Sea pen

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Sea pen
Temporal range: Cambrian–Recent
"Pennatulida" from Ernst Haeckel's Kunstformen der Natur, 1904
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Cnidaria
Class: Octocorallia
Order: Pennatulacea
Verrill, 1865
Family

Pennatulidae

Sea pens are

gorgonians
).

Although the group is named for its supposed resemblance to 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 may show the dawn of sea pens.[3] Precisely what these early fossils are, however, is not decided.[4]

Taxonomy

The order Pennatulacea consists of the following families:[5]

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 pen. [clarification needed] 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.[7]

Uprooted sea pen with the bulbous peduncle in view
Pierre's armina feeding on purple sea pen
Sea pen at Vancouver Aquarium

As

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 (

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.

sea stars, some of which feed exclusively on sea pens. The sea pens' ability to be clumped together and spatially unpredictable hinders sea stars' predation abilities.[9] 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. 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,[10] rare among extant 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

  1. PMID 30471843
    .
  2. ^
    PMID 21829500
    .
  3. ^ Williams, Gary C. "Aspects of the Evolutionary Biology of Pennatulacean Octocorals". Department of Invertebrate Zoology and Geology. California Academy of Sciences. Retrieved 2023-01-27.
  4. S2CID 83486435
    .
  5. ^ "Pennatulacea". World Register of Marine Species. Retrieved 2018-04-03.
  6. S2CID 248243502
    .
  7. doi:10.1016/j.csr.2015.06.007
    .
  8. ^
    ISBN 0-03-056747-5
    .
  9. JSTOR 1942312
    .
  10. ^ 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.
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