyps (which look somewhat like miniature sea anemones), each with eight tentacles. 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.^[1] 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 2 metres (6.6 ft) in some species, such as the tall sea pen (Funiculina quadrangularis). Sea pens are sometimes brightly coloured; the orange sea pen (Ptilosarcus gurneyi) is a notable example. Rarely found above depths of 10 metres (33 ft), sea pens prefer deeper waters where turbulence is less likely to uproot them. Some species may inhabit depths of 2,000 metres (6,600 ft) or more.

While generally sessile animals, sea pens are able to relocate and re-anchor themselves if need be.^[1] They position themselves favourably in the path of currents, ensuring a steady flow of plankton, the sea pens' chief source of food. Their primary predators are nudibranchs and sea stars, some of which feed exclusively on sea pens. When touched, sea pens emit a bright greenish light; this is known as bioluminescence. They may also force water out of themselves as a defensive act, deflating and retreating into their peduncle.

Like other anthozoans, sea pens reproduce by co-ordinating 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. 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,^[2] which is rare among non-extinct animals (see Glide reflection § Glide reflection in nature and games).

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.

Gallery

Pennatula aculeata
Sea pen at Vancouver Aquarium
Orange Sea Pen (Ptilosarcus gurneyi) at California Academy of Sciences
Sea pen in East Timor

References

1 2 Barnes, Robert D. (1982). Invertebrate Zoology. Philadelphia, PA: Holt-Saunders International. pp. 168–169. ISBN 0-03-056747-5.
↑ Zubi, Teresa (2016-01-02). "Octocorals (Stoloniferans, soft corals, sea fans, gorgonians, sea pens) - Starfish Photos - Achtstrahlige Korallen (Röhrenkorallen, Weichkorallen, Hornkoralllen, Seefedern, Fächerkorallen)". starfish.ch. Retrieved 2016-09-08.

External links

Wikimedia Commons has media related to Pennatulacea.

Wikispecies has information related to: Pennatulacea

Photos of Sea Pens

Corals and coral reefs

Stony corals	Scleractinia Blue coral Brain coral Elkhorn coral Hermatypic coral Chalice coral Pillar coral Staghorn coral Table coral

Soft corals	Alcyonacea Black coral Bamboo coral Organ pipe coral Sea fans Sea pens

Coral reefs	Atoll reef Cay Fringing reef Microatoll Coral reef fish Census of Coral Reefs The Structure and Distribution of Coral Reefs Catlin Seaview Survey

Coral regions	List of reefs Deep-water coral African coral reefs Amazon Reef Andros, Bahamas Belize Barrier Reef Coral Sea Islands Coral Triangle Florida Keys National Marine Sanctuary Great Barrier Reef Maldives Mesoamerican Barrier Reef System New Caledonia Barrier Reef Pulley Ridge Raja Ampat Islands Red Sea Southeast Asian coral reefs

Coral diseases	Coral bleaching Black band disease Skeletal eroding band White band disease White pox disease

Protection	Coral Reef Alliance Coral reef protection Green Fins International Society for Reef Studies Project AWARE Reef Check Reef Ball

Other	Artificial reef Aquaculture of coral Coral dermatitis Precious coral Coral rag Coral reef organizations Coral sand Coralline alga Environmental issues with coral reefs Fire coral Reef resilience Rugosa (extinct) Symbiodinium Tabulata

Taxon identifiers	EoL: 1828 GBIF: 710 ITIS: 52348 NCBI: 6133 WoRMS: 1367

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