sea pen

any of several colonial coelenterates of the genus Pennatula and related genera, having the shape of a fleshy feather.
[1755-65]

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      any of the 300 species of the order Pennatulacea, colonial invertebrate marine animals of the class Anthozoa (phylum Cnidaria). The name sea pen derives from their resemblance to quill pens. They occur in shallow and deep waters from polar seas to the tropics.

      The central stalk of the animal consists of a lower part, the peduncle, which anchors the colony in mud or sand, and an upper part, the rachis, which bears polyps (hollow stalks with a mouth and tentacles at the free end) or branches bearing several polyps. The central stalk is known as the primary, or axial, polyp. Those branching from it are the secondary polyps. Colonies of some genera—e.g., Chunella—bear few polyps. Others bear as many as 35,000. The mouth and tentacles of the primary polyp are degenerate, consisting of little more than a fleshy stem strengthened by a central horny rod.

      Many pennatulaceans, however, do not resemble pens. The sea pansy, Renilla, for example, found along the Pacific and Atlantic coasts of North America, is a flattened kidney-shaped plate consisting of two fused halves. All the polyps are on the upper side. The slender rodlike members of the genera Anthoptilum, Funiculina, Balticina, Stylatula, and Virgularia may grow to a length of 2 metres (about 6 1/2 feet). Shorter forms, growing to no more than 20 centimetres (8 inches), have a few relatively large leaves extending from the central stalk (e.g., Leioptilus). Most sea pens are yellow, orange, red, or brown.

      Sea pens can deflate or expand by expelling or taking in water through the interconnecting hollow canals of the polyps. They feed on small organisms captured by the tentacles at the end of each polyp. Most sea pens luminesce (bioluminescence), or glow, when they are touched or otherwise stimulated.

      The secondary polyps are of two types: siphonozooid and autozooid. Siphonozooids draw a current of water through the colony canal system. Autozooids feed and produce eggs and sperm. These gametes are expelled through the mouth into the open water, where fertilization takes place. The ciliated planula, or free-swimming larva, settles to the bottom and metamorphoses to form the axial polyp of a new colony.

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Universalium. 2010.

Look at other dictionaries:

  • Sea pen — Pen Pen, n. [OE. penne, OF. penne, pene, F. penne, fr. L. penna.] 1. A feather. [Obs.] Spenser. [1913 Webster] 2. A wing. [Obs.] Milton. [1913 Webster] 3. An instrument used for writing with ink, formerly made of a reed, or of the quill of a… …   The Collaborative International Dictionary of English

  • sea-pen — Pen Pen, n. [OE. penne, OF. penne, pene, F. penne, fr. L. penna.] 1. A feather. [Obs.] Spenser. [1913 Webster] 2. A wing. [Obs.] Milton. [1913 Webster] 3. An instrument used for writing with ink, formerly made of a reed, or of the quill of a… …   The Collaborative International Dictionary of English

  • Sea-pen — n. (Zo[ o]l.) A pennatula. [1913 Webster] …   The Collaborative International Dictionary of English

  • sea pen — sea′ pen n. ivt any soft coral of the order Pennataluceae, forming feather shaped colonies • Etymology: 1755–65 …   From formal English to slang

  • sea pen — n. any of an order (Pennatulacea) of mud dwelling anthozoans that form feather shaped colonies …   English World dictionary

  • Sea pen — For other uses, see Pen (disambiguation). Sea pens Temporal range: Cambrian–Recent …   Wikipedia

  • sea pen — noun fleshy featherlike warm water colonies • Hypernyms: ↑anthozoan, ↑actinozoan • Member Holonyms: ↑Pennatula, ↑genus Pennatula * * * noun 1. : any of numerous alcyonarians belonging to …   Useful english dictionary

  • sea pen — /ˈsi pɛn/ (say see pen) noun a coelenterate consisting of a central fleshy axis bearing fleshy lateral leaves provided with small polyps, as of the genus Pennatula and related forms …   Australian English dictionary

  • sea pen — noun Date: 1763 any of numerous anthozoans (order Pennatulacea) growing in colonies with a feathery form …   New Collegiate Dictionary

  • sea pen — n. (Zoology) invertebrate marine animal …   English contemporary dictionary


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